The successive change of one community by another is called. Formation stages. Artificial ecosystems: agro and urban ecosystems

The addition of ecosystems is a dynamic process. In ecosystems, changes are constantly occurring in the state and life of their members and in the ratio of populations. The manifold changes occurring in any community are classified into two main types: cyclic and translational.

Cyclic changes   communities reflects the daily, seasonal and long-term periodicity of external conditions and the manifestation of internal (endogenous) rhythms of organisms.

Daily cycles are mainly associated with the rhythm of natural phenomena and is strictly periodic in nature. The seasonal variability of biocenoses is expressed in a change not only in state and activity, but also in the quantitative ratio of individual species depending on their breeding cycles, seasonal migrations, and the death of individual generations during the year.

The tier structure of the biocenosis is also often subject to seasonal variability: individual plant tiers can completely disappear in the corresponding seasons of the year, for example, a grassy tier consisting of annuals.

Long-term cyclicity depends on changes in meteorological conditions over the years (climatic fluctuations), uneven precipitation over the years, with periodic recurrence of droughts or other external factors affecting the community (for example, the degree of river spill). In addition, long-term periodicity may be associated with the life cycle features of edifier plants, with the repetition of mass reproduction of animals or microorganisms pathogenic for plants, etc.

Translational changesin the community ultimately lead to a change of this community to another, with a different set of dominant species. Such shifts may be caused by factors external to the cenosis that have been operating in the same direction for a long time, for example, the drainage of bog soils increasing as a result of land reclamation, increasing pollution of water bodies, increased grazing, etc. The resulting changes in one biocenosis are called another exogenetic. Endogenetic shifts   arise as a result of processes occurring within the community itself.

Successions

The successive change of one biocenosis by another is called (from lat. Succesio - sequence, change) - succession.Succession is a process of ecosystem self-development. The succession is based on the incompleteness of the biological cycle in this biocenosis. As a result of vital activity, every living organism changes its environment around itself, removing some of the substances from it and saturating it with metabolic products. With a more or less prolonged existence of populations, they change their environment in an unfavorable direction and as a result are crowded out by populations of other species for which the environmental transformations caused are environmentally beneficial. Thus, in the community there is a change in the dominant species. The successive series of gradually and naturally replacing each other in succession of communities is called succession series.

Distinguish between primary and secondary succession. Primary succession   It begins in lifeless places (on rocks, sand, cliffs). Secondary succession   - this is a sequential change of one community that existed on this substrate, another more perfect for these abiotic processes. Secondary successions occur, as a rule, faster and easier than the primary ones, since the soil profile, seeds, rudiments, and part of the former population and former ties are preserved in the disturbed habitat.

In any succession series, the pace of changes is gradually slowing down. The end result is the formation of a relatively stable stage - menopause community   or menopause. The initial, pioneer groupings of species are characterized by the greatest dynamism and instability. Menopausal ecosystems are capable of long-term self-maintenance in an appropriate range of conditions, since they acquire such features of the organization of biocenoses that allow maintaining a balanced circulation of substances.

7. Artificial ecosystems: agro and urban ecosystems

A person receives a lot of products from natural systems, however, agriculture is the main source of food for him.

Agroecosystems   created by man to obtain a high yield - the net products of autotrophs. Summarizing everything already said above about agroecosystems, we emphasize the following main differences from natural ones:

1. The diversity of species is sharply reduced in them: a decrease in the species of cultivated plants also reduces the species diversity of the animal population of the biocenosis; the species diversity of animals bred by humans is negligible compared to natural; Cultivated pastures (with grass sowing) are similar in type diversity to agricultural fields.

2. Species of plants and animals cultivated by humans “evolve” due to artificial selection and are uncompetitive in the fight against wild species without human support.

3. Agroecosystems receive additional energy subsidized by humans, except solar.

4. Net production (harvest) is removed from the ecosystem and does not enter the biocenosis food chain, and its partial use by pests, harvesting losses, which can also fall into natural trophic chains, are in every way suppressed by man.

Ecosystems of fields, orchards, pastures, kitchen gardens and other agrocenoses are simplified systems supported by humans in the early stages of succession, and they are just as unstable and incapable of self-regulation as natural pioneer communities, therefore they cannot exist without human support .

More than 50% of the world's population lives in cities today. Process urbanization   - This is the growth of the urban population, the number and size of cities, the increasing role of the city in people's lives, the spread of urban lifestyle. Today, urban areas occupy 1% of the land, but concentrate 50% of the world's population, produce 80% of the gross product (GDP), and give 80% of all emissions.

Metropolis- This is an overgrowth of cities. The interconnection of all components and phenomena of the urban and natural environment is called   urban ecosystem. Urboecosystems have a specific place in geographic space. These are open systems, managed. Their important feature is anthropocentrism.

Succession. Ecosystem Succession Examples

Succession

Types of Successions

Secondary succession

Types of Succession Changes

Succession duration

Ecosystem Succession Examples

Communities are constantly changing. Their species composition, the number of various organisms, trophic structure, and other indicators of the community are changing.

Community change over time.

Succession is a sequential, regular change of some communities by others in a certain part of the territory, due to internal factors of ecosystem development.

In order to understand the nature of ecological succession, imagine an IDEAL community (that is, the total production of autotrophs in energy terms exactly corresponds to the energy costs that go towards ensuring the vital functions of its constituent organisms).

In ecology, total energy costs are called - the general breath of the community.

It is clear that in such an ideal case, the processes of production are balanced by the processes of respiration.

Consequently, the biomass of organisms in such a system remains constant, and the system itself is unchanged or equilibrium.

If the "general respiration" is less than the primary gross output - an accumulation of organic matter will occur in the ecosystem;

If more - its decrease.

In both the first and second cases, community changes will occur.

With an excess of the resource, there will always be species — which can master it, and with a shortage — some of the species will die out.

Such a change is the essence of ecological succession

The main feature of this process is that community changes always occur in the direction of the equilibrium state.

1.1 Types of succession

Succession, which begins at a place deprived of life (for example, on a newly formed sand dune), is called primary succession.

In nature, primary successions are relatively rare and last much longer than secondary ones - up to several centuries.

Primary succession   - This is the overgrowing of a place not previously occupied by vegetation: bare rocks or frozen volcanic lava.

Example:

Community formation on a bare rock section, a section of frozen volcanic lava, on a newly formed sand dune or after the glacier leaves.

Only a few plants are able to live on such soil; they are called the pioneers of successions. Typical pioneers are mosses and lichens. They change the soil, releasing acid, which destroys and loosens stones. Dying mosses and lichens under the influence of bacteria - reducers decompose, and their remnants are mixed with loose stony substrate (sand).

This forms the first soil on which other plants can already grow. The need to destroy the parent rock is the main reason for the slow progress of primary successions; note the increase in soil thickness as succession occurs.

On soil that is poor in nutrients, grasses settle that are more specifically capable and crowd out lichens and mosses. Grass roots penetrate rock fissures, push these cracks apart and destroy the stone more and more.

Herbs are replaced by perennial plants and shrubs, such as alder and willow. Alder roots are nodules - special organs containing symbiotic bacteria that fix atmospheric nitrogen and contribute to the accumulation of large reserves in the soil, due to which the soil is becoming more fertile.

Now, trees, such as pine, birch and spruce, can already grow on it.

Thus, the driving force behind succession is that plants change the soil beneath them, affecting its physical properties and chemical composition, so that it becomes suitable for competing species that displace the original inhabitants, causing a change of community - succession, due to plant competition they do not always live where conditions are better for them.

The course of primary successions takes place in several stages.

For example, in the forest zone: dry lifeless substrate - lichens, mosses - annual forbs - grasses and perennial grasses - shrubs - trees of the 1st generation - trees of the 2nd generation; in the steppe zone, succession ends at the stage of grasses, etc.

1.2 Secondary succession

The term “secondary succession” refers to communities that develop in place of an already existing, previously formed community.

In places where the economic activities of people do not interfere with the relationships of organisms, a climax community develops that can exist indefinitely - until some external influence (plowing, forest cutting, fire, volcanic eruption, flood) violates its natural structure.

In the event of a community destruction, succession begins in it - a slow process of restoration of the initial state.

Examples of secondary successions:   overgrowing of an abandoned field, meadow, burning or logging.

Secondary succession lasts several decades.

It begins with the appearance of annual herbaceous plants on a cleared area of \u200b\u200bsoil. These are typical weeds: dandelion, sow thistle, coltsfoot and others. Their advantage is that they grow quickly and produce seeds adapted to spread over long distances with the help of wind or animals.

However, after two or three years, they are replaced by competitors - perennial grasses, and then - shrubs and trees, especially aspen.

These rocks obscure the ground, and their extensive root systems take all the moisture out of the soil, so that it becomes difficult for seedlings of the species that first hit the field to grow.

However, succession does not stop there; a pine appears behind the aspen; and the last - slowly growing shade-tolerant species, such as spruce or oak. A hundred years later, on this site, the community that was on the site of the field to the attention of the forest and plowing is being restored.

VEILIK- a genus of perennial herbaceous plants of the Cereals family, or Bluegrass

Fig. 8.7. Secondary succession of the Siberian dark coniferous forest (fir-cedar taiga) after a devastating forest fire.

1.4 Duration of succession

The duration of succession is largely determined by the structure of the community. A study of primary succession in places such as sand dunes suggests that, under these conditions, menopause requires many hundreds of years. Secondary successions, for example, in clearings, are much faster. Nevertheless, it takes at least 200 years for a forest to recover in a temperate, humid climate.

If the climate is especially harsh (as, for example, in the desert, tundra or in the steppe), the duration of the series is shorter, since the community cannot significantly change the adverse physical environment. Secondary succession in the steppe, for example, lasts about 50 years.

The main stages of secondary succession in a temperate climate:

· The first stage of herbaceous vegetation lasts about 10 years;

· Second stage of shrubs? from 10 to 25 years;

· The third stage of deciduous trees? from 25 to 100 years;

· The fourth stage of conifers? more than 100 years.

Successions can be of various scales. They can go slowly, for millennia, or they can go fast - in a few days.

The duration of succession is largely determined by the structure of the community.

With primary succession, it takes many hundreds of years to develop a sustainable community.

Pay attention!

The need to destroy the parent breed is the main reason for the slow progress of primary successions.

Secondary successions are much faster. This is due to the fact that the primary community leaves behind a sufficient amount of nutrients, developed soil, which creates the conditions for the accelerated growth and development of new settlers.

Example:

In Europe at the end pliocene   (3 million years ago) the ice age began. The glacier destroyed all life under its cover. He tore and smoothed the soil cover, crumbled rocks. With his retreat and climate warming, vast expanses of bare, lifeless land were exposed. Gradually, it was inhabited by various plants and animals. Of course, these changes were very slow. Where the glacier destroyed the rainforests, their restoration continues to the present. These sites have not yet reached a steady state. So they did not have enough for the completion of succession and millions of years.

The changes that led to deciduous forests were also slow. miocene (20 million years ago) to the current northern Central Asian deserts.

Successions pass much faster after a forest fire, when in a certain sequence one biocenosis changes to another, which finally leads to the restoration of a stable community.

Relatively fast fouling of cliffs occurs: sections of rock as a result of erosion or landslide.

The fastest successions are observed in a temporary reservoir or when changing communities in the decomposing corpse of an animal, in a rotting tree trunk, in a hay infusion.

General patterns of succession

In general, the phenomenon of ecological succession can be characterized by the following provisions:

Succession is a natural process, the course of which can be foreseen.

Succession is the result of changes that the communities themselves make in the environment, that is, the process is not set from the outside.

Succession ends with the formation of a climax biocenosis, which is characterized by the greatest diversity, and, therefore, the most numerous connections between organisms.

Thus, the climax biocenosis is maximally protected from possible disturbances by external factors and is in a state of equilibrium.

The main feature of ecological succession is that community changes always occur in the direction of the equilibrium state.

When the ecosystem approaches the final stable state (climax state), in it, as in all equilibrium systems, there is a slowdown in all development processes.

Observations of successions show that some specific properties of biocenoses change in one direction, whatever the type of succession.

We formulate them.

Species of plants and animals are constantly changing.

The species diversity of organisms is increasing.

The size of organisms in the course of succession is growing.

Linear food chains dominated by herbivores turn into complex food chains. Detritious forms (consumers of dead organics) begin to play an increasing role in them.

Biological cycles are lengthening and becoming more complex, organisms are becoming increasingly ecologically specialized.

Organic matter biomass is increasing. There is a decrease in net production of the community and an increase in respiratory rate.

1.5 Significance of succession

A mature community with its great diversity, saturation with organisms, a more developed trophic structure, with balanced energy flows is able to withstand changes in physical factors (such as temperature, humidity) and even some types of chemical pollution to a much greater extent than the young community. However, the young community is able to produce new biomass in much larger quantities than the old. The remnants of civilizations and deserts, the occurrence of which is tied to human activities, are excellent proof that people never realized their close relationship with nature, the need to adapt to natural processes, and not to command them. Nevertheless, even the knowledge that is currently accumulated is enough to make sure that turning our biosphere into one vast carpet of arable land is fraught with great danger. For our own protection, certain landscapes must be represented by natural communities.

Thus, a person can harvest a rich harvest in the form of pure products, artificially supporting the community in the early stages of succession. Indeed, in a mature community, which is at the stage of menopause, net annual production is spent mainly on the respiration of plants and animals and may even be zero.

On the other hand, from the point of view of a person, the stability of a community at the stage of menopause, its ability to withstand the effects of physical factors (and even control them) is a very important and highly desirable property. A person is interested in both productivity and stability of the community. To maintain human life, a balanced set of both early and mature stages of succession, in a state of exchange of energy and matter, is needed. Excessive amounts of food created in young communities can support older stages that help withstand external influences.

Arable land, for example, should be considered young succession stages. They are maintained in this condition thanks to the continuous labor of the farmer. Forests are older, more diverse and more stable communities with low net output. It is imperative that people pay equal attention to both types of ecosystems. If the forest is destroyed in pursuit of temporary income from wood, water reserves will decrease and the soil will be demolished from the slopes. This will reduce district productivity. Forests are valuable to humans not only as suppliers of wood or as a source of additional space that can be occupied by cultivated plants.

Unfortunately, people are poorly aware of the consequences of environmental disruptions arising in pursuit of economic benefits. This is partly due to the fact that even environmental specialists still cannot give accurate predictions of the consequences that various disturbances of mature ecosystems lead to. The remnants of civilizations and deserts, the occurrence of which is due to human activity, are excellent proof that people never realized their close relationship with nature, the need to adapt to natural processes, and not to command them.

Nevertheless, even the knowledge that is currently accumulated is enough to make sure that turning our biosphere into one vast carpet of arable land is fraught with great danger. For our own protection, certain landscapes must be represented by natural communities.

ATTACHMENT:

Indicate the stages of overgrowing of the reservoir from the proposed vegetation: sphagnum, sedge, bog pine, mixed forest, rosemary (sedge, sphagnum, rosemary, bog pine, mixed forest).

Distribute the succession stages in the correct order: annual plants, deciduous shrubs, perennials, conifers (annual plants, perennials, shrubs, deciduous trees, conifers)

Locate the ongoing succession stages in time: populating the territory with mosses. germination of seeds of herbaceous plants, settlement with shrubs, the formation of a sustainable community, the settlement of bare rocks with lichens

1. lichen colonization of bare rocks

2. settlement of the territory with mosses

3. seed germination of herbaceous plants

4. settlement with bushes

5. building a sustainable community

The course of evolution (development) of the community cannot be predicted.

The most common patterns of evolution of biocenoses:

1. Plant and animal species during community development can be predicted

2. Decreasesvariety of species of organisms.

3. Dimensions of organisms in the course of succession are declining.

4, food chains are shortened and simplified.   An increasing role in them begins to play detritophages.

5. Biological cycles get complicated , organisms are becoming more environmentally specialized.

6. Biomass of organic matter during community development increases.   Going on height   community clean products and slowdownrespiratory rate.

1. Continue the definition: “Ecosystem is ...” Options:

1) a collection of various populations that interact for an indefinitely long time, interacting with each other and the environment

2) the relationship between species in the framework of biocenosis

3) the totality of individuals living in the same territory

2. Large terrestrial ecosystems, including smaller ecosystems connected to each other, are called:

1) biocenoses

2) biotopes

3) successions

4) biomes

3. Gross primary production of the ecosystem is called:

1) the total amount of matter and energy coming from autotrophs to heterotrophs

2) the total amount of matter and energy produced by autotrophs

4. Primary production in ecosystems is formed by:

1) producers3) detritophages

2) consumers 4) reducers

5. Secondary products in ecosystems are formed:

3) detritophages

4) reducers

1) producers

2) consumers

3. The lowest productivity is typical for ecosystems:

4) deserts

7. The highest productivity is characteristic for ecosystems:

1) tropical rainforest

2) the central parts of the ocean

3) hot deserts

4) temperate forest

8. Establish in what order ecosystems should be located taking into account the increase in their productivity:

1) central parts of the ocean

3) mountain forests

2) temperate forest

4) coral reefs

1, 3, 2, 4

9. Arrange the following ecosystems in order of increasing productivity:

1) moist forests 3) steppes

2) oak forests 4) arctic tundra

4, 2, 3, 1

10. Despite the fact that the ocean occupies 71% of the area of \u200b\u200bour planet, its production is 3 times less than the production of land plants. Accordingly, the biomass of algae is 10 thousand times less than the biomass of land plants. How to explain this?

(The main producers of land are trees, and the oceans are small unicellular algae; various growths; herbivorous consumers of the ocean quickly eat producers, and the supply of algae is always low, but on land - vice versa)

11. List the principles of ecosystem functioning.

(Obtaining resources and disposing of waste within the cycle of all elements; existence due to almost inexhaustible and clean solar energy; the biomass of the population corresponds to the trophic level occupied by it)

12. Describe the phenomena that indicate a human violation of the principles of ecosystem functioning.

(Disruption of the circulation of substances (pollution, acid rain); the ecosystem functions not only due to solar energy, but also the energy of wind, firewood, fossil fuels and other sources; the principle is violated - there can be no large biomass at the end of long food chains. Man is the third trophic level, that is, it eats meat. So that all people can eat meat, it is necessary to expand the sown area 10 times.)

13. Atmospheric nitrogen is included in the cycle of substances due to activities:

1) chemosynthetic bacteria

2) denitrifying bacteria

3) nitrogen-fixing bacteria

4) nitrate bacteria

14. Sulfur in the form of hydrogen sulfide enters the atmosphere through activities:

1) denitrifying bacteria

2) sulfobacteria

3) methylotrophic bacteria

4) sulfur bacteria

15. Nitrogen enters the plants during the cycle of substances in the form of:

1) nitric oxide 3) nitrates

2) ammonia 4) nitric acid

16. The main anthropogenic sources of sulfur entering the large cycle of substances are:

1) heat power plants

2) fertilizers

3) atomic weapon tests

4) flights of aircraft

17. The cycle of chemical elements between organisms and the environment is called:

1) energy cycle

2) biogeochemical cycle

3) the cycle of living organisms

4) nitrogen cycle

18. Determine which cycle (nitrogen, sulfur cycle) corresponds to each sign (1-6). Set the correspondence between the cycle of substances and their signs:

A, B, A, B, B, A

19. In the terrestrial biocenosis, microorganisms and fungi complete the decomposition of organic compounds into simple mineral components, which are again involved in the circulation of substances by representatives of a certain group of organisms. Name this group:

1) 1st order consumers

3) producers

2) second-order consumers

4) reducers

20. Carbon enters the cycle of substances in the biosphere as a part of:

1) carbon dioxide3) limestone

2) free carbon

21. Carbon leaves the cycle of substances (forming sedimentary rocks) in the composition:

1) calcium sulfate 3) calcium nitrate

2) calcium carbonate

4) calcium sulfide

22. The full cycle of oxygen in nature continues around:

2) 2000 years

3) 1 million years

4) 100 million years

23. The full cycle of water in nature lasts about:

3) 1 million years

4) 100 million years

24. The rule of the edge (border) effect states: at the junctions of biocenoses the number of species in them:

1) does not change

3) decreases

2) increases

4) does not significantly increase

25. The body mass of living organisms in an ecosystem is called:

1) bio-products

3) biomass

2) bioenergy 4) bio-abundance

26. Seasonal periodicity in nature is most pronounced:

1) in the subtropics

3) in temperate latitudes

2) in the deserts 4) in the tropics

27. The frequency of opening and closing oyster shells is referred to the rhythms:

1) daily allowance 3) annual

2) tidal

4) seasonal

28. Leaf fall is referred to the rhythms:

1) moonlight 3) seasonal

2) daily allowance 4) annual

29. The successive change in time of one community by another in a particular area of \u200b\u200bthe environment is called:

1) succession3) menopause

2) fluctuation 4) integration

30. Among the listed examples, primary succession includes:

1) the transformation of abandoned fields into deciduous forests

2) the gradual change of clear-cutting by deciduous forest

3) gradual fouling of bare rock with lichens

4) the transformation of conflagration into spruce

31. Among the listed succession processes, the primary succession includes:

1) the conversion of fires into spruce forests

2) a gradual change of felling by a pine

3) the conversion of degraded pastures into oak forests

4) the appearance on the loose sands of pine

32. Among the listed succession processes, secondary succession is considered:

1) the conversion of abandoned fields into oak forests

2) the appearance of lichens on cooled volcanic lava

3) the gradual fouling of bare rock

4) the appearance on the loose sands of pine

33. The main cause of ecosystem instability is (are):

1) adverse environmental conditions

2) lack of food resources

3) imbalance in the circulation of substances

4) excess of some species

34. A relatively stable state of an ecosystem in which a balance is maintained between organisms, as well as between them and the environment, is called:

1) menopause3) fluctuation

2) succession 4) integration

35. In which ecosystem (A, B) does each of the listed (1-6) species grow?

A, 2-B, 3-B, 4-B, 5-A, 6-A

36. Eutrophication of water bodies is considered:

1) enrichment of water bodies with nutrients that stimulate the growth of phytoplankton

2) the process of turning the swamp into a lake

3) the process of enriching water with oxygen

Theme 7. Biosphere

1. The Earth’s shell, containing the entire totality of living organisms and that part of the planet’s substance that you find: continuous exchange with these organisms, is called:

1) atmosphere 3) ecosphere

2) hydrosphere 4) biosphere

2. Which of the following is not included (in whole or in part) in the biosphere:

1) atmosphere 4) lithosphere

2) magnetosphere5) asthenosphere

3) hydrospheres 6) ionosphere

3. At what height is the so-called separate ozone layer:

1) 20-30 km above sea level

2) 10 15 km above sea level

3) 25-50 km above sea level

4) a separate layer of ozone does not exist

4. The main role of the ozone layer (screen) is:

1) UV protection

2) in maintaining the climate of the planet

3) in creating a greenhouse effect

5. Indicate three substances whose content in the earth's crust is maximum:

1) hydrogen

2) aluminum

3) oxygen

4) calcium

5) silicon

6. Distinctive features of the oceanic crust (compared with the mainland):

1) thickness 3-7 km

2) thickness of 20-40 km

3) a granite layer is present

4) the granite layer is absent

5) sedimentary layer on average less than 1 km

6) sedimentary layer on average 3-5 km

7) the second layer between the sedimentary and basaltic layers

7. Rocks with which more than 76% of the surface of the continents are covered are rocks:

1) igneous

2) sedimentary

3) metamorphic

8. Describe the shells of the Earth that make up the biosphere.

(Atmosphere   (Earth’s gas shell) consists of a mixture of gases: nitrogen, oxygen and inert gases. Its lower layer, up to 15 km, is called the troposphere. At an altitude of 15-35 km from the Earth’s surface is the "ozone screen".

Hydrosphere   (water shell of the Earth) makes up 70% of the Earth’s surface. The largest water reserves are concentrated in the oceans (about 90%). The state of the hydrosphere determines the climatic conditions.

Lithosphere   (hard shell of the Earth) includes the earth's crust and the upper part of the mantle. Life in the lithosphere is concentrated in its upper, fertile layer - the soil.)

9. List the main features of the biosphere that distinguish it from other shells of the Earth.

(Within the biosphere, the geological activity of all living organisms is manifested.

The continuous cycle of substances regulated by the activity of living organisms.

The biosphere receives energy from the sun and therefore is an open system.)

10. List the main functions of the biosphere and give their characteristics.

(The gas function is the release and absorption of gases by living organisms.

No community exists forever, sooner or later it is replaced by another community. This occurs when external factors influence or as a result of environmental changes in connection with the life of the organisms forming biocenoses, including the introduction of new species into the community. Among the diverse forms of bold communities, primary and secondary successions are distinguished. Primary successions are a natural change of communities in territories that are not occupied by vegetation, for example, on sandbanks in river floodplains, in places that were freed up after the retreat of glaciers, etc. Depending on the substrate (its physical and chemical properties), they first settle here or only bacteria, algae and lichens, or vascular plants along with them. [...]

Such community changes are called succession. In the process of primary successions, both natural communities and soil are formed. [...]

The described change of communities occurs within 60-80 years. The stability of such communities is determined by a number of reasons: firstly, the formation of the community by plants with strong environmentally-developing properties, which limit the possibility of introducing new species into it. Moreover, the conditions for the renewal of those species that make up the community are sufficient. Secondly, in sustainable ecosystems there is a well-balanced diverse set of animal species. The interactions of populations in such communities are diverse, well adapted to live together. The possibilities of introducing new species are practically absent. All these properties of a stable community provide him a long existence. [...]

A classic example of a change in communities under the influence of organisms is the process of overgrowing of lakes. In the water of any lake, especially if it is rich in nitrogen and ash elements, a huge number of microscopic organisms (algae, protozoa, etc.) live. When they die, they fall to the bottom along with the fine earth brought into the lake from the slopes. This process, repeating from year to year, leads to the formation of a sapropel at the bottom of the lake, to a decrease in the depth of the lake, to the penetration of sunlight to the bottom of the lake. As a result, conditions are created for the settlement of mosses and multicellular algae, which leads to an acceleration of the accumulation of organic residues at the bottom of the lake (sapropelic peat) and leads to even greater shallowing of the reservoir. And this is accompanied by a settlement of vascular plants with shoots immersed in water or with leaves floating on the surface of the water (buds, water lilies, egg capsules, etc.). The next stage of overgrowing of the lake is the settlement of lake reeds and ordinary reeds, which develop a huge mass of aboveground shoots, from which reed or reed peat is formed after their death. With further filling of the lake with dead plant residues and its shallowing, sedges settle. The lake is gradually turning into a swamp. Observing individual zones of aquatic vegetation on a growing lake, you can restore the main stages of its overgrowing - turning into a swamp. [...]

Similarly, there is a change of communities on glacial deposits in the form of a very thin soil poor in biogenes. Observations in Alaska showed that the formation of a phytocenosis begins with mosses and sedges; after them, creeping, and then shrubby willow forms are included in the community. Later (about 20-25 years later), oleaginous trees appear; after them appears spruce, which forms the basis of the final community in the form of a mixed forest, forming about 100 years after the start of succession. [...]

Progressive changes in the community lead to a change of one community to another. The reason for such shifts could be factors that have been operating in the same direction for a long time, for example, the drying up of wetlands as a result of land reclamation, increasing anthropogenic pollution of water bodies, and increased cattle grazing. Changes in one biocenosis resulting from this are called exogenetic. If at the same time the structure of the community is simplified, the species composition is impoverished, productivity is reduced, then such a change in the community is called digression. However, the change of one biocenosis to another can occur as a result of processes occurring within the community itself, as a result of the interaction of living organisms with each other. [...]

This is a specific form of community change, consisting in the sequential use of various types of decaying organics. The peculiarity of such successions is that the communities consist only of heterotrophic organisms, and the course of successions is directed towards an increasingly structural and chemical simplification of accumulations of organic matter. [...]

So, succession is a regular, sequential change of communities in ecosystems, due to the influence of a complex of internal and external factors. Changes in time are a natural property of ecological communities. The influence of a complex of factors causes succession in ecosystems as an adaptive reaction. F. Clements believed that succession ends with the formation of a community that is most adapted to the complex of climatic conditions, which he called “menopause - formation” or simply “menopause”; At present, this formation is considered a temporary state: in the process of secular changes in conditions (climate and other environmental factors), full-scale ecosystem changes occur. Progressive successions are distinguished, in which species diversity is gradually increasing, but there are also digressions - regressive successions aimed at uniting and simplifying communities. Especially often, the latter began to manifest itself in the presence of large-scale adapted effects on biocenoses that violate the optimum conditions. [...]

The development of biocenoses, in which there is a substitution in time of one community by another, is called ecological succession1. In most cases, succession processes occupy time intervals measured in years and decades, although in some cases community changes follow at a faster rate (for example, in temporary water bodies). Along with this, secular changes in ecosystems are known, reflecting the general evolutionary paths of the biosphere. [...]

To evaluate these diversity measures, Wilson and Schmid chose four criteria: number of community shifts, additivity, independence from alpha diversity, and independence from oversampling. The degree of measurement by each index of species change was estimated by calculating the β-diversity for two hypothetical gradients, one of which is homogeneous (t. [...]

When vegetation is destroyed without changing soil conditions, the community changes in the direction of returning to the state characterizing the initial root type. For example, when coniferous forests are destroyed on deforestation or burnt areas, grasses (reedweeds, ivan-tea, etc.) grow first, and then small-leaved plantations (birch, aspen) gradually form, under the canopy of which spruce or other conifers settle, which subsequently come out into the first tier and form plant communities similar to those that existed before the violation. [...]

The succession problem has been worked out most deeply on phytocenoses, primarily because community changes are based on the functions of autotrophs, while heterotrophic changes are secondary and follow autotrophs. [...]

To the west of the Rocky Mountains, large lowland areas are covered with thickets of semi-desert shrubs. Wormwood communities rise to the lower parts of the foothills; Higher on the slopes are scattered bushes of undersized juniper. Even higher in the mountains, where the juniper grows larger and larger and grows with edible pine, open low-shoot woodlands are formed with a cover of cereals and shrubs in the lower tier. With further ascent into the mountains, the light forest closes more and more, and individual yellow pine trees appear in it. Further, the abundance of edible pine and juniper decreases, and the yellow pine increases, and a pine forest forms. Gradually, yellow pine gives way to douglas and monochromatic fir, which in turn are replaced by forests of Engelman spruce and Alpine fir. Then, when passing through the uppermost belt of mountain forests, the trees decrease in size and turn into shrubs, forming curtains among meadow vegetation. Above the forest border are alpine meadows of highlands. They extend upward, but do not form a continuous cover with height and eventually give way to communities of lichens with few grasses huddling among the rocks. [...]

In those cases when the main species - environmental formers - fall out of the biocenosis, this leads to the destruction of the entire system and the change of communities. Sometimes such changes in nature are made by none other than man, cutting down forests, over-catching fish in water bodies, etc. [...]

F. Clements’s statement about the exceptional importance of climate as a driving force for successions did not stand the test of time. Changes in communities can also occur under the influence of other factors, such as changes in topography, soil, hydrological regime, etc. The most important in modern ecology is given to biocenotic succession factors: plant species (as well as animals) participating in succession communities change habitat for other species, thus "preparing the ground" for the subsequent stage of succession. [...]

Energy resource in developing and mature ecosystems. As the succession passes, an increasing share of available nutrients accumulates in the biomass of the community, and their content in the abiotic component of the ecosystem (soil or water) decreases accordingly. In a young forest, excess biomass is produced, which accumulates in the form of wood (respiration does not destroy all products, and it forms faster than it oxidizes). In the forest, this can be observed firsthand: in the course of succession, tree trunks thicken from year to year. The upper limit of biomass accumulation is achieved when the total respiratory loss (I) becomes almost equal to the total primary productivity (P), that is, the P / I ratio approaches unity. As communities change in the late stages of succession, productivity increases, however, when switching to a climax community, overall productivity usually decreases (Fig. 2.33). [...]

The trophogenic series is a series of growing substrate richness from quartz sand and apigotrophic peat to various loamy and carbonate deposits with the corresponding regular change of communities from poor pine forests to rich oak forests, buchins, fir trees and spruce spruce trees mixed with ischro-deciduous woody pores. Throughout this series, as the trophicity of deposits increases, the light-loving oligo-mesotrophs are successively replaced by shade-tolerant mesotrophs and megatrophs with a constant increase in the overall productivity of plant groups. [...]

The dynamics of an ecosystem is a change in an ecosystem (biogeocenosis) under the influence of external forces and internal processes of its development. The secular dynamics of the ecosystem is distinguished - relatively reversible or irreversible changes in communities caused by various (periodic) factors that occur over a very long (many centuries) time interval. The seasonal dynamics of ecosystems, as a rule, is associated with a change in the seasons of the year and represents one of the forms of cyclic (periodic) changes in the community (daily, seasonal, weather, temperature, etc.). They also distinguish the anthropogenic dynamics of the ecosystem, that is, the change of communities under the influence of human activity (succession). [...]

General concepts of successions. The development of the problem of successions began in botany, and to this day the main provisions of this concept are based on the study of phytocenoses. This is determined not only by historical reasons, but also by the fact that community changes are based on the functions of autotrophs. The heterotrophic component of biocenoses is formed on the basis of phytocenosis and only secondarily begins to affect its composition and properties. [...]

In the reservoirs of the river. Volga values \u200b\u200bof the pigment index E48o / E664 vary in the same range, the average is close to unity (Table 19), indicating that phytoplankton functions within its physiological norm. In the seasonal cycle, the predominance of carotenoids over chlorophyll is noted at the beginning of summer (E480 / E664\u003e 1), which is typical for periods of decline in the development of algae when changing communities. In August, the pigment index decreases and fluctuates around unity. In October, the Е48о / Ебб4 values \u200b\u200bremained unchanged in the Gorky and Cheboksary reservoirs, but significantly increased in Kuibyshev, Saratov and Volgograd. As noted above, the pigment index is characterized by the same trends as the percentage of chlorophyll derivatives. A change in both indicators corresponds to the degree of development of phytoplankton. During seasonal highs, viable active cells are present in the reservoir, the signs of physiological well-being of which are the decreased pigment characteristics: the predominance of green pigments over yellow ones (E480 / E664 is lower or slightly higher than unity), as well as the presence of an active form of chlorophyll (low relative content of pheopigments) . At low concentrations of chlorophyll, indicating a decline in community development, both indicators increase. [...]

If the perturbing factor, after which the development of biocenoses begins, manifests itself with a certain frequency, then they talk about cyclic succession. It is a biological consequence of the influence of the climatic factor external to the biocenosis. In cyclic successions, it is not biocenoses that change the habitat, namely, the variability of the physical environment is a factor determining the change of communities in biocenoses at different phases of the natural cycle.

Relations between organisms in a biocenosis

The following types of consortia are distinguished:

- individual (single plants),

- coenopopulation (population of the species in the plant community),

- regional

- species.

Relations between organisms in a biocenosis are also determined by the time they spent in the community.

They can be permanent (sessile) and temporary (vagil). Constancy characterizes mainly plants, since animals in most cases stay in the community temporarily during the day, season or during the migration period.

According to Beklemishev, interspecific relations are divided into four types: trophic, topical, foric and fabric.

Trophic connections arise when one species eats another (either living individuals, or their remains and waste products).

Forest is a separate biocenosis. Photo: Scott Wylie

Topical connections characterize any physical or chemical change in the living conditions of one species as a result of the activity of another. They consist in creating one type of medium for another, in forming a substrate, in influencing the movement of water, air, in changing temperature, saturating the environment with waste products, etc.

Foricheski - the participation of one species in the distribution of another.

Fabric relations - when one species uses for its construction products isolation or the remains or even living individuals of another species.

The dynamics of biocenoses

In general, the community is characterized by daily, seasonal (annual) and long-term dynamics, characteristic of both plants and animals. The daily, caused by the change in the light and dark parts of the day, in plants is manifested in the intensity of photosynthesis, respiration, opening and closing of flowers, in animals - in different daily activities (daytime, twilight and nighttime).

Often animals change their community during the day. Thus, a heron feeds in shallow water bodies of water, and nests and sleeps in tree crowns, pollinating insects (for example, bees) can fly from a forest community to a meadow.

The seasonal dynamics of the biocenosis depends on the phenological state of the phytocenosis, the species composition, and the number of animals living in it. Each type of plant organism undergoes certain stages of development during the growing season (the beginning of the growing season, flowering, fruiting and dying). In the phytocenosis, consisting of many species, the phases of plant development may coincide and not coincide.

The appearance of phytocenosis, changing throughout the year with the alternation of development phases, is called the aspect. As a rule, the aspect is repeated from year to year with constant sequence, reflecting the color scheme of the plant community (spring bright greens, summer bloom and autumn variegation of forests). The aspect is usually referred to by plants that give the phytocenosis the most noticeable color, for example, the blue aspect of the marsh forget-me-not, the white aspect of the cotton grass, the brown aspect of the sedge leaves, etc.

The seasonal dynamics of animal representatives of the biocenosis is associated with their reproduction, vital activity and migrations. The spring arrival and fall of birds, the spawning of fish, the appearance of young animals, the activity of pollinating insects in the meadows, and the hibernation of a bear are only a negligible fraction of examples of the seasonal dynamics of the animal population of the biocenosis.

The long-term dynamics of the community is caused by its repeated changes over several years in the absence of a sharp change in the species composition. Changes affect mainly the number of individuals of the species forming the biocenosis. As an example, one can cite the changes in the forests of some nature reserves in Belarus and Russia, due to an increase in the number of moose, the main consumer of wood-shrub fodder. Elk eats about 7 tons of feed per year, more than half of which are shoots of deciduous and coniferous species. With an increase in animal density, spoilage of the undergrowth increases. There comes a period when in the forest stands the young generation of the forest stand is almost completely destroyed. Because of the feedless environment, moose are forced to leave such areas of the forest.

Stages of the formation of biocenoses

The emergence of biocenosis begins with the appearance of the first organisms in areas deprived of life (lava flows, volcanic islands, screes, exposed rocks, sand deposits and dried bottoms of water bodies). Settlement begins with the accidental introduction of organisms from territories already developed by them and depends on the properties of the substrate. This site for many plant seeds and animals that have entered here may not be suitable for propagation. Often, especially in the humid zone, the first settlers are representatives of algae, mosses and lichens.

As a rule, only a few of the introduced plant species successfully develop. Consumer animals settle a little later, since their existence without food is impossible, but their accidental visit to the developed areas is a fairly common occurrence. This stage of development of the biocenosis was called pioneer. Although the community has not yet formed at this stage (inconsistent species composition, sparse vegetation cover), it already affects the abiotic environment: soil begins to form.

The pioneer stage is replaced by an unsaturated one, when the plants begin to renew (by seed or vegetatively), and the animals multiply. Not all ecological niches are occupied in an unsaturated biocenosis.

Gradually, the rate of settlement of the site increases due to both an increase in the number of individuals of pioneer vegetation before the formation of thickets, and the introduction of new species. The species composition of such a community is still unstable, new species are introduced quite easily, although competition is beginning to play a significant role. This stage of development of the biocenosis group.

With the subsequent development of the community, the differentiation of the vegetation cover by tiers and synusias occurs, its mosaic, species composition, food chains and consortia become stable. In the end, all ecological niches are occupied and the further introduction of organisms becomes possible only after the crowding out or destruction of old-timers. This final stage of biocenosis formation is called saturated. However, the further development of the biocenosis does not stop and random deviations in the species composition and relationships both between organisms and the environment can still take place.

Random deviations in the structure of the biocenosis are called fluctuations. As a rule, they are caused by random or seasonal changes in the number of species included in the biocenosis as a result of adverse meteorological events, floods, earthquakes, etc. Heavy snowfalls and hoarfrost, for example, lead to thinning of crowns, and in spring under the forest canopy more development cereals. Spring frosts and late spring snow cover not only damage flowering plants, which affects their fruiting, but also often cause mass death of migratory birds. Strong winds, floods and earthquakes cause disturbances in biocenoses, after which it takes a long time to restore the community.

Although the biocenosis is a rather conservative natural system, however, under the pressure of external circumstances, it can give way to another biocenosis. The successive change in time of some communities by others in a certain part of the environment is called succession (from Lat successia, succession). As a result of succession, one community is successively replaced by another without a return to its original state. Succession is caused by the interaction of organisms, mainly wounds, with each other and with the environment.

Successions are divided into primary – historical. Primary occur on primary soil-free Soils - volcanic tuff and lava fields, loose sands, rocky placers, etc. As the phytocenosis develops from the pioneer stage to saturated soil, the soil becomes more fertile and more and more chemical elements are involved in the biological cycle in increasing quantities. With increased fertility, plant species developing on nutrient-rich soils displace less demanding species in this regard. At the same time, the animal population is also changing. Secondary successions occur in the habitats of the destroyed communities, where the soil and some living organisms have been preserved. Destruction of biocenoses can be caused by natural processes (hurricanes, showers, floods, landslides, prolonged droughts, volcanic eruptions, etc.). as well as changes in the living environment by Organisms (for example, when a reservoir overgrows, the aquatic environment is replaced by peat deposits). Secondary successions are characteristic of degraded pastures, fires, deforestation, excluded from agricultural use of arable land and other lands. as well as for artificial plantations. For example, often under the canopy of middle-aged pine crops on sandy loam soils, abundant natural regeneration of spruce begins, which eventually displaces the pine, provided that the next clear cutting of the pine stand and forest cultivation are not carried out. On burned areas with loamy and loamy soils, pioneer vegetation from willow tea and warty birch is replaced by spruce plantations over time.

In recent decades, large-scale drainage and irrigation works have gained particular importance in changing the vegetation cover. In the swamp forests, which are in the zone of influence of drainage channels, hygrophytes plants disappear (sedge ols, for example, are transformed into nettles). The transformation of the species composition, including the animal population, also affects forests that come to drained swamps. Irrigation land reclamation, on the contrary, promotes the active penetration of plants of the hygrophilic and mesophilic groups into waterlogged areas as a result of the accumulation of water used for irrigation. Industrial pollution also has a noticeable effect on biocenoses. All these changes are secondary successions.

The change of one biocenosis to another during succession forms a succession series, or series. The study of succession series is of great importance in connection with the increasing anthropogenic impact on biocenoses. The end result of this kind of research can be the prediction of the formation of natural and anthropogenic landscapes. The study of secondary succession and the factors causing them plays an important role in solving the problems of the protection and rational use of biological and land resources.

If the natural course of succession is not disturbed, the community gradually comes to a relatively stable state in which equilibrium is maintained between organisms, as well as between them and the environment, to menopause. Without human intervention, this biocenosis can exist indefinitely, for example, blueberry pine, lichen tundra on sandy soils.

The concept of menopause was developed in detail by the American botanist X. Kauls and is widely used in foreign botanical and geographical literature. According to this concept, menopause is the terminal stage in the evolution of the community, to which the soil of a certain type corresponds - pedoclimax. Successions leading to this stage are called progressive, and those that remove the biocenosis from it are called regressive. It is impossible, however, to give the concept of menopause its absolute meaning and to assume that upon reaching it, the community stops developing.

Biocenoses, which, when disturbed, return to their original state, are called indigenous. Birch forest will grow at the place where the blueberry pine or sorrel spruce has been cut down, and it, in turn, will again be replaced by blueberry pine or sorrel spruce. In this case, we are talking about the indigenous types of forests.

Transformed biocenoses do not return to their original state. So, the lowland sedge swamp drained and developed for agricultural crops after the depletion of the peat deposit and the destruction of the reclamation network with the cessation of agricultural use for some reason develops in the direction of the formation of birch or alder small forests. The zoocenosis of this small forest is different from the animal species community of the open grass swamp.

Classification of biocenoses

In order to scientific knowledge of biocenoses and the practical application of knowledge about them, the community of organisms must be classified according to their relative dimension and complexity of the organization.

The classification is designed to put in order all their diversity with the help of a system of taxonomic categories, i.e., taxa, combining in this case groups of biocenoses with varying degrees of commonality of individual properties and characters, as well as structure and origin. In this case, a certain subordination of simple taxa to complex taxons, taxa of small (local) dimension to taxa of planetary dimension, and the gradual complication of their organization should be observed. In addition, the classification of biocenoses should take into account the presence of possible boundaries between them.

There are no particular difficulties in establishing boundaries when neighboring biocenoses have clear indicative signs. For example, an upland bog with a rosemary – moss cover and a short pine stand contrasts with the surrounding pine forest community on sandy soils. The border between the forest and the meadow is also clearly visible. However, since the conditions for the existence of communities change more gradually than the communities themselves, the boundaries of biocenoses are usually blurred. The gradual transition from one phytocenosis to another with their proximity and the change of one phytocenosis to another in time is reflected in the concept of a continuum (from Latin continuum - continuous) of vegetation developed by the Soviet geobotanist L.G. Ramensky, an American ecologist P. X. Whittaker.

Borders between communities are sharper in those cases when edificators have the greatest transformative effect on the environment, for example, the boundaries between forests, formed by different tree species - pine, spruce, oak and others. In the steppes, semi-deserts, and deserts, the boundaries between communities are more gradual, since the environmentally transforming role of grassy species is less contrasting.

The classification of communities uses taxonomic categories adopted in plant geography and based on the identification of dominants and edificators, which indicates the recognition of phytocenosis as an ecological framework that determines the structure of biocenosis. The taxonomic system of communities constructed by dominants and edifiers can be expressed as follows: association - group of associations formation group of formations class of formations type of biome - biocenotic cover.

The lowest taxonomic category is association. It is a combination of homogeneous microbiocenoses with the same structure, species composition and similar relationships between organisms and between them and the environment. In the field, the main signs of its isolation are: the same tier addition, similar mosaic (spotted, scattered), the coincidence of dominants and edificators, as well as the relative homogeneity of the habitat. The name of the association for multi-tiered communities consists of the generic names of the dominant tier dominant (condominants) and edificators in each tier, for example, juniper-mossy pine, spruce birch-bilberry, etc. The name of complex meadow associations is formed by listing the dominants and subdominants, and the dominant is called the last , for example, edulute-meadow-bluegrass association. Usually meadow associations are indicated in Latin: Ranunculus + Roa pratensis.

A group of biocenotic associations is formed by associations that differ in the composition of one of the tiers. Blueberry pine, for example, combines associations with the undergrowth of juniper, buckthorn and undergrowth of birch. The group of cereal – small-sedge – grass-related associations includes meadow communities with a set of the mentioned groups of meadow grasses (cereals, small sedges, forbs).

The biocenotic formation includes groups of associations. The formation is distinguished by the dominant, according to which it is called: the formation of common pine, black alder, pedunculate oak, white saxaul, cauliflower, wormwood, etc. This is the main unit of medium rank, widely used in mapping forest vegetation.

A group of formations is all formations whose dominants belong to the same life form. Since the life forms of plants are extremely diverse, the volume of the groups of formations is heterogeneous: dark coniferous, light coniferous, deciduous, evergreen, small-leaved and broad-leaved forests; coarse-grained, fine-grained, low-cereal, finely grassed and other groups of meadow formations.

A class of formations is formed by all groups of formations whose dominants have ecologically close life forms, for example, coniferous forests (with a needle plate), deciduous forests, etc.

The biome type (biocenotic type) unites the classes of formations. Types of biomes are tundra, forest-tundra, taiga, meadows, steppes, deserts, prairies, tropical rain forests, etc.

Biocenotic cover is the highest taxonomic unit, including all types of land biomes.

In the botanical and geographical literature, there are other classifications of phytocenoses. For an aquatic environment in which the role of vegetation is limited, the identification of taxonomic categories of biocenoses is based on the animal population.

Each biogeocenosis has its own spatial structure, which in the vertical direction is expressed in tiers, and in the horizontal in synusias. The ongoing interactions and interchanges of the components of the biogeocenosis (atmosphere, soil and rock, water, the animal and plant world and microorganisms) determine its continuous development, which leads to the replacement of some biogeocenoses by others - to successions. Ultimately, the destruction of some communities and the creation of new ones determines the continuous development of the biogeocenotic cover of the Earth. Over time, the continuous change in an individual biogeocenosis slows down, as the process of the introduction of new organisms weakens and the menopause begins.

The self-development of biogeocenosis, determined by internal (endogenous) processes, is disrupted by external (exogenous) influences, as a result of which new succession series arise. Among the most important exogenous factors is human activity, but the person himself is not one of the components of biogeocenosis.

Biogeocenoses are the unit cells of the biogeosphere (biogeocenotic cover) - the shell of the Earth in which the living matter of the planet is concentrated. The biogeosphere is the only shell of the Earth in which the constant presence and normal comprehensive human activity are possible.