5. Чем можно улучшить нашу способность контролировать и использовать?

(Our ability to control and exploit can be improved by an ability to explain and understand, combining both proximal and ultimate explanations.)

Student B:

1. Что прежде всего необходимо сделать, чтобы понять?

(In order to understand , it is necessary first to describe. We must have a description of whatever it is that we wish to understand)

2. Возможно ли предсказать что-либо без понимания и объяснения?

(Some predictions and control can be carried out without explanation or understanding.)

3. Как можно объяснить что-либо в биологии?

(There are two different classes of explanation in biology: proximal and ultimate explanations.)

4. Какие проблемы современной экологии Вы знаете?

(How does it come about that coexisting species are often similar but rarely the same?

What causes predators to adopt particular patterns of foraging behavior?

How have organisms come to possess particular combinations of size, development rate, reproductive output and so on?)

Ex.6. Change your roles and ask and answer the questions again.

Reading C

Ex.1. Render the following article in Russian:

Darwin's (1 859) theory of evolution by natural selection is an ecological theory and rests on a series of propositions.

1The individuals that make up a population of a species are not identical: they vary, although sometimes only slightly, in size, rate of development, response to temperature, and so on.

2Some, at least, of this variation is heritable. In other words, the characteristics of an individual are determined to some extent by its genetic make-up. Individuals receive their genes from their ancestors and therefore tend to share their characteristics.

3All populations have the potential to populate the whole earth, and they would do

so if each individual survived and each individual produced its maximum number of descendants. But, they do not: many individuals die prior to reproduction, and most

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(if not all) reproduce at a less than maximal rate and some of these differences are heritable.

4Different ancestors leave different numbers of descendants. This means much more than saying that different individuals produce different numbers of offspring. It includes also the chances of survival of individuals to reproductive age, the survival and reproduction of their offspring, the survival and reproduction of their offspring in turn, and so on.

5Finally, the number of descendants that an individual leaves depends, not entirely but crucially, on the interaction between the characteristics (or properties) of

the individual and its environment.

Unit 2

Grammar:

1. Participle I, Participle II

Ex.1. Translate the following word combinations paying attention to Participle I and Participle II:

The temperatures experienced at; water distributed at the surface; radiation received in the tropics; variations defined by; energy obtained; extremely localized environments; changing inclination to the sun; opposing ways; a visiting ecologist; undecomposed bodies littering the habitat; to be self-decomposing; tantalizing question; coexisting species; species, having ancestors; supporting tissues; a striking example; low-growing woody plants; species, living mainly on the ground; species falling into the various categories.

2. Perfect Tenses

Ex.2. Read the sentences paying attention to the translation of Perfect Tenses:

1.The history of climatic change of the planet has interacted with its geological history.

2.The mainstream of the earth’s biological activity has depended on solar energy.

3.Laboratory methods have played a crucial role in the development of ecology.

4.Mathematical models have provided important insights into many scientific questions.

5.As we have seen, the key practical question – how common is chaos? – remains largely unanswered.

6.The result in this way might have been expected.

7.The general message is similar to the results that we have already seen.

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8.The population has spread from a single initial patch

9.You might have already seen from several examples, that all environments fluctuate and all populations suffer some random variations.

10.Our previous classifications of habitats and a number of others, have contrasted the average conditions in one habitat with the average conditions in another.

Word Study

Ex.1. Read the words. Give their Russian equivalents:

Atmosphere, solar radiation, distance, planet, character, temperature, phase, gaseous, tropics, evaporation, gas, advective energy, form, geological, formation, mineral, composition, equator, poles, topology, nature, inorganic transformation, methane, sulphur, ammonia, archaebacteria [a:KibæK’tiəriə], photosynthesis, homogeneous, progeny, efficiency.

Ex.2. Translate the following words and word combinations:

Distributed at random; a correspondence between; the order of things; the match between; to move atmosphere; exposed to radiation; vary from place to place; under the influence of; unequally distributed; to drain under gravity; to contribute to the character of the earth’s surface; to decompose at different rates; inclination to the sun.

Ex.3. Words to be remembered:

Relationship, distribute(v), surface of the planet, solid liquid, gaseous phase, provide(v), convert(v), evaporation, weather (geolog.), determine(v), transition in the state, precipitation, at the bottom, variation in the environment, the main stream of biological activity, obtain(v), oxidation, source of power, depend on(v), occur(v), require(v), abundant, scarce.

Reading A: THE NATURE OF ENVIRONMENTS

Ex.1. Read the text. Pay attention to the parameters which determine differences in environments:

Ecology deals with organisms, their environments and the relationship between them. Different kinds of organism are not distributed at random amongst different kinds of environment: there is a correspondence between the two. This correspondence is part of our sense of the order of things. But', what exactly is the nature of the match between organisms and their environment? It is quite impossible to think of an organism without an environment, but it is easily possible to think of environments without organisms. The climate is one component of this environment

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and is determined by the radiation that drives the variations in its temperature and moves its atmosphere, for example its winds. The earth is exposed to solar radiation that varies across its surface. Therefore, the surface of our planet, like that of any other, has a range of environments that vary from place to place. A very special character of our planet is that the temperatures experienced at its surface are in the range in which water can change between solid, liquid and gaseous phases. Moreover, in its gaseous and liquid phases, water is continually moving under the influence of the radiation, which is unequally distributed at the earth's surface. The least radiation is received near the poles and most of the water there is solid ice. The most radiation is received in the tropics where much of it provides the latent heat of evaporation that converts liquid water into gas. Radiation also provides the advective energy that moves clouds of water in gaseous form about the atmosphere and redistributes it on the surface in liquid (rain) or solid form (snow). The surface of theearth is uneven and liquid water drains under gravity from the highlands to the hollows - hence, the environment is partly exposed 'terrestrial, surface and partly 'aquatic' (the oceans, lakes, rivers and puddles).

The planet earth has a history of climatic change that has interacted with its geological history. Various geological formations contribute to the character of the earth's surface. They have different mineral compositions, and they weather and decompose at different rates. The rock formations extend to different heights and, because temperature falls with altitude, the transitions in the state of water may occur with height (i.e. up a mountain), as well as from the equator towards the poles. Water at the top of a mountain may be predominantly solid, yet at the bottom evaporation (loss of water as gas) may exceed precipitation. Near the poles, in parts of the tropics and at both the top and bottom of mountains in the tropics, liquid water may therefore be absent from the environment for most of the time. The variations in the environment of the planet earth are mainly defined by variations in the radiation received in its different parts, and by the topology and nature of its geological formations.

It is conceivable that all the biological activities on a planet such as earth could be powered by energy obtained by inorganic transformations - such as the oxidation of methane, sulphur compounds or ammonia. There are archaebacteria (Archaea) that can indeed do just this, although most of them live in extremely localized and peculiar environments, such as those that are extremely hot or extremely acid. However, the mainstream of biological activity on our planet has depended on solar energy fixed by photosynthesis as its source of power. The result has been that, overwhelmingly, the biological activities on the planet are limited by the efficiency of the photosynthetic process, and depend on incident radiation. But, the intensity of radiation also determines the physical state of water and can therefore act in opposing ways: the distribution of solar radiation determines where and when photosynthesis might occur. Where radiation is abundant (e.g. in the tropics) liquid water may be scarce because it is volatilized, and where there is much less radiation, liquid water is scarce because it is solidified! The ecology of our planet is caught 'between the frying pan and the freezer'!

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Ex.2. Comprehension check-up.

1.How are different kinds of organism distributed in environments?

2.What is the climate determined by?

3.What is the radiation responsible for?

4.Is the solar radiation distributed evenly across the surface of the earth?

5.Are environments homogeneous on our planet? What does a character of environment depend on?

6.What makes our planet special? Is there any correspondence between the temperatures at its surface and the form of water it exists there?

7.What helps to redistribute water on the surface?

8.How has geological history interacted with climatic change in the history of our planet?

9.How does it happen that liquid water is absent from the environment, near the poles for example, for most of the time?

10.What do the biological activities on the planet depend on and limited by?

11.How can the intensity of radiation act in opposing ways?

Ex. 3. Tell your partner what you have learnt from the article.

Reading B

Ex.4. Read the article and be ready to answer the following questions:

1.If a planet like earth was inhabited by one sort of organism, what kind might it be?

2.Is it possible to find all existing species on the earth everywhere?

3.What does the way of looking for correlations between the biology of different species and the nature of the environment in the special places in which each is found emphasize?

The diversity of organisms and the patchiness of their distribution

It is not too difficult to imagine a planet like earth that is inhabited by just one sort of organism. It might be limited in its distribution to just a very tiny subset of the multiplicity of environments. It might range widely over many physical environments if it possessed broad temperature tolerance. It could range even more widely if it could tolerate periods of desiccation, and even further if it could also function when immersed in water. But, it could live only where there was liquid water, a source of energy and access to inorganic resources for growth. (When, or if, it died it would need to be self decomposing and release its components back to the environment, otherwise it would exhaust its resources and become extinct leaving undecomposed bodies littering the habitat). Even one such 'ideal' organism would give the planet an ecology and a biogeography. A visiting ecologist would find plenty to keep himself

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busy, studying the relationships between this unique organism and its environment. In fact, of course, the earth is inhabited by a multiplicity of types of organism that are neither distributed randomly nor as a homogeneous mixture over the surface of the globe.

Any sampled area, even on the scale of a whole continent, contains only a subset of the variety of species present on earth. These restricted patterns of species distribution occur despite the fact that individuals (or the progeny) of all species are capable of some dispersal, and, for many, dispersal may be on an intercontinental scale (e.g. birds and the seeds of orchids). A great part of the science of ecology tries to explain why every type of organism does not live everywhere. One of the greatest of all ecological generalizations is that all species are always absent from almost everywhere.

It is natural to look for correlations between the biology of different species and the nature of the environment in the special places in which each is found. This approach emphasizes the ways in which the peculiar biologies of different species 'match' the features of the environments in which they live. We try to explain not only how the properties of different sorts of species make their life possible in particular environments, but also to explain their failure in others. A further task of the ecologist is to try to explain how the diversity of organisms has evolved. One of the greatest of ecologists, Evelyn Hutchinson, pointed out that ecology provides the theatre in which the evolutionary play is performed and asked the tantalizing question 'Why are there so many sorts of animal?'

Reading C

Ex.5. Look through the article and say why the word ‘ abaptation’ is considered to be a better word than ‘ adaptation’ to describe the match between organisms and environment.

Natural selection: adaptation or abaptation?

The phrase that, in everyday speech, is most commonly used to describe the match between organisms and environment is;" 'organism X is adapted to' followed by a description of the conditions where the organism is found. Thus, we often hear that 'fish are adapted to live in water', or 'cacti are adapted to live in conditions of drought'.

Unfortunately, biologists use the words 'adapted' or 'adaptation' to mean various. quite different things. The word 'adaptation' implies that the way that organisms react to present circumstances, prepares them for the future, is predictive and implies some sort of forward planning. But, organisms are not designed for, or matched to or fitted to, the present or the future—their character or properties are entirely consequences of the past—they reflect the successes and failures of ancestors. Abaptation (or exaptation) would be a better word than adaptation because its etymology brings the

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implication that the aptness (match) of organisms for their environment is a product of their past rather than a programme for the future. The properties of organisms appear to be apt for the environments that they live in at present only because present environments tend to be similar to those of the past.

An individual will survive, reproduce and leave descendants in some environments but not in others. This is the sense in which nature may be loosely (and anthropomorphically) thought of as selecting. It is in this sense that some environments may be described as favourable or unfavourable, and it is in this same sense that some organisms can be considered to be fit or not. If, because some individuals leave more descendants than others the heritable characteristics of a population change from generation to generation, then evolution by natural selection is said to have occurred.

Of course, the present properties of an organism have not all been selected in the type of environment in which it now lives. Over the course of its evolutionary history (its phylogeny) an organism's remote ancestors may have been single-celled aquatic eukaryotes, and as its evolutionary pathway has led to the present specialized organism—peacock, orchid, shrimp or elephant—it has accumulated some, and shed other properties that it acquired in its evolutionary progress. This baggage of evolutionary history places limits on, and constrains, future evolution and much of what we now see as precise matches between an organism and its environment are either these inherited constraints (e.g. that koala bears can live only on Eucalyptus foliage), or detailed fine-tuning.

Ex.6. Render the sentences into English and pay attention to the translation of the ones, where such words as: one, it are their subjects:

1.Экологи имеют дело с организмами и окружающей средой. Важно понимать взаимосвязь между ними.

2.Необходимо знать, что различия в окружающей среде определяются, главным образом, различиями в количестве солнечной радиации, поступающей в разные части земли, топологией и природой ее геологических образований.

3.Известно, что биологическая активность на Земле вызвана энергией, высвобождаемой в результате неорганических преобразований, таких как, например, окисление различных химических соединений. Однако также очевидно, что основной поток биологической активности на Земле зависит от солнечной энергии, фиксируемой в процессе фотосинтеза.

4.Можно представить экологию нашей планеты зажатой между горячей сковородкой и морозильником.

5.Земля заселена различными типами организмов, которые неоднородно расселены по поверхности земного шара, и совершенно естественно искать соответствие между биологией различных видов и природой окружающей среды в том месте, где вид обнаружен.

6.Понятно, что настоящие свойства организма проходили отбор не в той среде, в которой он сейчас обитает.

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Эволюционная история накладывает ограничения на будущую эволюцию и многое из того, что мы сейчас видим как точное соответствие между организмом и его окружающей средой, является или унаследованными свойствами, или приспособлением до мельчайших деталей.

Unit 3

Grammar:

Passive Voice

Ex.1. Read the sentences. Render them into Russian paying attention to the Passive form of the predicates:

1.The book is aimed at all those whose degree programme includes ecology.

2.Very little is known about the flora of previous interglacial periods.

3.The cultivated form has been selected to produce large seeds which are easily harvested.

4.Both convergent and parallel evolution are often recognized by striking visual resemblances.

5.The number of biomes that are recognized differs between biogeographers, and it is rather a matter of taste how many should be recognized.

6.Millions of people are killed each year by various types of infection and many millions more are debilitated or deformed.

7.When the effects of parasites on domesticated animals and crops are added to this, the cost in terms of human misery and economic loss becomes incalculable.

8.The disagreement needs to be resolved by carefully designed and controlled experiments.

9.Leaves on plants that carried a population of ants lived nearly 1.8 times as long as those on plants from which ants had been deliberately removed.

10.Every organism can be truly represented only by its whole life history.

11.Pest control could be described as having twin aims: controlling the pest and minimizing the disturbance to other species in the community.

12.A community can be defined at any size, scale or level within a hierarchy of habitats.

Word study

Ex.1. Read the words. Give their Russian equivalents:

Analogous, homologous [hɔ’mɔləgəs], convergent, reptiles, metabolism, phylogeny [failəu’ʤeni], phylogenetic [,failəuʤi’netiK] – филогенетический (adj.),

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radiation, placental – плацентарный, evolutionist, biome, biogeographer, flora, fauna, continental tropics, phosphoras, chemical composition

Ex. 2. Translate the following words and word combinations:

A match between; a similarity in form and behavior;	similar environment;		belonging
to different phyletic (филетические ветви) lines;	far removed from each other;
convergence of form; to conceal profound differences;		selective forces;	the same
property; acquired from; evolutionary origins;	to	gain access to;	supporting

tissues;	evolutionary pathways; related groups;		set of constraints and potentials; a
common	ancestral line;	to excavate burrows; to occupy the areas; massive
movements; mineral input;		nutrient-rich waters;	this accounts for; phylogenetically
related groups

Ex.3. Words to be remembered:

Evidence, to belong to, internal structure, mammals, carnivores, to indicate, plants, vegetation, ecological niche, resemblance, larvae, grazing herbivore, guild ( a group of species that exploit the same class of environmental resources in a similar way), lifestyle, drought desert, extend, evaporate, rainforest, abundant, to distinguish, coniferous forests, precipitation, evaporation, to absorb, mineral nutrients, dilute, estuaries, land drainage, water catchments, to inhabit

Reading A: CONVERGENTS AND PARALLES

Notes to the Text:

Convergent evolution – конвергентная эволюция (the process by which organisms of different evolutionary lineages come to have similar form or behavior)

Placental – плацентарный (mammals which develop a persistent placenta; i.e. all mammals other than marsupials and monotremes)

Marsupial [ma:’sju:pjəl] – сумчатый

Monotreme - одноапертурный (a primitive mammal belonging to one of only three genera, laying eggs but having hair and secreting milk)

Parallel evolution - the evolution along similar lines of systematic groups that had been separated geographically at an earlier stage in their history.

Bandicoot – сумчатый барсук

Canopy – покров [‘Kænəpi] Nitrogen - азот [‘naitrəʤən]

Ex.1. Read the text and be ready to explain what convergent and parallel evolution is:

A match between the nature of organisms and their environment can often be seen as a similarity in form and behaviour between organisms living in a similar

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environment, but belonging to different phyletic lines (i.e. different branches of the evolutionary tree). Such similarities also undermine further the idea that for every environment there is one, and only one, perfect organism'. The evidence is particularly persuasive when the phyletic lines are far removed from each other' and when similar roles are played by structures that have quite different evolutionary origins, i.e. when the structures are analogous (similar in superficial form or function), but not homologous (derived from an equivalent structure in a common ancestry). When this is seen to occur, we speak of convergent evolution. Large swimming carnivores have evolved into four quite distinct groups: amongst fish' reptiles, birds and mammals. The convergence of form is remarkable because it conceals profound differences in internal structures and metabolism, indicating that the organisms are far removed from each other in their evolutionary history. Many flowering plants use the support of others to climb high and so gain access to more light than if they depended on their own supporting tissues. The ability to climb has evolved in many different families, and quite different organs have become modified into climbing structures: they are analogous structures but not homologous. In other plant species the same organ has been modified into quite different structures with quite different roles: they are therefore homologous, although they may not be analogous.In this case we can argue that similar selective forces have acted so that the same property has been acquired from quite different evolutionary starting points. A comparable series of examples can be used to show the parallels in the evolutionary pathways of phylogenetically related groups..

The classic example of such parallel evolution is the radiation amongst the placental and marsupial mammals. Marsupials arrived on the Australian continent in the Cretaceous period (around 90 million years ago), when the only other mammals present were the curious egg-laying monotremes. An evolutionary process of radiation then occurred that in many ways accurately paralleled what occurred in the placental mammals on other continents. The subtlety of the parallels in both the form of the organisms and their lifestyle is so striking that it is hard to escape the view that the environments of placentals and marsupials contained 'ecological niches’ into which the evolutionary process has neatly 'fitted' ecological equivalents. (It is important to remember that, in contrast with convergent evolution, the marsupials and placentals started their radiative evolution with an essentially common set of constraints and potentials because they sprang from a common ancestral line.)

Both convergent and parallel evolution are often recognized by striking visual resemblances. The marsupial bandicoot looks rather like a placental rabbit (the long ears make the resemblance particularly striking), and both species excavate burrows, but the bandicoot is largely carnivorous, feeding on insect larvae, whilst the rabbit is a herbivore. By contrast, kangaroos and sheep look remarkably different although both are large grazing herbivores which, when they live side-by-side, have very similar diets. The kangaroo and the sheep are members of the same guild (a group of species that exploit the same class of environmental resources in a similar way), but they look very different. The rabbit and the bandicoot look very similar, but belong to quite different guilds. An ecologist looks for the match of organisms to their

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environment in their lifestyle (e.g. what they feed on and what feeds on them), and an evolutionist emphasizes their phylogeny.

Ex.2. Comprehension check-up:

1.How can a match between the nature of organisms and their environment be seen?

2.In what case do we speak of convergent evolution?

3.Why do fish, birds and mammals belong to convergents?

4.Are organs in plants, modified into climbing structures, called analogous or homologous?

5.How do the parallels differ from convergents?

6.Can you give example of parallel evolution?

7.How is it possible to explain the striking subtlety of the parallels in the form and lifestyle of organisms?

8.What’s the difference of the scientific approach of an evolutionist and ecologist looking for the match of organisms to their environment?

Ex.3. Tell your partner what an ecologist should know looking for the match between organisms and their environments.

Reading B: Patterns in Community structure

Ex.1. Read and answer the following questions:

1.Why is it important for ecologist to consider ‘biomes’ ?

2.How many biomes are there in the world?

3.What factors influence the biological activity of the oceans?

4.How can the concentration of many of the world’s fisheries be explained?

5.Where do freshwater biomes occur?

6.What does the chemical composition of the water depend on?

7.How do salt lakes develop?

8.Do the differences between biomes help to recognize an exact difference of the communities of organisms?

Before examining the differences and similarities between communities it is important to consider the larger groupings, ‘biomes’, in which biogeographers recognize marked differences in the flora and fauna of different parts of the world. These biomes occupy the areas between the frozen wastes of the polar regions and mountain tops and the drought deserts of the continental tropics. They extend from regions that are too dry because most of the water is frozen, to regions that are too dry at some seasons because water evaporates too fast. In tropical rainforest, both liquid water and radiation are usually abundant.

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The number of biomes that are recognized differs between biogeographers, but it is possible to distinguish and describe eight terrestrial biomes: Tundra, Taiga, Temperate forests, Grassland, Chaparral, Deserts, Tropical rainforests, Northern coniferous forests and two aquatic biomes: marine and freshwater. The oceans cover about 71% of the earth’s surface and reach depths of more than 10000m. They extend from regions where precipitation exceeds evaporation to regions where the opposite is true. There are massive movements within this body of water that prevent major differences in salt concentrations developing (the average concentration is about 3%). Two main factors influence the biological activity of the oceans. Photosynthetically active radiation is absorbed in its passage through water and so photosynthesis is confined to the surface region. Mineral nutrients, especially nitrogen and phosphorus, are commonly so dilute that they limit the biomass that can develop. Shallow waters (e.g. coastal regions and estuaries) tend to have high biological activity, because they receive mineral input from the land and less incident radiation is lost than in passage through deep water. Intense biological activity also occurs where nutrient-rich waters from the ocean depths come to the surface; this accounts for the concentration of many of the world's fisheries in Arctic and Antarctic waters.

Freshwater biomes occur mainly on the route from land drainage to the sea. The chemical composition of the water varies enormously, depending on its source, its rate of flow and the inputs of organic matter from vegetation that is rooted in or around the aquatic environment. In water catchments where the rate of evaporation is high, salts leached from the land may accumulate and the concentrations may far exceed those present in the oceans and form brine lakes or even salt pans in which little life is possible. Even in aquatic situations liquid water may be unavailable, as is the case in polar regions.

The differences between biomes allow only a very crude recognition of the sorts of differences and similarities that occur between communities of organisms. Within biomes there are both smalland large-scale patterns of variation in the structure of communities and in the organisms that inhabit them. It has proved quite difficult to devise ways in which even very obvious similarities and differences between communities can be described and measured.

Ex.2. Try to say in a few sentences what you have learnt about biomes and how the knowledge of differences between them helps to examine the communities’ structure.

Reading C: The ‘Life form’ spectra of communities

Ex.1. Read and summarize the article according to the following questions:

1.Why isn’t it easy to compare two areas from ecological point of view according to a list of the names of species present in them?

2.What could Raunkiaer’s way of plant forms classifications reveal and demonstrate?

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3. What did an attempt to classify the ecological diversity of mammalian faunas give ecologists?

In the vast majority of cases, natural communities contain a spectrum of life forms and biologies. A consequence of evolutionary divergence is that taxonomically closely related species may live in different environments. A consequence of evolutionary convergence is that taxonomically unrelated species may live in the same environment. For these two reasons a list of the names of species, genera or even families present in two areas may tell us virtually nothing about how similar the areas are ecologically.

However, serious attempts have been made to develop and refine the ways in which the life and form of higher plants can be described, irrespective of their taxonomy and systematics. Still the simplest, and in many ways the most satisfying, classification of plant forms that disregards their systematics is that of the Danish botanist Raunkiaer (1934). He emphasized that the growth of higher plants depends on the initiation of tissues at apices (meristems), and he classified plants according to their ‘life forms’ defined by the way in which these meristems were held and protected.

The relative frequency of different life forms is then used to construct spectra from the flora of different regions. He compared these with a 'global spectrum' obtained by sampling from a compendium of all species known and described in his time (the lndex Kewensis), biased by the fact that the tropics were, and still are, relatively unexplored. Striking differences between vegetation types are exposed in this way which demonstrate not only matches of organisms to environments but of whole community complexes.

Raunkiaer's methods are clearly a step on the way to a definitive analysis of the ecological diversity of communities, and attempts have been made to improve Raunkiaer's methods, to quantify the ecological diversity (life-form spectra) of mammalian fauna.l

They classified the mammals of forest communities in Malaya, Panama, Australia and Zaire according to their means of locomotion: (i) aerial (bats and flying squirrels); ii) arboreal (species found on small branches in the upper canopy, e.g. primates); iii) scansorial (clawed species of large branches such as squirrels); and (iv) small round mammals (species living mainly on the ground, although coming a little way into the lower canopy). They also classified the mammals according to their feeding habits: (i) plant eaters (herbivores and fruit eaters (fructivores); (ii) insectivores; (iii) carnivores and (iv) mixed feeders. The percentages of species falling into the various categories were then presented in graphical form as 'life-form' spectra. The spectra from the four continents are strikingly similar. Particularly remarkable is the very close similarity of the ecological diversity spectra for the Australian and Malayan forests, bearing in mind that the fauna of Australia is marsupial and that of Malaya is placental. This is a spectacular confirmation that the parallel evolutionary divergence within marsupial and placental phylogenies has resulted in ecologically matched faunas.

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Ex.3. Render the article in English using the words below:

1.Сосуществующие виды обычно несколько различаются, но каждый соответствует своей среде и живет в ней своей жизнью, т.к. среда – гетерогенна (разнородна).

2.Разница в экологии видов, существующих в пределах одного сообщества, заметнее, когда виды родственны, т.к. эти различия наиболее четко проявляются на фоне общих черт. Однако необходимо понимать особенности сосуществования членов, по крайней мере, одной гильдии, которые необязательно должны находиться в близком родстве.

Например, рачок-криль является богатым пищевым ресурсом для тюленякрабоеда и морского леопарда Антарктики, а также поедается кальмаром, рыбой, птицами, китами и поэтому полный анализ соответствия между составными загадки существования такого сообщества должен учитывать не просто определенную таксономическую группу, а все гильдии в целом.

3.При исследовании группы систематически соотнесенных видов неправильно рассматривать каждый вид как независимый продукт естественного отбора. Сходство между видами, возможно, возникло в процессе конвергентной эволюции или как результат наличия общих предков. Пример с тюленем и другие подобные примеры ставят больше вопросов, чем ответов, и ни на один вопрос нельзя сегодня ответить однозначно.

Coexisting species; to differ in subtle ways; to match environment; a style of life; heterogeneous; closely related; relevant differences; against a background; common features; the same guild; krill; an abundant resource; Antarctic waters; crabeater-seal; leopard seal; to specialize on; squid; whale; jigsaw puzzle; take into account; taxonomic group; whole guilds; systematically related species; as if it has arisen; similarities; ancestors in common; to provide questions; a straightforward answer.

Unit 4

Grammar:

Degrees of Comparison

Ex.1. Translate the following sentences. Pay attention to the translation of the degrees of comparison.

1.The differences are less striking than the resemblances.

2.A mammal, that changes the thickness of its coat as a reaction to cold weather, may start to develop the thicker coat in advance of the event.

3.Where two species have evolved a mutual dependence, the fit may be even tighter.

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4.Most of the more obvious heterogeneities in a population arise only when parts become isolated geographically.

5.No environments are constant, but some are more constant than others.

6.Mutualisms are represented in a much more varied range of species interactions than competition, predation and parasitism.

7.The records of climatic change in the tropics are far less complete than those for temperate regions.

8.A different interpretation is that the present distributions are relicts of populations once distributed more widely.

9.The balance between birth rate and death rates is as important for the determination of species abundance and distribution as a species ability to disperse.

10.Organisms have lived in environments that were not quite the same as at present.

Word Study
Ex.1. Read the words. Find their Russian equivalents.
Homogeneity [hɔməuʤe’ni:iti]; genetic;	heterogeneity [hetərəuʤi’ni:iti];
reproduction; recombination; genotypes; gene,	gamete	[‘gæmi:t] –	половые
клетки; transplant [træns’pla:nt]; hydroid – гидроид; crab,		daily cycle;	mobile;
dramatic.

Ex.2. Translate the following words and word combinations:

Genetic exchange; isolated geographically; forces of natural selection; locally favored genotypes; to be at an advantage; gene flow; the same species; specialized races; become differentiated - видоизмененным, дифференцированным; unfavorable environment; higher plants; to have freedom; to search out resources; vagaries of passive dispersal; to tolerate life in two extremes; shore-feeding birds; to oscillates between; to move with the tides.

Ex.3. Words to be remembered:

To interbreed; to eliminate; exchange; mobility; to override; to arise; obvious; to

occur; to remain; to depend on; sessile organisms; pollen; seeds;	motile; seaweed;
to settle; to escape from; to uproot itself – искоренять;
algae [‘ælʤi: -pl. ]; alga – [‘ælgə] - морская водоросль;	seashore; fixed
organisms; shrimp –мелкие креветки; tides; descendant;
to hazard [‘hæzəd] – рисковать; mussel – мидия; tolerance

Reading A: SPECIALIZATION WITHIN SPECIES

Notes to the text:

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Moss – мох

Lethal [‘li:Ѳəl] – фатальный, смертоносный

Sponge - губка; губки –pl.

Barnacle – морская уточка (ракообразное)

Ex. 1. Read and explain the contrast between the ways in which mobile and fixed organisms ‘match’ their environment:

The homogenizing effects of genetic exchange (and recombination) tend to mean most of the more obvious heterogeneities in a population rise only when become isolated geographically and cease to interbreed. However, if the local forces of natural selection are very powerful, they can override the homogenizing forces of sexual reproduction and recombination. Then, even where there is some interbreeding, locally favoured genotypes may be at such an advantage that illfavoured combinations are continually eliminated. Gene flow continues to occur, populations remain part of the same species, but local specialized races appear within it. The exchange of genetic material through a population depends on the mobility of whole organisms or, in the case of sessile organisms, on the mobility of gametes, pollen or seeds.

Local, specialized populations become differentiated most conspicuously amongst organisms that are sessile for most of their lives. Motile organisms have a large measure of control over the environment in which they live; they can recoil or retreat from a lethal or unfavourable environment and actively seek another. However, the sessile higher plants, for example moss, seaweed and coral, have no such freedom. After dispersal they must live, or die, in the conditions where they settle. The most that a higher plant can do is to search out resources or escape from an unfavourable site by growing from one place to another; it can never uproot itself and choose to transplant itself elsewhere. Its descendants (seeds, pollen or gametes) are hazarded to the vagaries of passive dispersal on the wind or water, or in or on the bodies of animals. Populations of non-mobile organisms are therefore exposed to forces of natural selection in a peculiarly intense form.

The contrast between the ways in which mobile and fixed organisms 'match' their environment is seen at mostly on the seashore, where the intertidal environment continually oscillates between being terrestrial and being aquatic. The fixed algae, hydroids, sponges, mussels and barnacles all meet and tolerate life in the two extremes. But, the mobile members of the community, for example the shrimps, crabs and fish, travel with and track their aquatic habitat as it moves, whilst the shorefeeding birds move back and forth, following the advance and retreat of their terrestrial habitat. The fixed organisms have to tolerate the whole daily cycle of change in their environment, but those that are mobile have no need for such tolerance—they move with the tides. There is a sense in which the match of such mobile organisms to their environment enables them to escape many of the forces of natural selection. Mobility enables the organism to match its environment to itself. The immobile organism must match itself to its environment.

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Ex.2. Comprehension check-up:

1.When do obvious heterogeneities in a population arise?

2.In what case can locally favored genotypes override the homogenizing effects of genetic exchange?

3.What does the exchange of genetic material through a population depend on?

4.Which organisms have more control over the environment in which they live: motile or sessile ones?

5.Why are populations of fixed organisms exposed to selective forces in more intense form than mobile ones?

6.How are mobile organisms of the seashore able to escape the forces of natural selection?

7.How do mobile organisms differ from immobile ones in their efforts to ‘match’ their environment?

Ex.3. Summarize the article and tell what you have learnt about the specialization within species.

Reading B: The match of organisms to varying environments

Notes to the text: Erratic – неустойчивый

Hurricane [‘hʌriKən] – ураган Cyclone [‘saiKlɔun] –циклон

Onset – натиск, начало Cue – сигнал, намек

Phenotype [finɔtaip] – фенотип

Ecotype – a subset of individuals within a species with a characteristic ecology

Ex.1. Read the article consulting a dictionary:

The word ‘ecotype' was first coined for plant population to describe genetically determined differences between populations within a species that reflect local matches between the organisms and their environments. The existence of different ecotypes within a species was demonstrated by transplanting plants from a variety of natural habitats into a common habitat, and allowing them to develop through one or more growing seasons. It is essential in such studies that the plants from the different places of origin should be grown and compared in the same environment.

No environments are constant over time, but some are more constant than others. No form or behaviour of an organism can match a changing environment unless it too changes. Three major categories of environmental change can be recognized.

1 Cyclic changes—rhythmicly repetitive, like the cycles of the seasons, the move-

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ments of the tides and the light and dark periods within a day.

2 Directional changes—in which the direction of a change is maintained over a period that may be long in relation to the life span of the organisms that experience it. Examples are the progressive erosion of a coastline, the progressive deposition of silt in an estuary and the cycles of glaciation.

3 Erratic change—this includes all those environmental changes that have no rhythm and no consistent direction, for example the erratic course and timing of hurricanes and cyclones, flash storms and fires caused by lightning.

The optimal fit of organisms to varying environments must involve some compromise between matching the variation and tolerating it.

There are two main ways in which organisms time their responses to cyclic changes in their environment: (i) by changing in response to the environmental change; or (ii) by using a cue that anticipates the change.

If the cycle in conditions is weak and contains much variation, the organisms may best match the changing conditions by responding to them directly.

There is, however, a disadvantage, a price to be paid by organisms that respond directly to environmental change. A mammal that changes the thickness of its coat as a reaction to the weather becoming cold will have to shiver until the process of replacing its coat has taken place. But, if it reacts not to the onset of cold, but to an environmental cue that is correlated with, and therefore predicts, the onset of cold, such as the shortening of day length, it may start to develop the thicker coat in advance of the event. The use of such cues is common among animals that live in environments with a strong and repeated cycle of environmental change, and where the variation in the cycle is relatively weak.

For an organism that cannot run away from adverse conditions, seasonal changes in its form may be the most effective solution to problems of survival in a changing environment. In arid environments, somatic polymorphism may be even more extreme than in the case of aquatic plants. Some species produce three crops of leaves within 1 year, each of different morphology.

Ex.2. Comprehension check-up:

1.What is the word ‘ecotype’ used to describe?

2.Is it possible for an organism to match a changing environment without changing itself?

3.What must the optimal fit of organisms to varying environments involve?

4.How do organisms time their responses to cyclic changes in their environment?

5.In what case do organisms match the changing conditions by responding to them directly?

6.What is the best way to survive in a changing environment for an organism that cannot run away from adverse conditions?

Ex.3. Work with a partner. Ask and answer questions in English according to the text and check your partner: student A and student B.

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Student A:

1.Что означает слово ‘ экотип’?

(It is used for plant populations to describe genetically determined differences between populations within a species that reflect local matches between the organisms and their environments)

2.Может ли организм иметь совместимость с изменяющейся окружающей средой, не изменяясь сам?

(No form of an organism can match a changing environment unless it too changes.)

3.Что должно подразумевать наиболее оптимальное соответствие организмов изменяющимся средам?

(It must involve some compromise between matching the variation and tolerating it)

4.Как организмы реагируют на цикличные изменения в окружающей среде?

(There are two main ways in which organisms time their responses to cyclic changes in their environment: 1. by changing in response to the environmental change; 2. by using a cue that anticipates the change. The use of such cues is common amongst both plants and animals that live in environments with a strong and repeated cycle of environmental change, and where the variation in the cycle is relatively weak.)

5.В каком случае организмы приспосабливаются к меняющимся условиям, непосредственно реагируя на них?

(If the cycle in conditions is weak and contains much variation, the organisms may best match the changing conditions by responding to them directly)

6.Как организм может выжить в меняющейся среде, если не может спастись от неблагоприятных условий?

(For an organism that cannot run from adverse conditions, seasonal changes in its form may be the most effective solution to problems of survival in a changing environment.)

Student B:

1. (What does the word ‘Ecotype’ mean?)

Впервые это слово применили для популяций растений в описании генетически детерминированных различий между популяциями в рамках одного вида, которые отражают соответствия между организмами и их средами на определенном уровне.

2. (Is it possible for an organism to match a changing environment without changing itself?)

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Ни один вид организма, его поведение не может соответствовать изменяющейся среде, если он сам при этом не изменяется.

3. (What must the optimal fit of organisms to varying environments involve?)

Оно должно подразумевать некоторый компромисс между противостоянием изменению и способностью эти изменения перенести.

4.(How do organisms time their responses to cyclic changes in their environment?)

Они это делают двумя способами: 1. изменяя свою реакцию на изменение в окружающей среде или 2. реагируя на различные сигналы природы, которые предупреждают о наступлении такого изменения. Учет таких сигналов распространен среди как растений, так и животных, которые живут в среде с явно выраженным и повторяющимся циклом изменений окружающей среды и где отклонения в цикле относительно слабы.

5.(In what case do organisms match the changing conditions by responding to them directly?)

Если в цикле много отклонений, то организмы лучше всего вживаются в условия, непосредственно реагируя на них.

6.(What is the best way to survive in a changing environment for an organism that cannot run away from adverse conditions?)

В таком случае сезонные изменения в его форме могут оказаться наиболее эффективным решением проблем выживания в меняющейся окружающей среде.

Reading C: Pairs of species

Ex.1. Read the following article and render it in Russian ( in a written form)

Notes to the text:

Host-specific rust fungi [houst rʌst ‘fʌŋɡai] – ржавчинные грибы, специфичные по отношению к хозяину

Leguminous plant [le’ɡju:minəs] – бобовые растения insect pollinator – насекомое-опылитель

herbicide [‘hə:bisaid] - гербицид one and for-all – навсегда

Some of the most strongly developed matches between organisms and their environment are those in which one species has developed a dependence upon another. This is the case in many relationships between consumers and their foods, such as the dependence of koala bears on Eucalyptus foliage or giant pandas on bamboo shoots, whole syndromes of form, behaviour and metabolism constrain the

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animal within its narrow food niche, and deny it access to what might otherwise appear suitable alternative foods. Similar tight matches are characteristic of the relationships between some parasites and their hosts. For example, the host-specific rust fungi fit narrow and precisely defined environments: their unique hosts.

Where two species have evolved a mutual dependence, the fit may be even tighter. The mutualistic association of nitrogen-fixing bacteria with the roots of leguminous plants, and the often extremely precise relationship between insect pollinators and their flowers are two good examples. The closest matches between organisms and their environments have evolved where the most critical factor in the life of one species is the presence of another: the whole environment of one organism may then be another organism.

When a population has been exposed to variations in the physical factors of the environment, for example a short growing season, a high risk of frost or drought or the repeated application of a herbicide, a once-and-for-all tolerance may ultimately evolve' The physical factor cannot itself change or evolve as a result of the evolution of the organisms. By contrast, when members of two species interact, the change in each produces alterations in the life of the other, and each may generate selective forces that direct the evolution of the other. In such a coevolutionary process the interaction between two species may continually escalate. What we then see in nature may be pairs of species that have driven each other into ever-narrowing ruts of specialization—an ever-closer match.

Unit 5

Grammar:

Continuous tenses

Ex. 1. Translate the following sentences:

1.Environments are still changing and the matching of organisms to their environments will always lag behind.

2.There are certain combinations of conditions and resources which can allow a species to maintain a viable population, but only if it is not being adversely affected by enemies.

3.A plant may be said to compete with another for a space in a canopy, this means that plants are competing for the light that might be captured in that space.

4.Censuses can be made only with the very greatest difficulty, except when the animals are moving above ground and can be trapped.

5.It is becoming realized that migration can be a vital factor in determining and regulating abundance.

6.On older leaves, the aphides may be becoming extinct as the leaf dies.

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7.In western Europe by 1985, around 500 million individuals of each species were being produced for release each year.

8.The world is changing. Things never stay the same.

9.Ecological communities are non-uniform, continually altering and subject to the statistical events of random change.

10.The reason why simple laws are difficult to perceive in ecology is that the patterns keep changing; organisms are heritably variable and evolve, and thus, at least, some of the rules of behavior and interaction themselves change.

11.The assumption is that when competition is operating and resources are limited, one species will inevitably exclude another.

Word study

Ex.1. Read the words. Give their Russian equivalents:

Colonize, techniques, structure, dioxide, stage, exploit, extreme, cyclone, catastrophes, physiological, migration, resources, reproduction, variation, concentration, volcanoes, activity of enzyme [‘enzaim], storms, zinc;

Ex.2. Translate the following words and words combinations:

Effects of environmental conditions; relative humidity; the concentration of pollutants; destructive storms; under conditions, measures of fitness; the respiration rate of a tissue; the growth rate of individuals; response to a condition; alkaline conditions; the earth is tilted; this drives temperature differentials; daily hazards; to hold fast to the rocks; forces of the waves and tides; disasters strike natural communities; detailed accounts of; wind velocity; undisturbed communities; continual natural gaps; enormously damaging natural occurrences; volcanic eruption; an ecological risk analysis; valuable to ecologists

Ex.3. Words to be remembered:

Resources; to require; rate of birth; migration; interaction; aquatic communities; turbulence; survivorship; reproduction; physiological state; adverse level; acid conditions; latitudinal variation; heat damage; long-term prediction; to withstand; to persist; to recur; ancestor; to suffer; to devastate; gust; regeneration; destruction

Reading A: CONDITIONS

Ex.1. Read the article and think about the influence of environmental conditions on the distribution and abundance of a species.

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In order to understand the distribution and abundance of a species we need to know many things: (i) its history; (ii) the resources that it requires; (iii) the individuals' rates of birth, death and migration; (iv) their interactions with their own and other species; and (v) the effects of environmental conditions.

A condition is an abiotic environmental factor which varies in space and time. Examples include temperature, relative humidity, PH, salinity and the concentration of pollutants. The 'conditions' of an environment also include a variety of hazards such as hurricanes and volcanoes and, especially in aquatic communities, destructive storms and turbulence. A condition may be modified by the presence of other organisms, for example temperature, humidity and soil pH may be altered under a forest canopy. But, unlike resources, conditions are not consumed or used up by organisms.

For some conditions we can recognize an optimum concentration or level at which an organism performs best, with its activity tailing off at both lower and higher levels. For an evolutionary ecologist 'optimal' conditions are most likely to be those under which the individuals of the species leave most descendants (are fittest), but these are often quite impossible to determine in practice because measures of fitness should be made over several (ideally many) generations. Instead, we more often measure the effect of conditions on some chosen properties like the activity of an enzyme, the respiration rate of a tissue, the growth rate of individuals, their rate of reproduction or survivorship or on physiological states. However, the effect of variation in conditions on these various properties will often not be the same.

The precise shape of the curve of response to a condition—whether it is symmetrical or skewed, broad or narrow—will vary from condition to condition' The generalized form of response is appropriate for conditions like temperature and pH in which there is a continuum from an adverse or lethal level (e.g. freezing or very acid conditions), through favourable levels of the condition to a further adverse or lethal level (heat damage or very alkaline conditions). A particular problem arises at very high temperatures which may increase the activity of enzymes but also the rate at which they become inactivated. A very short exposure to high temperature may then increase an activity but a longer exposure may be lethal.

Variations in temperature on and within the surface of the earth have a variety of causes: the effects of latitude and altitude, continental, seasonal and diurnal effects, microclimatic effects and, in soil and water, the effects of depth. Latitudinal and seasonal variations cannot really be separated. The angle at which the earth is tilted relative to the sun changes with the seasons, and this drives some of the main temperature differentials on the earth's surface. The hottest temperatures occur in the middle latitudes rather than at the Equator.

Ex.2. Comprehension check-up:

1.What is important to know in order to understand the distribution and abundance of a species?

2.What is a condition?

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3.Can you give examples of the condition components of an environment?

4.How do conditions differ from resources?

5.Is condition anything inalterable?

6.What are optimal conditions for an organism?

7.How is it possible to determine the fitness of a species?

8.What is often measured instead of fitness?

9.What will be the effect of variation in conditions on various properties of an organism?

10.How harmful may high temperatures be?

Ex.3. Speak on conditions as variable environmental factors, having influence on the distribution and abundance of a species.

Reading B: Hazards, disasters and catastrophes: ecology of extreme events

Ex.1. Read the following article consulting a dictionary:

The wind and the tides are normal daily hazards in the life of many organisms. Their structure and behaviour bear some witness to the frequency and intensity that such frequent hazards have played in the evolutionary history of their species. Thus, most trees withstand the force of most storms without falling over or losing their living branches. Most limpets, barnacles and kelps hold fast to the rocks through the normal day to day forces of the waves and tides. We can also recognize a scale of more severely damaging forces (we might call them 'disasters'), that occur occasionally, but with sufficient frequency to have contributed repeatedly to the forces of natural selection. When such a force recurs it will meet a population that still has a genetic memory of the selection that acted on its ancestors—and may therefore suffer less than they did. In the woodlands and shrub communities of arid zones, fire has this quality, and tolerance of fire damage is a clearly evolved response. There are clearly also many species of plant and animal whose life depends on opportunistically exploiting 'disasters' that have affected others.

When disasters strike natural communities it is only rarely that they have been carefully studied before the event. One exception is cyclone 'Hugo' which struck the Caribbean island of Guadeloupe in 1994. Detailed accounts of the dense humid forests of the island had been published only 4 years before cyclone 'Hugo'. The cyclone devastated the forests with mean maximum wind velocities of 27O km h-r and gusts of 32o km h-1. Up to 30o mm of rain fell in 40 h. Early stages of regeneration after the cyclone typify the responses of long-established communities on both land or sea to massive forces of destruction. Even in ‘undisturbed' communities there is continual creation of gaps as individuals (e.g. trees in a forest, kelps on a seashore) die and the space they occupied is recolonized. After massive devastation by cyclones or other widespread disasters, much of the recolonization

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follows much the same course as the microsuccessions that were part of the natural regeneration cycle in the previously undisturbed community. Species that normally colonized only natural gaps in the vegetation come to dominate a continuous community. Whether the community is that of a rocky shore or a tropical rainforest the early succession after disasters tends to be of competition- (or shade-) intolerant, relatively short-lived species with high rates of precocious reproduction.

In contrast to conditions that we have called 'hazards' and 'disasters' there are natural occurrences that are enormously damaging, yet occur so rarely that they may have no lasting selective effect on the evolution of the species. We might call such events 'catastrophes', for example the volcanic eruption of Mt St Helens or of Krakatau. The next time that Krakatau erupts there are unlikely to be any genes persisting that were selected for volcano tolerance!

Of course, what we have called ecological hazards, disasters and catastrophes are arbitrary stages on a continuum. It would be valuable to ecologists, to quantify this continuum—the equivalent of an ecological risk analysis. The bulk of statistical theory has, however, been mainly concerned with means and variances, i.e. with the 'normal' range of happenings. Ecologists require a statistical procedure that is appropriate for rare events and it is convenient that the probability structure of extreme values conforms to a generalized distribution that can be estimated by maximum likelihood techniques. Such a statistical procedure has been applied to sea surface temperatures, wave forces, wind speeds and human life spans and accurate long-term predictions can apparently be made from a surprisingly small number of measurements. For the distribution of organisms in nature it is usually extremes rather than averages that matter. The statistics of extreme values is therefore likely to become increasingly valuable to ecologists'

Ex.2. Render the first paragraph in Russian.

Ex.3. Try to explain what role extreme events play in the evolution of species and why their prediction is so valuable to ecologists.

Reading C: Environmental pollution

Ex.1. Read the text and try to understand how individuals can tolerate pollution and become adapted to it.

A number of environmental conditions that are, regrettably, becoming increasingly important are due to the accumulation of toxic by-products of humans' activities.

Sulphur dioxide emitted from power stations, and metals like copper, zinc and lead, dumped around mines or deposited around refineries, are just some of the pollutants that limit distributions, especially of plants. Many such pollutants are present naturally, but at low, concentrations, and some are indeed essential nutrients for

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plants. But, in polluted areas their concentrations can rise to lethal levels and there is a succession of disappearances of one species after another. The loss of species is often the first indication that pollution has occurred and changes in the species richness of a river, lake or area of land provide bioassays of the extent of their pollution.

Yet, it is rare to find even the most inhospitable polluted areas entirely devoid of species; there are usually at least a few individuals of a few, species that can tolerate the conditions. Even natural populations from unpolluted areas often contain a low frequency of individuals that tolerate the pollutant. Such individuals may be the only ones to survive or colonize as pollutant levels rise, and then become the founders of a tolerant population to which they have passed on their 'tolerance' genes. Pollution, therefore, provides us with an ideal opportunity to observe evolution in action. However, sufficient genetic variability is not present in all populations; some species repeatedly give rise to tolerant populations, whilst others rarely if ever do so.

Thus, in very simple terms, a pollutant has twofold effect. When it is newly arisen or is at extremely high concentrations, there will be few individuals of any species present (the exceptions being naturally tolerant variants or their immediate descendants). Subsequently, however, the polluted area is likely to support a much higher density of individuals, but these will be representatives of a much smaller range of species than would be present in the absence of the pollutant' Such newly evolved, species-poor communities are now an established part of human environments.

Pollution can of course have its effects far from the original source. Toxic effluents from a mine or a factory may enter a watercourse and affect its flora and fauna for its whole length downstream. Effluents from large industrial complexes can pollute and change the flora and fauna of many rivers and lakes in a region and cause international disputes. A striking example is the creation of 'acid rain' falling in Scotland and Scandinavia from industrial activities in other countries. Since the Industrial Revolution, the burning of fossil fuels and the consequent emission to the atmosphere of various pollutants, notably sulphur dioxide, has produced a deposition of dry acidic particles and rain that is essentially dilute sulphuric acid. The history of the acidification of lakes is often recorded in the succession of diatom species accumulated in lake sediments.

Diatom species composition, for example, has changed over the past 400 years or more in Round Loch of Glenhead, Scotland — far from major industrial sites. A sediment core containing the accumulated identifiable remains of diatoms has been analyzed section by section, and these show a rapid and dramatic decline in those species that are rarely found below pH 5.5 and at the same time an increase in species typical of acid conditions. Since about 1850 the pH has declined from about 5.5 to about 4.6.

Ex.2. Find in the text equivalents of the following words and word combinations:

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Из-за накопления токсичных побочных продуктов деятельности человека;

сернистый газ,	выбрасываемый	энергетическими станциями;		металлы,
сбрасываемые	вокруг приисков	и шахт;	загрязняющие	вещества,
препятствующие	распространению	видов;	естественно присутствовать в

природе; необходимое питательное вещество; летальный уровень; череда исчезновений видов; видовая насыщенность; дать биологическую оценку; в наибольшей степени загрязненные территории; полностью лишенный видов; наблюдать эволюцию в действии; достаточная генетическая изменчивость; двойной эффект; ядовитые стоки с заводов; попадать в водоток; воздействовать на флору и фауну; вызывать экологические нарушения на международном уровне; образование кислотного дождя; сжигание ископаемого топлива; постоянные выбросы в атмосферу различных загрязнителей; осаждение сухих кислотных частиц; окисление озер; вымирание видов.

Ex.3. Comprehension check-up.

1.What are the origins of environmental pollution?

2.Do pollutants always effect natural populations negatively?

3.In what case does pollution provide us with an opportunity to observe evolution in action?

4.Why do we say that a pollutant has a twofold effect?

5.How far can pollution spread from the original source?

6.How harmful may acid rains be?

Ex. 4. Check your knowledge of the following words and expressions. Then use them discussing the problems of environmental pollution.

Due to accumulation of toxic by-products of humans’ activities; sulphur dioxide emitted from; metals dumped around mines; deposited around refineries; pollutants; limit distribution; present naturally; at low concentrations; essential nutrients; lethal levels; succession of disappearances; loss of species; indication; species richness; provide bioassays; inhospitable polluted areas; entirely devoid of species; at least; tolerate the pollutant; sufficient genetic variability; give rise to tolerant populations; a twofold effect; enter a watercourse; affect flora and fauna; toxic effluents; cause international disputes; creation of acid rain; the burning of fossil fuels; consequent emission to atmosphere; a deposition of dry acidic particles; acidification of lakes; a rapid and dramatic decline in species.

Reading D: The Ecological Niche

Ex.1. Read the following article and think of the question: what does the concept of the ecological niche imply?

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The concept, that is central to much of ecological thinking, the definition of which depends crucially on the responses of organisms to environmental conditions, is that of the ecological niche. The term ‘ecological niche’ has been part of the ecologist’s vocabulary for more than half a century, but for the first 30 years its meaning was rather vague. The current, generally accepted definition, is best illustrated by example. Organisms of any given species can survive, grow, reproduce and maintain a viable population only within certain temperature limits. This range of temperature is the species’ ecological niche in one dimension (i.e. the dimension 'temperature’).

Of course, an organism is not effected by temperature in isolation, nor by any other single condition. Taking temperature and humidity together, the niche becomes two dimensional and can be visualized as an area. If further conditions are brought into consideration (as they should be), then the -next step is a three-dimensional description of the niche, a volume; but the incorporation of more than three dimensions is impossible to visualize. Nevertheless, the process can be continued in an abstract way, by analogy, and a species' true ecological niche can be thought of as an n-dimensional hypervolume within which it can maintain a viable population.

This, in essence, is the niche concept developed by Hutchinson (I957), except that in addition he proposed a separate niche dimension not only for each important environmental condition, but also for each of the resources that the organism requires (e.g. solar radiation, water, mineral nutrients for plants; food, nest sites, etc.). This view is now one of the cornerstones of ecological thought.

Provided that a location is characterized by conditions within acceptable limits for a given species, and provided also that it contains all necessary resources, then the species can, potentially, occur and persist there. Whether or not it does so depends on two further factors. First, it must be able to reach the location, and this depends in turn on its powers of colonization and the remoteness of the site. Second, its occurrence may be precluded by the action of individuals of other species which compete with it or prey on it.

Usually, a species has a larger ecological niche in the absence of competitors and predators than it has in their presence. In other words, there are certain combinations of conditions and resources which can allow a species to maintain a viable population, but only if it is not being adversely affected by enemies. This led Hutchinson to distinguish between the fundamental and the realized niche. The former describes the overall potentialities of a species; the latter describes the more limited spectrum of conditions and resources which allow it to persist, even in the presence of competitors and predators. In common usage the word 'niche' means a position in space. This is not the meaning in ecological science and it is important to recognize that an ecological niche is not something that can be seen. It is an abstract concept that brings together, in a single descriptive term, all of the environmental conditions and resources that are necessary for an organism to maintain a viable population. Nor is it necessary to make measurements along each and every niche dimension for the concept to be useful.

Habitats, by contrast, are actual places, and as such they provide a variety of conditions and resources which may satisfy the requirements (i.e. provide the niches)

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for warblers, oak trees, spiders and myriads of other species. The niches of the species that occur together in any one habitat are likely to be different, sometimes markedly so.

Ex.2. Put questions to the text in order to discuss the problem with your partner. Try to cover all important points in the text which help to understand the concept of the species’ ecological niche.

Unit 6

Grammar:

Gerund

Ex.1. Translate the following words. Pay attention to gerund constructions.

1.The population grows only slowly after colonizing a site.

2.Most trees withstand the force of most storms without falling over or losing their living branches.

3. There are many species of plant and animal whose life depends on opportunistically exploiting ‘disasters’ that have affected others.

4.Changes in vegetation were measured by using optical point cover.

5.It is becoming realized that migration can be a vital factor in determining and regulating abundance.

6.The nature and consequences of some modifications can be understood without going into the details of the mathematics.

7.Perhaps the most serious problem in defining and classifying communities of species is that species are not truly independent points to be used in such an analysis.

8.Each plant and each leaf, by intercepting radiation, creates a resource-depletion zone.

Word Study

Ex.1. Read the words. Give their Russian equivalents.

Ion, molecule [məu’leKjulə], parasites, microflora, solar radiation, metabolic activity, radiant energy, resource, atmosphere, object, fraction, absorbed, photosynthesis;

chemical,	cycle [saiKl], organism,	continuum [Kən’tiŋjuəm],		spectrum,
apparatus	[‘æpə’reitəs], chlorophyll	pigment	[Klɔrəfi], fixation,	successive
stage, fundamental; specialization; decomposition,			chloroplast.

Ex.2. Translate the following words and word combinations:

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to deepen understanding, food resource; trapped in photosynthesis; a web of consumer interactions; flux of radiation; diffused by atmosphere; direct and diffused radiation; to intercept radiant energy; to contribute latent heat; to power the transpiration stream; visible to the human eye;

Ex.3. Words to be remembered:

To adopt; seed; to consume; stuff; to involve; to assemble; successive stage; to reflect; to transmit; to convert; to break down; constraints on something; packages of resources; to contribute to; to absorb mineral nutrients; metabolic activity; reliable resources; flowering; restricted to; to vary; predation; lifetime; waste products; food chain

Reading A: Resources

Ex.1. Read the text and think of the difference between conditions and resources for an organism.

Science adopts many words from common speech, and they can carry with them a cloud of nuances that bear little relation to the science. This is true of words like 'conditions' and 'resources', which have become assimilated into the science of ecology. Yet, the very act of searching for what is meant by a word can deepen understanding. All things consumed by an organism are resources for it: Just as nitrate, phosphate and light may be resources for a plant, so may nectar and a hole in a log be resources for a bee, and so may acorns, walnuts, other seeds, and a larger hole in a log be resources for a squirrel.

But, what is meant by 'consumed? It cannot simply mean eaten (although, nectar and acorns are eaten) nor yet incorporated into biomass (although, this happens to nitrate, nectar and acorns): bees and squirrels do not eat holes nor incorporate them into biomass. Nevertheless, a hole that is occupied is no longer available to another bee or squirrel, just as the atom of nitrogen, the sip of nectar or the mouthful of acorn is no longer available to other consumers.

All these things have been consumed in the sense that the stock or supply has been reduced. Thus, they are resources, not conditions, because they represent quantities that can be reduced by the activity of the organism. The resources of living organisms are mainly the stuffs of which their bodies are made, the energy that is involved in their activities and the places or spaces in which they act out the cycles of their lives. The body of a green plant is assembled from inorganic ions and molecules which represent its food resources, whilst solar radiation, trapped in photosynthesis, provides the energy resource. Green plants themselves represent packages of food resources for herbivores which, in turn, form packages of resources for carnivores. The bodies of organisms also represent food resources for parasites and, when dead, for microflora and detritivores. A large part of ecology is about the assembly of

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inorganic resources by green plants and the reassembly of these packages at each successive stage in a web of consumer interactions. Thinking about resources becomes particularly important when we come to consider how what one organism consumes affects what is available to others (of the same or of different species).

Ex.2. Comprehension check-up.

1.Why do such words as ‘conditions ‘ and ‘resources’ considered as ecological terms, require particularly deep understanding?

2.Why do such things as holes for bees or walnuts for a squirrel represent resources not conditions?

3.What are the resources of living organisms?

4.How are packages of inorganic resources assembled and reassembled at each successive stage in a web of consumer interactions?

5.In what case does it become really important to think about resources?

Reading B: Radiation as a resource

Ex.1. Read the text and find out how solar radiation differs from all other resources.

Notes:

detritivores [dit’raitivərəs] – питающиеся детритом;

carnivorous [Ka:ni:vərəs] – хищные виды, herbivorous – травоядные

Solar radiation is the only source of energy that can be used in metabolic activities by green plants. It differs in many ways from all other resources.

Radiant energy comes to the plant as a flux of radiation from the sun, either directly or after it has been diffused by the atmosphere or reflected or transmitted by other objects. The relative amounts of direct and diffused radiation arriving at an exposed leaf depend on the amount of dust in the air and, in particular, the thickness of the scattering air layer between the sun and the plant. The direct fraction is highest at low latitudes.

When a leaf intercepts radiant energy it may be reflected (with its wavelength unchanged), transmitted (after some wavebands have been filtered out) or absorbed. Part of the fraction that is absorbed may raise the leaf temperature and be reradiated (but now at much longer wavelengths), and part may contribute latent heat of evaporation of water and so power the transpiration stream. A small part may reach the chloroplasts and drive the process of photosynthesis. Radiant energy is converted during photosynthesis into energy-rich chemical compounds of carbon which will subsequently be broken down in respiration (either -by the plant itself or by those that consume it). But, unless the radiation is captured and chemically fixed at the instant it falls on the leaf, it is irretrievably lost for photosynthesis. This is in complete contrast

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to an atom of nitrogen or carbon or a molecule of water that may cycle repeatedly through endless generations of organisms.

Solar radiation is a resource continuum—a spectrum of different wavelengths — but, the photosynthetic apparatus is able to gain access to energy in only a restricted band of this spectrum. All green plants depend on chlorophyll pigments for the photosynthetic fixation of carbon, and these pigments fix radiation in a waveband between 38O and 710 nm (or in broad terms 400-700 nm). This is the band of 'photosynthetically active radiation' (PAR). It corresponds broadly with the range of the spectrum visible to the human eye that we call ‘light’. About 56% of the radiation incident on the earth’s surface lies outside the PAR range and is unavailable as a resource for green plants. In other organisms there are pigments that operate in photosynthesis outside the PAR range of green plants. However, the chlorophyll pigments of green plants put fundamental constraints on the radiation that green plants can use as a resource, and so also constrain how much energy they contribute to the community in which they live.

Ex. 2. Comprehension check-up.

1.How does radiant energy reach green plants?

2.What happens to radiant energy when it is intercepted by a plant leaf?

3.How is radiant energy converted during photosynthesis?

4.Does radiant energy differ from food resources of a green plant?

5.How is solar radiation fixed by green plants?

6.What amount of solar radiation is available as a resource for green plants?

Reading C: O2 as a resource

Ex.1. Read the following article and render it in Russian using a dictionary ( in a written form).

Notes to the article:

Waterlogged [‘wɔ:təlɔɡd] soil - заболоченная почва

Prokaryote - цианобактерия, простейший доядерный организм.

Eelworm - нематода

Autotrophic [ɔ:təu’trɔfiK] organisms – автотрофный организм

Heterotrophs [‘hetərəu’trɔfiK] – гетеротрофный организм

Decomposer – редуцент, деструктор (организм, разлагающий органические вещества)

Grazer – пасущееся животное

Fungi [‘fʌŋɡai] - грибы

Generalists (polyphagous – полифаг, многоядный организм, живущий на нескольких хозяевах)

Water fleaблоха

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Protein – белок

Carbohydrate - углевод

Pitcher-plant - саррацения

O2 is a resource for both animals and plants. Only a few prokaryotes can do without it. Its diffusibility and solubility in water are very low and so it becomes limiting most quickly in aquatic and waterlogged environments. Its solubility in water decreases rapidly with increasing temperature. When organic matter decomposes in an aquatic environment, microbial respiration makes a demand for O2 and this 'biological O2 demand' may constrain the types of higher animal that can persist. High biological O2 demands are particularly characteristic of still waters into which leaf litter or organic pollutants are deposited, and becomes most acute during periods of high temperature.

Because O2 diffuses so slowly in water, aquatic animals must either maintain a continual flow of water over their respiratory surfaces, or have very large surface areas relative to body volume or continually return to the surface to breath.

The roots of many higher plants fail to grow into waterlogged soil, or die if the water table rises after they have penetrated deeply. These reactions may be direct responses to O2 deficiency or responses to the accumulation of gases such as hydrogen sulphide, methane and ethylene, which are produced by microorganisms engaged in anaerobic decomposition. Even if roots do not die when starved of O2, they may cease to absorb mineral nutrients so that the plants suffer from mineral deficiency.

Reading D: Organisms as food resources

Ex.1. Read the following article and pay attention to three pathways consumers follow in ecological food chain.

Autotrophic organisms (green plants and certain bacteria) assimilate inorganic resources into 'packages' of organic molecules (proteins, carbohydrates, etc.). These become the resources for heterotrophs (decomposers, parasites, predators and grazers—organisms that require resources in organic, energy-rich form), and take part in a chain of events in which each consumer of a resource becomes, in turn, a resource for another consumer. At each link in this food chain we can usually recognize three pathways to the next body of consumers.

1 Decomposition, in which the bodies (or parts of bodies) of organisms die, and together with waste and secretory products, become a food resource for 'decomposers’

(bacteria, fungi and detritivorous animals)- a group which can use other organisms as food but only after they have died.

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2 Parasitism, in which the living organism is used as a food resource whilst it is still alive. We define a parasite as a consumer that usually does not kill its food organism and feeds from only one or a very few host organisms in its lifetime.

3 Predation, the final category, applies to those cases in which the consumer kills and eats another organism (or part of it) as food. Examples of predator-prey interactions are a water flea consuming phytoplankton cells, an acorn eaten by a beetle or squirrel, a mountain lion consuming a rabbit, a whale eating krill and perhaps even a pitcher-plant drowning a mosquito. Grazing can be regarded as a type of predation, but the food (prey) organism is not killed; only part of the prey is taken, leaving the remainder with the potential to regenerate. Grazers, in contrast to parasites but like most other predators, are likely to feed on (or from) many prey during their lifetime.

Two more categories deserve mention here: (i) the degree to which a consumer's diet is specialized or generalized in nature; and (ii) the relationship between the life spans of the consumer and its resource. Consumers may be generalists (polyphagous), taking a wide variety of prey species, although often with a rank order of acceptability amongst the foods that they take. Alternatively, a consumer may specialize on specific parts of its prey but range over a number of species. This is most common amongst herbivores because, as we shall see, different parts of plants are quite different in their composition. Thus, a variety of birds specialize on seeds, although they are seldom restricted to a particular species; many grazing animals specialize on leaves and do not usually take roots; and certain species of eelworm (nematodes) and the larvae of some beetle species are specialized root feeders. Amongst consumers of animals, parasites often attack particular tissues or organs but are not necessarily restricted to a single host species- Finally, a consumer may specialize on a single species or a narrow range of closely related species (when it is said to be monophagous). The more specialized the food resource required by an organism, the more it is constrained to live in patches of that resource or to spend time and energy in searching for it amongst a mixture. Such specialization may be fixed by peculiar structures, particularly mouthparts, which make it possible to deal efficiently with some resources, but of course make it more difficult to deal with others. Many food resources are seasonal, and this is illustrated by reference to a population of wild raspberries in a temperate woodland. In winter, the plant is a mass of tiny twigs, but in spring it develops an abundance of, young, protein-rich buds and juvenile leaves. Flowering brings a short period of nectar production offering a quite new type of resource, but only for the flowering period. As fruit is set, a new flush of resources is displayed in ripening and ripe fruit. Such seasonal structures may be reliable resources either to generalist herbivores that can turn to other foods when raspberry is out of season or to specialists that have an active life concentrated in the appropriate season and spend the rest of the year making no demands on food. The bird species feeding on raspberry fruits are generalists, taking them only as a seasonal component of a diet that varies continuously throughout the year. In complete contrast, the raspberry beetle is a raspberry specialist. It lays eggs in the flower and the larva completes its life cycle within the developing fruit. It then remains in

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diapause as a pupa until the raspberry flowers again 10-11 months later. The larva of the raspberry moth has a longer life on the pith within the woody stems: this resource is present throughout the year. This example illustrates both how a single resource (the raspberry plant) can be used by a variety of types of consumer and also, that a single species of plant can be many different resources.

Ex.2. Read the article once again and find the answers to the following questions:

1.What is food chain?

2.What are three main categories of predator-prey interactions?

3.How do grazers differ from parasites?

4.How selective are consumers towards their diet?

5.What is the relationship between the life spans of the consumer and its resource?

6.How can a single resource be used by a variety of types of consumer and how can a single species represent many different resources?

Ex.3. Find English equivalents of the following words and expressions in the text:

Автотрофные организмы ассимилируют неорганические ресурсы в органические вещества; цепь событий; отходы и секреторные продукты; пищевой ресурс; взаимодействия: хищник – жертва; продолжительность жизни; разнообразие видов-жертв; специализироваться на семенах; ограничиваться определенным видом; травоядные животные; корнееды; вид-хозяин; тесно взаимосвязанные виды; необходимый организму; ротовые части; эффективно справляться с некоторыми видами ресурса; сезонный; молодые листья; период цветения; когда плод завязывается; зрелый плод; надежный ресурс; могут перейти на другую пищу; проводят остальную часть года, не испытывая потребности в пище; жизненный цикл.

Ex.4. Render the following sentences in English:

1.Гетеротрофным организмам необходимы ресурсы в органической, богатой энергией форме.

2.В экологической пищевой цепи каждый консумент ресурса становится, в свою очередь, ресурсом для другого консумента.

3.Существуют три основные направления движения пищевого ресурса к следующему организму-потребителю на каждом звене пищевой цепи.

4.Деструкция – это когда тела организмов умирают и вместе с секреторными продуктами и другими отходами становятся пищевым ресурсом для редуцентов.

5.Паразитизм – это когда в качестве пищевого ресурса используется живой организм; консумент за время своей жизни обычно кормится от одного или нескольких организмов-хозяев.

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6.Хищничество относится к тем случаям, когда консумент убивает и поедает другой организм в качестве пищи.

7.Консументы могут быть полифагами, т.е. многоядными организмами. Они могут специализироваться на определенных частях жертвы, но не ограничиваться определенным видом.

8.Многие пищевые ресурсы могут быть только сезонными. Например, растение дикой малины зимой представляет массу тонких веток, но весной на них появляется изобилие молодых, богатых белком почек и листьев. Цветение приносит период появления нектара, и новый приток ресурса проявляется в созревающем плоде.

Unit 7

Grammar:

Infinitive. Infinitive constructions.

Ex.1. Translate the following sentences, pay attention to different functions of the Infinitive in them:

1.The life history is likely to be influenced by many factors.

2.There is often no programmed senescence of the whole modular organism – they appear to have perpetual somatic youth.

3.The polluted area is likely to support a much higher density of individuals.

4.Modular genetic analysis might be expected to give clean answers to such questions.

5.The niches of species that occur together in any one habitat are likely to be different.

6.Disappearance or decline on even a local scale is certain to excite conservationist interest.

7.No qualifications are required in order to argue in favour of sustainability.

8.Under a particular set of environmental conditions a predictable association of species is likely to occur.

9.Another alternative is to describe communities in terms of their standing crop and the rate of production of biomass by plants and its use and conversion by heterothrophic microorganisms and animals.

10.Organic insecticides were cheap, effective in small quantities and seemed to be truly ‘miracle insecticides’.

12.Augmentation involves the release of an indigenous natural enemy in order to supplement an existing population and is also therefore carried out repeatedly, typically so as to intercept a period of particularly rapid pest-population growth.

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13. There is a problem of subjecting the pest to an unrelenting selection pressure to which it is most likely to respond.

Word Study

Ex.1. Read the words. Give their Russian equivalents:

Fundamental, interest, colonization, demographic, individual, embryonic, phase, construction, accumulate, stage, reproduction, module, typical, proportion, role, unitary, mosquito, typify, dominate, concentrate, vertical, substrate, system, product, original, morphological, rosette [‘rouzet], characteristic, object, horizontal, integrated, variation, somatic, stolon, planula [plənju:lə]

Ex.2. Translate the following words and word combinations:

Unalterable ecological fact of life; insect pest; protected site; to favour birth; to hasten death; polluted stream; a wide range of species; recognizable nose; limbs with digits; accidents apart; infant; the only changes; a phase of senescence; can intervene at any time; the succession of phases is entirely predictable; on the other hand; a unit of construction (module); the most obvious group of modular organisms; models that are specialized for reproduction; physiologically separated parts; trunk of the tree; to repeat a characteristic pattern of shoots; to attach itself to a solid object; branched stalks; interconnecting network; to depauperate [di:’pɔ:pereit]; counterpart; perpetual somatic youth; succumb to [sə’Kʌm]; calcified branches;

Ex.3. Words to be remembered:

Distribution; abundance; unitary organisms; to exhibit; modular organism; to compare; predictable; to be composed of; juvenile phase; similar modules; higher plant; give rise to; specialized for; to cease; be determined by; misleading; seaweed; to concentrate on; vertical growth; root system; to rot away;

Reading A: An ecological fact of life

Notes to the text: Mercury - ртуть Locusts - саранча Zygote [zaiɡəut] - зигота

Uterus [‘ju:tərəs] - матка Foetus [‘fi:təs] - плод

Protista [prɔu’tistə] - протисты, простейшие одноклеточные организмы

Fungi [‘fʌŋɡai] - от fungus – грибы

Axillary [æK’siləri] – пазушный, axil – пазуха листа

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Internode of the stem - стеблевое междоузлие

Duckweed - ряска

Water lettuce - пистия

Rhizomatous - корневищный

Stoloniferous – дающий столоны

Perenniality [pə’rənjəliti] – постоянство

Ex.1. Read the following article and try to explain what ecological fact of life is.

There is a fundamental and unalterable ecological fact of life: Nnow=Nthen+B-D+I - E

In other words, the number of a particular organism presently occupying a particular site of interest (Nnow) is equal to the number previously there (Nthen), plus the number of births between then and now (B), minus the number of deaths (D), plus the number of immigrants (I), minus the number of emigrants (E). These facts of life define the main aim of ecology as to describe, explain and understand the distribution and abundance of organisms. Ecologists studying the effects of an insect pest on a crop will probably be trying to find ways of increasing Nfuture for the crop by

reducing Nfuturel for the pest; and those studying the distribution of a rare plant in a protected site will monitor the variation in Nnow from place to place and will

probably try to find out whether particular microsites favour colonization and birth, or hasten death. Ecologists studying the animal and plant community of a polluted stream will probably catalogue Nnow for a wide range of species, and compare these with data from similar but unpolluted streams. Even a study of the effects of temperature, light or a pollutant, such as mercury, on a particular organism has only ecological relevance insofar as the factor affects the birth, death or migration of the organism. In all cases, ecologists are interested in the number of individuals, the distributions of individuals, the demographic processes (birth, death and migration) which influence these and the ways in which these demographic processes are themselves influenced by environmental factors.

Unitary and modular organisms

In unitary organisms, form is highly determinate. Barring aberrations, all dogs have four legs, all locusts have six legs, all fish have one mouth and all squid have two eyes. Humans are perfect examples of unitary organisms. A life begins when a sperm fertilizes an egg to form a zygote. This implants in the wall of the uterus, and the complex processes of embryonic development commence. By 6 weeks the foetus has a recognizable nose, eyes, ears and limbs with digits, and accidents apart, it will remain in this form until it dies. The foetus continues to grow until birth, and then the infant grows until perhaps the 18th year of life; but the only changes in form (as opposed to size) are the relatively minor ones associated with sexual maturity. The reproductive phase lasts for perhaps 30 years in females and rather longer in males.

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This is followed by, or may merge into, a phase of senescence. Death can intervene at any time, but for surviving individuals the succession of phases is, like form, entirely predictable. In modular organisms, or the other hand, neither timing nor form is predictable. The zygote develops into a unit of construction (a module, e.g. a leaf with its attendant length of stem), which then produces further, similar modules. Individuals are composed of a highly variable number of such modules, and their programme of development is strongly dependent on their interaction with their environment. The product is almost always branched, and except for a juvenile phase, effectively immobile. Most plants are modular and are certainly the most obvious group of modular organisms. There are, however, many important groups of modular animals and many modular protista and fungi.

In the growth of a higher plant, the fundamental module of construction above ground is the leaf with its axillary bud and the attendant internode of the stem. As the, bud develops and grows, it produces further leaves, each bearing buds in their axils. The plant grows by accumulating these modules. At some stage in the development, a new sort of module appears, associated with reproduction (e.g. the flowers in a higher plant), ultimately giving rise to new zygotes. Modules that are specialized for reproduction usually cease to give rise to new modules (although this is not true of all modular animals). The roots of a plant are also modular, although the modules are quite different. The programme of development in modular organisms is typically determined by the proportion of modules that are allocated to different roles (e.g. to reproduction or to continued growth).

Many ecological and evolutionary generalizations have been made in the past as if the unitary animal (such as a human or a mosquito) in some way typifies the living world. This is highly misleading. Modular organisms such as seaweeds, corals, forest trees and grasses dominate large parts of the terrestrial and aquatic environments.

Modular organisms may broadly be divided into those that concentrate on vertical growth, and those that spread their modules laterally, over or in a substrate. Many plants produce new root systems associated with a laterally extending stem: these are the rhizomatous and stoloniferous plants. The connections between the parts of such plants may die and rot away, so that the product of the original organism becomes represented by physiologically separated parts. The most extreme examples of plants 'falling to pieces' as they grow are the many species of floating aquatics like duckweeds (Lemna), and the water lettuce (Pistia). Whole ponds, lakes or rivers may be filled with the separate and independent parts produced by a single zygote.

Trees are the supreme example of plants whose growth is concentrated vertically. The peculiar feature distinguishing trees and shrubs from most herbs is the connecting system linking modules together and connecting them to the root system. This does not rot away, but thickens with wood, conferring perenniality. Most of the structure of such a woody tree is dead, with a thin layer of living material lying immediately below the bark. The living layer, however, continually regenerates new tissue, and adds further layers of dead material to the trunk of the tree. The majority of a tree is a ‘cemetery’ in which dead stem tissues of the past are interred, but the strength of the trunk solves the difficult morphological problem of obtaining water

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and nutrients below the ground, but also light perhaps 50 m away at the top of the canopy.

We can often recognize two or more levels of modular construction. The fundamental units of higher plants are assembled into clusters with a form that is itself continually repeated. The strawberry is a good example of this: leaves are repeatedly developed from a bud, but these leaves are arranged into rosettes. 'The strawberry plant grows: (i) by adding new leaves to a rosette, and (ii) by producing new rosettes on stolons grown from the axils of its rosette leaves. Trees also exhibit modularity at several levels: the leaf with its axillary bud, the whole shoot on which the leaves are arranged and the whole branch systems that repeat a characteristic pattern of shoots.

The growth of modular animals can be illustrated by a hydrozoan, like Obelia. Development begins when a short-lived, free-swimming planula larva attaches itself to a solid object. It gives rise to a horizontal root-like structure that bears a number of branched stalks. The basic Obelia modules, the polyps [‘pɔlip] (which are both feeding and defensive structures), are borne on these stalks. The terminal polyp of each branch is temporarily the youngest, but is overgrown by the next one to develop, which arises as a bud at its base. The branched stalks remain as an interconnecting network between all the polyps in a colony. Reproduction in Obelia begins when tiny, free-swimming jellyfish are budded off from modified polyps called gonophores; these jellyfish then reproduce sexually to produce the dispersing planula larvae. Thus, these and similar animals, despite variations in their precise method of growth and reproduction, are as 'modular' as any plant. Moreover, in corals, for example, just like many plants, the individual may exist as a physiologically integrated whole, or may be split into a number of colonies—all part of one individual, but physiologically independent. The potentialities for individual difference are far greater in modular than in unitary organisms. For example, an individual of the annual plant Chenopodium album, may, if grown in poor or crowded conditions, flower and set seed when only 50 mm high. Yet, given more ideal conditions, it may reach 1 m in height, and produce 50 000 times as many seeds as its depauperate [di:’pɔ:pəreit] counterpart. It is modularity and the differing birth and death rates of plant parts, which give rise to this plasticity.

In fact, there is often no programmed senescence of the whole modular organism—they appear to have perpetual somatic youth. Even in trees that accumulate their dead stem tissues, or corals that accumulate old calcified branches, death often results from becoming too big or succumbing to disease rather than from programmed senescence.

Ex.2. Comprehension check-up:

1.What are fundamental ecological facts of life?

2.What is the main aim of ecology?

3.In what case is it important for an ecologist to study the demographic processes (birth, death and migration) of individuals?

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4.What is of great importance in unitary organisms?

5.Does the form of unitary organisms change greatly while they continue to grow? Is life form a predictable phase at each succession stage?

6.How do modular organisms differ from unitary ones?

7.What does their programme of development depend on?

8.In what way does a higher plant develop?

9.What is the programme of development in modular organisms typically determined by?

10.Which organisms: modular or unitary ones dominate environments?

11.How can modular organisms be divided?

12.What are rhizomatous plants?

13.Can you give examples of plants ‘falling to pieces” as they grow?

14.What peculiar feature distinguishes trees from most herbs?

15.How do trees develop?

16.What levels of modular construction is it possible to distinguish?

17.What is the typical process of growth for a modular animal?

18.Is individuality exhibited greater in modular organisms or in unitary ones?

19.Is it possible to say that a modular organism has a programmed senescence?

Ex.3. Translate the following words and word combinations into English:

Неоспоримый экологический факт, насекомое-вредитель, охраняемый участок, благоприятствовать рождаемости, приближать смерть, загрязненный ручей, различаемый нос, конечности с пальцами, не считая случайности, младенец, единственные изменения, фаза старения может наступить в любое время, смена жизненных фаз полностью предсказуема, с другой стороны, единица целого (модуль), наиболее показательная группа модулярных организмов, модули, которые отвечают за репродукцию, физиологически различные части, повторять характерную форму веточек, форма – определяющий фактор, прикрепиться к твердому объекту, стебли с ветвями, умереть от, отвердевшие ветки.

Reading B: Life cycles and the quantification of death and birth

Ex.1. Read the following article and answer the question: Why do scientists need to construct life tables, survivorship curves and fecundity schedules?

Ex.2. Translate the first 2 paragraphs into Russian (in written form).

Life cycles and the quantification of death and birth

To a large extent, patterns	of birth, death and growth are a reflection of the
organism's life cycle, of which	there are five main types (although there are many

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life cycles that defy this simple classification). The species are said to be either semelparous or iteroparous (often referred to by plant scientists as monocarpic and polycarpic). Like so many dichotomies in ecology, this one is not clear-cut: some species occupy the continuum between the two extremes. Nonetheless, we may say that in semelparous species, individuals have only a single, distinct period of reproductive output in their lives, prior to which they have largely ceased to grow, during which they invest little or nothing in survival to future reproductive events and after which they therefore die. In iteroparous species, on the other hand, an individual normally experiences several or many such reproductive events, which may in fact merge into a single extended period of reproductive activity. During each period of reproductive activity the individual continues to invest in future survival and possibly growth, and it therefore has a reasonable chance of surviving to reproduce again.

Often, in order to monitor and examine changing patterns of mortality with age or stage, a life table is used. Frequently this allows a survivorship curve to be constructed, which traces the decline in numbers, over time, of a group of newly born or newly emerged individuals – or it can be thought of as a plot of the probability, for a representative newly born individual, of surviving to various ages. Patterns of birth amongst individuals of different ages are often monitored at the same time as life tables are constructed. These patterns are displayed n fecundity schedules.

Life tables, survivorship curves and fecundity schedules are of the utmost importance because they contain the raw material of our 'ecological fact of life'. Without them we have little hope of understanding the Nnow of the species that interest us, and still less hope of predicting the Nfuture. Annual life cycles take approximately 12 months or rather less to complete. Usually, every individual in a population breeds during one particular season of the year, but then dies before the same season in the next year. Generations are therefore said to be discrete, in that each generation is distinguish-able from every other; the only overlap of generations is between breeding adults and their offspring during and immediately after the breeding season. Species with discrete generations need not be annual, since generation lengths other than 1 year are conceivable. In practice, however, most are: the regular annual cycle of climates provides the major pressure in favour of synchrony.

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PART II

Dispersal, Dispersion and Migration in Space and Time

1. Introduction

All organisms in nature are where we find them because they have moved there' This is true for even the most apparently sedentary of organisms, such as oysters and redwood trees. Their movements range from the passive transport that affects many plant seeds to the active movement of many mobile animals and their larvae.' The effects of such movements are also varied. In some cases, they aggregate members of a population into clumps; in others they continually redistribute and shuffle them amongst each other and in others they spread the individuals out and 'dilute' their density.

The terms dispersal and migration are used to describe certain aspects of the movement of organisms. Dispersal is most often taken to mean a spreading of individuals away from others (e.g. their parents or siblings), and it may involve active (walking, swimming, flying) or passive movements (carriage in water or wind)' Dispersal is therefore an appropriate description for several kinds of movements: (i) of plant seeds or starfish larvae away from each other and their parents; (ii) of voles from one area of grassland to another, usually leaving residents behind and being counterbalanced by the dispersal of other voles in the other direction; and (iii) of land birds amongst an archipelago of islands (or aphids amongst a mixed stand of plants) in the search for a suitable habitat..

Migration is most often taken to mean the mass directional movements of large numbers of a species from one location to another. The term therefore applies to classic migrations (the movements of locust swarms, the intercontinental journeys of birds, the transoceanic movements of eels), but also to less obvious examples tike the to-and-fro movements of shore animals following the tidal cycle. The terms dispersal and migration are both defined for groups of organisms' However, it is the individual that actually moves. Migration is mass movement' and an individual can only disperse, literally, if it separates into pieces. Many dispersing organisms (especially plant seeds and many marine larvae) have little or no control over where or how far they travel. They are simply hazarded into the world at large to be carried at the mercy of winds and waves. At the level of the individual, there is no sharp distinction between migration and dispersal.

2. Patterns of distribution: dispersion

The movements of organisms affect the spatial pattern of their distribution (their dispersion) and we can recognize three main patterns of dispersion, although they form part of a continuum.

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Random when there is an equal probability of an organism occupying any point in space (irrespective of the position of any others)' The result is that individuals are unevenly distributed because of chance events.

Regular dispersion (also called, uniform, even or overdispersion) occurs either when an individual has a tendency to avoid all other individuals, or when individuals that are especially close to others die. The result is that individuals are more evenly spaced than expected from chance.

Aggregated dispersion (also called contagious, clumped or underdispersion) occurs either when individuals tend to be attracted to (or are more likely to survive in) particular parts of the environment, or when the presence of one individual attracts' or gives rise to, another close to it. The result is that individuals are closer together than expected from chance.'

These patterns are defined by the relative positions of the organisms to one another, but how they will appear to an observer or be relevant to the life of another organism depends on how the spatial scale is sampled. For example, consider the distribution of an aphid living on a particular species of tree in a woodland. If the area is sampled with large samples, for example acre or hectare quadrats, the aphids will appear to be aggregated in particular parts of the world, i.e. in woodlands, as opposed to other types of habitat. If our samples are smaller and taken only in woodlands, the aphids will still appear to be aggregated, but now on their host tree species rather than on the trees in general. However, if our samples were still smaller (25 cm2, about the size of a leaf) and were taken within the canopy of a single tree, the aphids might appear to be randomly distributed over the tree as a whole. An even smaller quadrat (1 cm2) might detect a regular distribution because individual aphids on a leaf avoid one another.

In practice, the populations of all species are patchily distributed at some scale or another. One of the most important consequences of the patchy distribution of organisms is that we can have quite misleading measures of their effective density. For example, the human density of a country or region is usually calculated as the total number of individuals divided by the total land area. For the contiguous 48 states of the USA, the 196O census would give the population density as 59.94 persons per square mile. But, because most people live in patches, (towns and cities), their effective density is really about 3000 persons per square mile. When we come to consider the role of density in regulating natural populations it becomes vitally important to distinguish average density from effective density: a population may have a very low average density, but the few individuals may be very close together.

It is immensely more difficult, but ecologically even more relevant, to describe the dispersion of organisms on scales that are relevant to the life style of motile organisms. MacArthur and Levins introduced the concept of environmental grain to make this point. For example, the canopy of an oak hickory forest is fine grained (not patchy), from the point of view of a bird like the scarlet tanager which forages indiscriminately in both oaks and hickories, but is coarse grained (patchy) for defoliating insects which attack either oaks or hickories preferentially. Indeed it has been argued that ‘the problem of pattern and scale is the central problem in ecology,

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unifying population biology and ecosystem science, and marrying basic and applied ecology’ (Levin,1992).

3Dispersal

3.1Dispersal as escape and discovery

Dispersal is the term applied to the process by which individuals escape from the immediate environment of their parents and neighbours, and become less aggregated; dispersal may therefore relieve local congestion. But, dispersal can also often involve a large element of discovery. A useful distinction can be made between two types of such 'discovery dispersal'. First, there is dispersal in which individuals visit and 'explore' a large number of sites before returning and settling in a chosen one. Second, there is dispersal in which individuals visit a succession of locations, but then cease to move (with no element of 'return' to a site previously explored). In fact, this latter category can be split further into cases where the cessation of movement is under the dispersing organism's control, and cases where it is not.

The dispersal of plant seeds is non-exploratory and beyond the control of the seed itself. The discovery aspect of seed dispersal is therefore a matter of chance (although the chances of reaching a suitable site may be increased by the specializations for dispersal that the seeds possess). Animal dispersal, on the other hand, can fall into any of the three categories. Some animals have essentially the same type of dispersal as plant seeds. Many other animals cannot be said to explore, but they certainly control their settlement, and cease movement only when an acceptable site has been found. For example, most aphids, even in their winged form, have powers of flight which are too weak to counteract the forces of prevailing winds. But, they control their take-off from their site of origin, they control when they drop out of the windstream and they make additional, often small-scale flights if their original site of settlement is unsatisfactory. Their dispersal, therefore, involves ‘discovery’, over which they have some, albeit limited, control.

All species disperse, but some are more dispersive than others. Insects living in habitats tat are, by nature, temporary have a more pronounced dispersive phase than insects living in more permanent habitats. In general, dispersal is essential for the persistence of species that exploit temporary stages in a changing community. The descendants of individuals of all successional species are doomed in their local habitats. Yet, even the species of so-called ‘climax’ communities (the relatively stable endpoints of successions) are doomed in the long run unless they colonize new areas.The movements of forests following the advance and retreat of ice-sheets, or of tropical forests following arid periods, are on a different time scale to that usually associated with the dispersal of organisms. However, they make the same point, that in the life of all terrestrial organisms home is sooner or later a dangerous place.

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3.2 Dormancy: dispersal in time

An organism gains in fitness by dispersing its progeny, as long as the progeny are more likely to leave descendants than if they remained undispersed. Similarly, an organism gains in fitness by delaying its arrival on the scene, so long as the delay increases its chances of leaving descendants. This will often be the case when conditions in the future are likely to be better than those in the present. Thus, a delay in the recruitment of an individual to a population may be regarded as migration in time' and as an alternative to migration in space, and there are trade-offs between the two types of dispersal. Organisms generally spend their period of delay in a state of dormancy. This relatively inactive state has the benefit of conserving energy, which can then be used during the period following the delay. In addition, the dormant phase of an organism is often more tolerant of the adverse environmental conditions prevailing during the delay (i'e' tolerant of drought, extremes of temperature, lack of light, and so on). Dormancy can be either predictive or consequential. Predictive dormancy is initiated in advance of the adverse conditions, and is most often found in predictable' seasonal environments. It is referred to as ,diapause, in animals' and in plants as 'innate' or 'primary' dormancy. Consequential (or ‘secondary’) dormancy, on the other hand, is initiated in response to the adverse conditions themselves.

Intraspecific Competition

1. Introduction: The nature and features of intraspecific competition

Organisms grow, reproduce, die and migrate. They are affected by the conditions in which they live and by the resources that they obtain. Yet, no organism lives in isolation. Each, for at least part of its life, is a member of a population composed of individuals of its own species.

Individuals of the same species have very similar requirements for survival, growth and reproduction; but their combined demand for a resource may exceed the immediate supply. The individuals then compete for the resource and, not surprisingly, at least some of them become deprived.

Consider, initially, a simple hypothetical community: a thriving population of grasshoppers (all of one species) feeding on a field of grass (also of one species). In order to provide themselves with energy and material for growth and reproduction, grasshoppers must eat grass; but, in order to find and consume that grass, they must use energy. Any grasshopper might find itself at a spot where there is no grass because some other grasshopper has eaten it. The grasshopper must then move on and expend more energy before it takes in food. The more grasshoppers there are competing for food, the more often this will happen. Yet, an increased energy expenditure and a decreased rate of food intake may all decrease a grasshopper's chances of survival, and also leave less energy available for development and reproduction. Survival and reproduction determine a grasshopper's contribution to the

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next generation. Hence, the more intraspecific competitors for food a grasshopper has, the less its likely contribution will be.

As far as the grass itself is concerned, an isolated seedling in fertile soil may have a very high chance of surviving to reproductive maturity. It will probably exhibit an extensive amount of modular growth, and will probably therefore eventually produce a large number of seeds. However, a seedling, which is closely surrounded by neighbours (shading it with their leaves and depleting the water and nutrients of its soil with their roots) will be very unlikely to survive, and if it does, will almost certainly form few modules and set few seeds.

We can see immediately that the ultimate effect of competition on an individual is a decreased contribution to the next generation compared with what would have happened had there been no competitors. Intraspecific competition typically leads to decreased rates of resource intake per individual, and thus to decreased rates of individual growth or development, or perhaps to decreases in amounts of stored reserves or to increased risks of predation. These may lead, in turn, to decreases in survivorship and/or decreases infecundity. In many cases, competing individuals do not interact with one another directly. Instead, individuals respond to the level of a resource, which has been depressed by the presence and activity of other individuals. Thus, grasshoppers competing for food are not directly affected by other grasshoppers, but by a reduction in food level and an increased difficulty in finding good food. Similarly, a competing grass plant is adversely affected by the presence of close neighbours because the zone from which it extracts resources (light, water, nutrients) has been overlapped by the 'resource depletion zones' of these neighbours, making it more difficult for the original plant to extract its resources. In all these cases, competition may be described as exploitation, in that each individual is affected by the amount of resource that remains after it has been exploited by others. Exploitation can only occur, therefore, if the resource in question is in limited supply. In many other cases, however, competition takes a form known as, interference. Here, individuals interact directly with each other, and one individual will actually prevent another from exploiting the resources within a portion of the habitat. For instance, this is seen amongst animals that defend territories and also amongst the sessiIe animals and plants that live on rocky shores and amongst terrestrial plants. For example, the presence of a barnacle on a rock prevents any other barnacle from occupying that same position, even though the supply of food at that position may exceed the requirements of several barnacles. In such cases, space can be seen as a resource in limited supply. Another type of interference competition occurs when, for instance, two red deer stags fight for access to a harem of hinds. In this case, the hinds arc a resource in limited supply, because although either stag, alone, could readily mate with all the hinds, they cannot both do so since matings are limited to the 'owner' of the harem.

Thus, interference competition may occur for a resource of real value (e.g. space on a rocky shore for a barnacle), in which case the interference is accompanied by a degree of exploitation, or for a surrogate resource (a territory, or ownership of a harem), which is only valuable because of the access it provides to a real resource

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(food within a territory, the right to mate with all females). Interference for a surrogate can replace, in a sense, exploitative competition for a real resource. Hence, whereas with exploitation the intensity of competition is closely linked to the level of resource present and the level required, with interference, intensity may be high even when the level of the real resource is not limiting.

In practice, many examples of competition probably include elements of both exploitation and interference. For instance, our hypothetical grass plant, apart from suffering from the resource depletion of its competitors, would be physically excluded by them from the sites they already occupy. To take a more specific example, adult cave beetles, Neapheanops tellkampfi, in Great Onyx Cave, Kentucky, compete amongst themselves but with no other species and have only one type of food—cricket eggs, which they obtain by digging holes in the sandy floor of the cave. On the one hand, they suffer indirectly from exploitation: beetles reduce the density of their resource (cricket eggs) and then have markedly lower fecundity when food availability is low. But, they also suffer directly from interference : at higher beetle densities they fight more, forage less, dig fewer and shallower holes and eat far fewer eggs than could be accounted for by food depletion alone.

Whether they compete through exploitation or interference, individuals within a species are in essence equivalent, having many fundamental features in common, using similar resources and reacting in much the same way to conditions. However, there are many occasions when intraspecific competition is very one sided: a strong, early seedling will shade a stunted, late one; and an older and larger bryozoan on the shore will grow over a smaller and younger one. The overwinter survival of red deer calves in the resource-limited population on the island of Rhum declined sharply as the population became more crowded, but those that were smallest when born were by far the most likely to die.

Intrinsic, heritable differences between individuals may also ensure that competitive interactions are not reciprocal. For instance, tall corn plants will usually shade; and suppress genetically distinct short plants of the same species.

This lack of exact equivalence means that the ultimate effect of competition is far from being the same on different individuals. Weak competitors may make only a small contribution to the next generation, or no contribution at all. Strong competitors may have their contribution only negligibly affected. Indeed, a strong competitor may actually make a larger proportional contribution when there is intense competition than when there is no competition at all (i.e. if they maintain their contribution whilst all around them are losing theirs). In other words, although the ultimate effect of competition is a decrease in reproductive output, this does not always mean a decrease in individual fitness (i.e. 'relative' contribution).

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Interspecific Competition

1. Introduction

The essence of interspecific competition is that individuals of one species suffer a reduction in fecundity, survivorship or growth as a result of resource exploitation or interference by individuals of another species. This competition is likely to affect the population dynamics of the competing species, and the dynamics, in their turn, can influence the species' distributions and their evolution. Of course, evolution, in its turn, can influence the species' distributions and dynamics.

2. Some examples of interspecific competition

Competition between salamanders

The first example concerns two species of terrestrial salamanders, Plethodon glutinosus apd P. jordani, which live in the southern Appalachian Mountains of the USA. Generally, P. jolani lives at higher altitudes than P. glutinosus, but in certain areas their altitudinal distributions overlap. Hairston (1980) carried out an experiment at two sites, one in the Great Smoky Mountains and the other in the Balsam Mountains. These sites both had populations of the two salamander species, they had similar salamander faunas overall, they were at the same elevation and they faced the same direction. At both sites, seven experimental plots were established in I974: two from which P. jordani was removed, two from which P. glutinosus was removed and three as controls. Then, six times in each of the next 5 years, the numbers of both species and their ages were estimated in all plots.

In the control plots, and naturally, P. jordani was by far the more abundant of the two species; and in the plots from which it was removed, there was a statistically significant increase in the abundance of P. glutinosus at both locations. In the plots from which P.glutinosus was removed, there was no significant reciprocal increase in the abundance of P. jordani. However, there was, at both sites, a statistically significant increase in the proportion of p. iordani in the 1- and 2-year-old age classes. This was presumably a result of increased fecundity and/or increased survival of young, both of which are crucial components of the basic reproductive rate.

The important point is that individuals of both species must' originally' have been adversely affected by individuals of the other species' since when one species was removed, the remaining species showed a significant increase in abundance and/or fecundity and/or survivorship. It appears, therefore, that in the control plots and in the other zones of overlap generally, these species competed with one another but still coexisted.

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Competition between bedstraws (Galium spp.)

A.G. Tansley, one of the greatest of the 'founding fathers' of plant ecology, studied competition between two species of bedstraw. Galium hercynicum is a species which grows in Great Britain at acidic sites, whilst G. pumilurn is confined to more calcareous soils (in Tansley's time they were known as G. saxatile and G. sylvestre). Tansley found that as long as he grew them alone, both species would thrive on both the acidic soil from a G. hercynicum site and the calcareous soil from a G. pumilum site. Yet, if the species were grown together, only G. hercynicum grew | successfully in the acidic soil and only G. pumilum grew successfully in the calcareous soil. It seems, therefore, that when they grow together the species compete, and that one species wins, whilst the other loses so badly that it is competitively excluded from the site. The outcome depends on the habitat in which the competition occurs.

Competition between barnacles|

The third study concerns two species of barnacle in Scotland: Chthamalus stellatus and Balanus balanoides. These species are frequently found together on the same Atlantic rocky shores of north-west Europe. However, adult Chthamalus generally occur in an intertidal zone which is higher up the shore than that of adult Balanus, even though young Chthamalus settle in considerable numbers in the Balanus zone. In an attempt to understand this zonation, Connell monitored the survival of young Chtharnalus in the Balanus zone. He took successive censuses of mapped individuals over the period of 1 year and, most important, he ensured at some sites that young Chthamlus that settled in the Balanus zone were kept free from contact with Balanus. In contrast with the normal pattern, such individuals survived well, irrespective of the intertidal level. Thus, it seemed that the usual cause of mortality in young Chthamalus was not the increased submergence , times of the lower zones, but competition from Balanus in those zones. Direct observation confirmed that Balanus smothered, undercut or crushed Chthamalus, and the greatest Chthamalus mortality occurred during the seasons of most rapid Balanus growth. Moreover, the few Chthamalus individuals that survived I year of Balanus crowding were much smaller than uncrowded ones, showing, since smaller barnacles produce fewer offspring, that interspecific competition was also reducing | fecundity.

Thus, Balanus and Chthamalus compete. They coexist on the same shore, but on a finer scale their distributions overlap very little. Balanus outcompetes and excludes Chtharnalus from the lower zones; but Chthamalus can survive in the upper zones where Balanus, because of its comparative sensitivity to desiccation, cannot.

Assessment: some general features of interspecific competition

Individuals of different species can compete. This is hardly surprising. It seems, moreover, that competing species may either exclude one another from particular habitats so that they do not coexist (as with the bedstraws, the diatoms and the first

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pair of Paramecium spp.), or may coexist (as with the salamanders), perhaps by utilizing the habitat in slightly different ways (e.g. the barnacles and the second pair of Paramecium spp.).

But what about the tit study? Certainly the five species coexisted and utilized the habitat in slightly different ways. But did this have anything to do with competition? Lack thought so. In Connell’s phrase, he invoked 'the ghost of competition past'. In other words, he believed that they coexisted as a result of evolutionary responses to interspecific competition. This requires some further explanation. When two species compete, individuals of one or both species may suffer reductions in fecundity and/or survivorship, as we have seen. The fittest individuals of each species may then be those that (relatively speaking) escape competition because they utilize the habitat in ways that differ most from those adopted by individuals of the other species. Natural selection will then favour such individuals, and eventually the population may consist entirely of them. The two species will evolve to become more different from one another than they were previously, they will compete less, and thus will be more likely to coexist.

The trouble with this as an explanation for the tit data is that there is no proof. We cannot go back ii time to check whether the species ever competed more than they do now, and it was not even part of the study to determine the extent o[ present-day competition. One plausible alternative interpretation, therefore, is that ' the species have, in the course of their evolution, responded to natural selection it different but entirely independent ways. They are distinct species, and they have distinctive features. But, they do not compete now, nor have they ever competed; they simply happen to be different. If all this were true, it might seem that the coexistence of the tits has nothing to do with competition. On the other hand, it may be that competition in the past eliminated a number of other species, leaving behind, only those that were different in their utilization of the habitat. In other words, we can still see the hand of the ghost of competition past, but it acted as an ecological force (eliminating species), rather than an evolutionary one (changing them).

The tit study therefore, and the difficulties with it, illustrate two important general points. The first is that we must pay careful, and separate, attention to both the ecological and the evolutionary effects of interspecific competition. The ecological effects, as we have seen, are, broadly, that species may be eliminated from a habitat by competition from individuals of other species, or, if competing species coexist, that individuals of at least one of them suffer reductions in survival and/or fecundity. The evolutionary effects appear to be that species differ more from one another than they would otherwise do, and hence compete less.

The second point, however, is that there are profound difficulties in invoking competition as an explanation for observed patterns, and especially in invoking it as an evolutionary explanation. An experimental manipulation (for instance, the removal of one or more species) can, as we have seen with the salamanders and barnacles, indicate the presence of current competition, if, say, it leads to an increase, in the fecundity or survival or abundance of the remaining species. but negative: results would be equally compatible with the past elimination of species by competition, the

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evolutionary avoidance of competition in the past, and independent evolution of noncompeting species. In fact, for many sets of data, there are no easy or agreed methods of distinguishing between these explanations.

For now, though, what other general features emerge from our examples? As with intraspecific competition, a basic distinction can be made between interference and exploitation competition (although elements of both may be found in a single interaction). With exploitation, individuals interact with each other indirectly, responding to a resource level that has been depressed by the activity of competitors. The diatom work provides a clear example of this. By contrast, Connell's barnacles provide an equally clear example of interference competition. Balanus, in particular, directly and physically interfered with the occupation by Chthamalus of limited space on the rocky substratum.

Interference, on the other hand, is not always as direct as this. Amongst plants, it has often been claimed that interference occurs through the production of chemicals that are toxic to other species but not to the producer (known as allelopathy). There is no doubt that chemicals with such properties can be extracted from plants, but their role is controversial. Allelopathy has been proposed with enthusiasm, welcomed and supported with enthusiasm, dismissed with great skepticism, treated as an established, uncontroversial fact and suggested soberly as a subject for serious enquiry. Amongst competing tadpole species, too, water-borne inhibitory products have been implicated as a means of interference (most notably, perhaps, an alga produced in the faeces of the common frog, Rana temporaria, inhibiting the natterjack toad, Bufo calamita, but here again their importance in nature is unclear. Of course, the production by fungi, actinomycetes and bacteria— especially those found in the soil—of chemicals that inhibit the growth of potentially competing microorganisms is widely recognized—and exploited in the selection and production of antibiotics.

Interspecific competition (like intraspecific competition) is frequently highly asymmetric—the consequences are often not the same for both species. For instance, with Connell's barnacles, Balanus excluded Chthamalus from their zone of potential overlap, but any effect of Chthamalus on Balanus was negligible: Balanus was limited by its own sensitivity to desiccation. A closely analogous situation is provided by two species of cattail (reedmace) in ponds in Michigan, where one species, Typha latifolia, was rnostly found in shallower water, whilst the other, T.angustifolia, occurred in deeper water. Experimental manipulations suggested that amongst newly established plants, T.latifolia normally excludes T. angustifolia from shallower water. But the distribution of T.latifolia is unaffected by competition with T.angustifolia. On the other hand, in the longer term, after establishment is complete, the asymmetry is largely reversed: at all but the shallowest depths, T. angustifolia expands at the expense of T. latifolia and is apparently unaffected by its presence.

On a broader front, it seems that highly asymmetric cases of interspecific competition (where one species is little affected) outnumber symmetric cases by around two to one in insects in herbaceous plants and more generally, too. The more fundamental point, however, is that there is a continuum linking the perfectly symmetric

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competitive cases to the 'perfectly' asymmetric ones. For instance, showed this in a study of 'overgrowth competition' amongst bryozoan species (colonial, modular animals) living on the undersurfaces of corals off the coast of Jamaica. For the pairwise interactions amongst the seven most commonly interacting species, he found that the 'percentage wins' varied more or less continuously from 50% (perfect symmetry) to 100% (perfect asymmetry). Finally, it is worth noting that competition for one resource often affects the ability of an organism to exploit another resource. For example, Buss (1979), showed that in bryozoan overgrowth interactions, there appears to be an interdependence between competition for space and for food. When a colony of one species contacts a colony of another species, it interferes with the self-generated feeding currents on which bryozoans rely (competition for space affects feeding). But a colony short of food will, in turn, have a much reduced ability to compete for space (by overgrowth).

Comparable examples are found amongst rooted plants. lf one species invades the canopy of another and deprives it of light, the suppressed species will suffer directly from the reduction in light energy that it obtains, but this will also reduce its rate of root growth, and it will therefore be less able to exploit the supply of water and nutrients in the soil. This in turn will reduce its rate of shoot and leaf growth. Thus, when plant species compete, repercussions flow backwards and forwards between roots and shoots. A number of workers have attempted to separate the effects of canopy and root competition by an experimental design in which two species are grown: (i) alone; (ii) together; (iii) in the same soil, but with their canopies separated; and (iv) in separate soil with their canopies intermingling. One example is a study of subterranean clover and skeleton weed. The clover was not significantly affected under any circumstances (another example of asymmetric competition). However, the skeleton weed was affected when the roots intermingled (reduced to 65% of the control value of dry weight) and when the canopies intermingled (47% of the control). When both intermingled, the effect was multiplicative, dry weight being reduced to 31% of the control, compared with the 3O.6% (65 x 47%) that might have been expected.

THE NATURE OF PREDATION

1. Introduction: the types of predators

Consumers affect the distribution and abundance of the things they consume and vice versa, and these effects are of central importance in ecology. Yet, it is never an easy task to determine what the effects are, how they vary and why they vary. We begin here by asking 'What is the nature of predation?' and 'What are the effects of predation on the predators themselves and on their prey?' Predation, put simply, is consumption of one organism (the prey) by another organism (the predator), in which the prey is alive when the predator first attacks it. This excludes detritivory, the consumption of dead organic

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matter. Nevertheless, it is a definition that encompasses a wide variety of interactions and a wide variety of 'predators'.

There are two main ways in which predators can be classified. Neither is perfect, but both can be useful. These classifications will not be pursued with the aim of constructing a neat and tidy catalogue, or of settling any issues in semantics. However, by distinguishing various types of predator, and establishing what characteristics they share and how they differ, we will be able to develop a fuller understanding of the precise nature of predation. The most obvious classification, perhaps, is 'taxonomic': carnivores consume animals, herbivores consume plants and omnivores consume both. An alternative, however, is a 'functional' classification (Thompson, 1982). Here, there are four main types of predator: true predators, grazers, parasitoids and parasites, (the last divisible further into microparasites and macroparasites).

True predators kill their prey more or less immediately after attacking them; during their lifetime they kill several or many different prey individuals. Often, they consume prey in their entirety, but some true predators consume only parts of their prey. Most of the more obvious carnivores like tigers, eagles, coccinellid beetles and carnivorous plants are true predators, but so too are seed-eating rodents and ants, plankton-consuming whales, and so on.

Grazers also attack large numbers of prey, one after the other, during their lifetime, but they remove only a part of each prey individual rather than the whole. Their effect on a prey individual, although typically harmful, is rarely lethal in the short term, and certainly never predictably lethal ( in which case they would be true predators). Amongst the more obvious examples are the large vertebrate herbivorous like sheep and cattle, but the flies that bite vertebrates, and leeches that suck blood are also undoubtedly grazers by this definition.

Parasites, like grazers, consume parts of their prey (their ‘host’) rather than the whole. Also like grazers, their attacks are typically harmful but rarely lethal in the

short term. Unlike grazers, however, their attacks are concentrated on one or a very few individuals during the course of their life. There is, therefore, an intimacy of association between parasites and their hosts which is not seen in predators and grazers. Tapeworms, liver flukes, the measles virus, the tuberculosis bacterium and the flies and wasps that form mines and galls on plants are all obvious examples of parasites. There are also considerable numbers of plants, fungi and microorganisms that are parasitic on plants (often called ‘plant pathogens’), for instance, the rusts and smuts and the mistletoes. Moreover, there are also herbivores that may readily be thought of as parasites. For example aphids extract sap from one or a very few individual plants with which they enter into intimate contact. Even caterpillars often rely on a single plant for their development ( although the association here is not so intimate). Caterpillars may be grazers (where they take small parts of several plants) or even true predators (where they destroy several plants – perhaps young seedlings) – and many undoubtedly may be somewhere on a continuum between these categories.

The parasitoids are a group of insects that are classified as such as the basis of the egg-laying behavior of the adult female and the subsequent developmental pattern of the larva. They are free-living as adults, but they lay their eggs in, on or near other

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insects (or, more rarely, in spiders or woodlice). The larvae of parasitoid then develops inside its host individual, which is usually a pre-adult. Initially, it does little apparent harm to the host, but eventually it almost totally consumes the host and therefore kills it before or during the pupal stage. An adult parasitoid, rather than an adult host, emerges from what is apparently a host pupa. Often, just one parasitoid develops from each host, but in some cases several individuals share a host. Thus, parasitoids .are intimately associated with a single host individual (like parasites); they do not cause immediate death of the host (like parasites and grazers), but their eventual lethality is inevitable (like predators). For parasitoids, and also for the many herbivorous insects that feed as larvae on plants, the rate of 'predation' is determined very largely by the rate at which adult females oviposit. Each egg laid by the female is an 'attack' on the prey or host, even though it is the larva that develops from the egg that actually does the eating.

Parasitoids may seem to be an unusual group of limited general importance. However, it has been estimated that they account for 10% or more of the world's species (Godfray, 1994). This is not surprising when we consider that there are so many species of insects, that most of these are attacked by at least one parasitoid and that even parasitoids themselves may be attacked by parasitoids. Moreover, a number of parasitoid species have been intensively studied by ecologists, and they have provided a wealth of information relevant to predation generally.

The effects of herbivory on a plant depend on precisely which parts are affected, and on the timing of the attack relative to the plant's development. Leaf biting, sap sucking, mining, meristem consumption, flower and fruit damage and root pruning are all likely to differ in the effect they have on the plant. The consequences of defoliating a germinating seedling are unlikely to be the same as those of defoliating a plant that is setting its own seed. Moreover, because the plant usually remains alive in the short term, the effects of herbivory are crucially dependent on the response of the plant. Minerals or nutrients may be diverted from one part to another, the overall rate of metabolism may change, the relative rates of root growth, shoot growth and reproduction may alter and special protective chemicals or tissues may be produced. Overall, the effect of a herbivore may be more drastic than it appears, or less drastic. It is only rarely what it seems.

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2.THE BEHAVIOUR OF PREDATORS

2.1Introduction

In this article we discuss the behaviour of predators. We examine where they feed what they feed on, how they are affected by other predators and how they are affected by the density of their prey. These topics are of interest in their own right, but they are also relevant in two other, broader contexts. First, foraging is an аspect of animal behaviour that is subject to the scrutiny of evolutionary biologists, within the general field of 'behavioural ecology'. The aim, put simply, is to try to understand how natural selection has favoured particular patterns of behaviour in particular circumstances (how, behaviourally, organisms match their environment).

Second, the various aspects of predatory behaviour can be seen as components that combine to influence the population dynamics of both the predator itself and ITS prey. It will be useful at various points to suggest the ways in which individual behaviour may affect population dynamics. If predation is such that one or other of the population is subjected to density dependent increases in mortality (or decreases in birth rate), then this will tend to regulate the size of that population within certain limits, i.e. it will tend to stabilize the dynamics of the population. This in turn will tend to stabilize the population dynamics of the interaction as a whole (the populations will be persistent and show relatively little variation in abundance). Conversely, if there is 'inverse density dependence', such that mortality decreases (or birth rate increase) with increasing density, then this will tend to destabilize the dynamics of the interaction. Predatory behaviour can clearly have a significance beyond its effect on the individuals concerned.

2.2 The widths and compositions of diets

Consumers can be classified as either monophagous (feeding on a single ргеу-type), oligophagous (few prey-types) or polyphagous (many prey-types). Often, an equally useful distinction is between specialists (broadly, monophages and oligophages) and generalists (polyphages). Herbivores, parasitoids and true predators can all provide examples of monophagous, oligophagous and polyphagous species. But the distribution of diet widths differs amongst the various types of consumer. True ргеdators with specialized diets do exist; for instance the Everglades kite (Rostraharmis sociabilis) feeds almost entirely on snails of the genus Pomacea—but most true predators have relatively broad diets. Parasitoids, on the other hand, are typically specialized and may even be monophagous. Herbivores are well represented in all categories, but whilst grazing and 'predatory' herbivores typically have broad diets, 'parasitic' herbivores are very often highly specialized. For instance, Janzen (1980) examined 110 species of beetle that feed as larvae inside the seeds of dicotyledonous plants in Costa Rica ('parasitizing' them) and found that 83 attacked only one plant species, 14 attacked only two, nine attacked three, two attacked four, one attacked six and one attacked eight. This was in spite of there being 975 plant species present in the area.

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2.3 Food preferences

It must not be imagined that polyphagous and oligophagous species are indiscriminate in what they choose from their acceptable range. On the contrary, some degree of preference is almost always apparent. An animal is said to exhibit a preference for a particular type of food when the proportion of that type in the animal's diet is higher than its proportion in the animal's environment. To measure food preference in nature, therefore, it is necessary not only to examine the animal's diet (usually by the analysis of gut contents) but also to assess the 'availability' of different food types. Ideally, this should be done not through the eyes of the observer (i.e. not by simply sampling the environment), but through the eyes of the animal itself.

The exact quantification of preference is therefore fraught with difficulties—but it is generally much easier at least to establish that a preference does exist. For instance, the results of an accidental field experiment, in which deer broke into a tree plantation, provide a nice example. The plantation contained equal numbers of four species arranged at random: white pine, red pine, jack pine and white spruce. As theTable shows, the deer, with free access to all four species, exhibited a fairly consistent preference for jack pine, followed by white pine, with red pine being only lightly browsed and white spruce ignored.

A food preference can be expressed in two rather different contexts. There can be a preference for items that are the most valuable amongst those available, or for items that provide an integral part of a mixed and balanced diet. These will be referred to as ranked and balanced preferences, respectively.

A feeding preference: the percentages of various planted trees browsed by deer when they broke into a plantation in which the four species of tree were equally abundant and arranged at random. (After Hortrin, 1964.)

White pine	Red pine	Jack pine	White spruce
Winter 1956-1957	31	19	84	0
Winter 1958-19599	1	48	0
Winter 1960-1961	17	0	70	0

There are two important reasons why a mixed diet may be favoured. First, consumers may accept low-quality items simply because, having encountered them, they have more to gain by eating them (poor as they are) than by ignoring them and continuing to search. Second, consumers may benefit from a mixed diet because each food type contains a different undesirable toxic chemical. A mixed diet would then keep the concentrations of all of these chemicals within acceptable limits. It is certainly the case that toxins can play an important role in food preference. For instance, one study examined the winter food of a variety of Arctic animals: three species of ptarmigan, three grouse, capercaillie, two kinds of hare and the moose (Bryant & Kuropat, 1980). In each case, the conclusions were the same: animals ranked their foods on neither energy nor nutrient content. Instead, preference was strongly and negatively correlated with the concentrations of certain toxins. Overall, however, it would be quite wrong to

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give the impression that all preferences have been clearly linked with one explanation or another. For example, Thompson (1988) has reviewed the relationship between the oviposition preferences of phytophagous insects and the performance of their offspring on these foodplants in terms of growth,- survival and reproduction. A number of studies have shown a good association (i.e. females preferentially oviposit on plants where their offspring perform best), but in many others the association is poor. In such cases, there is generally no shortage of explanations for the apparently unsuitable behaviour, but these explanations are, as yet, often just untested hypotheses.

2.4 Switching

The preferences of many consumers are fixed, i.e. they are maintained irrespective of the relative availabilities of alternative food types. But many others switch their preference, such that food items are eaten disproportionately often when they are common and are disproportionately ignored when they are rare. One study shows the fixed preference exhibited by predatory shore snails when they were presented with two species of mussel prey at a range of proportions. The assumption was made that they exhibited the same preference at all proportions. This assumption is clearly justified: irrespective of availability, the predatory snails showed the same marked preference for the thin-shelled, less protected Mytilus edulis, which they could exploit more effectively. By contrast, when guppies (a species of fish) were offered a choice between fruit-flies and tubificid worms as prey they clearly switched their preference, and consumed a disproportionate number of the more abundant prey-type.

There are a number of situations in which switching can arise. Probably the most common is where different types of prey are found in different microhabitats, and the consumers concentrate on the most profitable microhabitat.

Switching in a population often seems to be a consequence not of individual consumers gradually changing their preference, but of the proportion of specialists changing. This is illustrated by a study of switching in woodpigeons feeding on maple peas and tic beans. When the two were equally abundant there was a slight preference for maple peas; but when there were 82% tic beans on offer, the birds switched to an average of 91% tic beans in their diet. This average, however, included two birds that specialized on the rarer maple peas, taking only 5% and 0% tic beans.

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