Reasons for the sustainability of ecosystems. Development of a biology lesson on the topic "Causes of stability and change of ecosystems" (Grade 11). What will happen during the change of biogeocenosis

- a self-regulating system, but their steady state is never fully achieved. Communities of organisms change over time, with changes affecting species diversity, quantitative indicators, the structure of food chains, productivity, etc.

Variability of biogeocenosis it is mainly manifested in a change in the number of individual species and in a change in biogeocenoses. The population size depends on the ratio of born and dying individuals. An increase in the birth rate leads to both an increase in the number and a decrease in death. Both of these indicators depend on many that act in different directions. Therefore, the population is constantly fluctuating. Fluctuations in abundance for different species are different. To study population fluctuations, it is necessary to know in detail the biology of the species and environmental factors, as well as to determine the limiting factor. Significant population fluctuations are observed in simpler ecosystems.

Change of biogeocenoses- long process. This is its main difference from seasonal fluctuations in indicators. In a certain habitat, a regular change of populations of various species occurs in a strictly defined sequence. This process is called ecological succession. A stable community is characterized by balance. This means that the total production of organisms in terms of energy exactly corresponds to the energy costs that are used to ensure the vital activity of the organisms included in the community. Therefore, in such a system it remains constant, and the system itself remains in equilibrium. If the costs in the ecosystem become less than the gross primary production, then there will be an accumulation of organic matter, if more - its disappearance. In any case, the imbalance will cause changes in the community - populations of some species will be replaced by populations of others.

Agrocenoses- artificial, created by man for his own purposes by sowing or planting and further cultivating cultivated plants, as well as using areas for intensive grazing of domestic animals. One of the main features of agrocenosis is that one or a very small number of plant species clearly predominates. The species diversity of animals is reduced in them, since only species that feed on certain plants can live here. Having no biological competitors, these animals can multiply intensively and become pests that threaten the existence of agrocenosis. In the agrocenosis, the effect of natural selection is weakened and mainly artificial selection is in effect, aimed at maximizing the productivity of plants that humans need. Agrocenosis is unstable, if it is not supported, it will quickly collapse.

Agrocenoses differ significantly from natural biogeocenoses. The main features of the existence of agrocenoses are the following:

Agrocenoses are characterized by low species diversity, since the main component of this ecosystem is one plant species, artificially maintained by humans.
Usually, agrocenosis exists for 1–2 seasons, since crop rotation is typical for cultivated areas. And, as you know, a change in the main biotic component of an ecosystem leads to a change in the type of ecosystem.
Organisms living within the agrocenosis and not related to the objects of human economic activity experience a constant impact and are forced to adapt to them.
The use of new technologies for growing agricultural plants contributes to the increase in the productivity of agrocenoses. Industrial technology, which is based on the latest achievements in biological and other fields of science, is becoming more and more widely used. Industrial technology is characterized by a high specialization of the economy, the use of the achievements of selection, agrochemistry, crop production, the use of high-performance equipment that works taking into account the biological characteristics of agricultural plants.

In order to preserve the land, a minimum number of tillage is carried out so that heavy equipment does not destroy the soil structure. So, pre-sowing tillage is combined with the introduction of highly effective and rapidly decomposing chemicals for the destruction of weeds. Industrial technology requires the cultivation of highly productive varieties and plants in the fields, the introduction of optimal doses of organic and mineral fertilizers.

The most important condition for the application of industrial technology is the placement of crops according to the best predecessors. For example, the corn precursor must be removed from the field early so that the soil can be thoroughly worked in the fall, weeds cleared from the field, and an adequate supply of moisture in the soil can be ensured. The predecessor of corn should not have pests or pathogens in common with it. These requirements are met by legumes, which enrich the soil with nitrogen, as well as potatoes.

An important condition for obtaining high yields is the timely implementation of all agricultural work. It is impossible to be late with sowing seeds, carrying out agrotechnical measures to care for plants, and harvesting.

The use of industrial technology for growing crops contributes to a significant increase in the productivity of agrocenoses.

Page 156. Remember.

1. What relationships are associated with all organisms that are part of one ecosystem?

No organism in nature exists outside of ecosystems. And this is manifested primarily in the presence of a huge number of relationships of a given organism with other organisms and with abiotic factors. These connections are the basic condition for the life of organisms and their communities. Through these connections, the mechanisms of the circulation of biogenic substances, the mechanisms of energy transfer, and the mechanisms of ecosystem stability are realized. These connections are so perfected by the course of the evolutionary process that the violation of at least one of them can lead to a chain of irreversible consequences up to the death of the ecosystem, more precisely, up to a radical restructuring of its structure or replacement by another ecosystem, usually poorer. Relationships between organisms can be divided into interspecific and intraspecific. We will consider intraspecific relationships in more detail when studying population dynamics. Here we will focus on interspecific relationships that have the greatest impact on the organization of ecosystems. These relationships are usually classified according to the "interests" on which organisms build their relationships:

1. food (trophic) links - form the trophic structure of the ecosystem, which we have already considered earlier; in addition to relations when some organisms serve as food for others, this also includes relations between plants and insect pollinators of flowers, competitive relations due to similar food, etc .; this is the most common type of connection;

3. phoric connections (from the Latin word foras - out) - relations for the distribution of seeds, fruits, etc.;

4. factory connections (from the Latin word fabricato - manufacturing) - the use of plants, fluff, wool to build nests, shelters, etc.

2. What energy supports the constant circulation of substances in the ecosystem?

All living organisms in the process of life are in constant and active interaction with the environment. The essence of this interaction is the exchange of matter and energy. The vital activity of an ecosystem and the circulation of substances in it are possible only under the condition of a constant supply of energy. The main source of energy on Earth is solar radiation. The energy of the Sun is translated by photosynthetic organisms into the energy of chemical bonds of organic compounds. The transfer of energy through food chains obeys the second law of thermodynamics: the transformation of one type of energy into another occurs with the loss of part of the energy. At the same time, its redistribution is subject to a strict pattern: the energy received by the ecosystem and assimilated by producers is dissipated or, together with their biomass, is irreversibly transferred to consumers of the first, second and other orders, and then to decomposers with a drop in the energy flow at each trophic level. As a result, there is no circulation of energy.

Page 158. Questions for repetition and tasks.

1. What is the importance of its species diversity for the sustainability of an ecosystem?

The diversity of the species composition of biocenoses ensures the real existence of food networks rather than chains, since at each trophic level there are organisms of different species that can replace each other in performing the functions of the biotic cycle of substances when the ecological situation changes. The more diverse the food chains and the more complex their interlacing, the more stable the biocenosis. Indeed, in complex chains with high species diversity, the ecological capabilities of different species complement and compensate each other. As a result, even with a significant change in environmental conditions, a complex system retains its integrity. The most dangerous (in terms of violation of stability) for the ecosystem is a decrease in the biomass of producers, as well as damage at the level of such elements of the biotope as soil, water, and air.

2. What is the equilibrium state of the ecosystem?

The equilibrium state of the ecosystem means that the biomass (primary production), which is synthesized by green plants and other autotrophs, meets the needs of the ecosystem in terms of energy. With a decrease in the needs of consumers and decomposers, the accumulation of organic matter begins, with an increase - its consumption. The result of accumulation is, for example, the deposition of peat. Excess consumption leads to a decrease in the number of consumers, and in some cases to radical ecological changes (goats brought to small tropical islands destroyed the original vegetation and led to the transformation of forests into a semi-desert).

3. Give examples of rapidly changing ecosystems.

An example of a rapid change in ecosystems is the overgrowth of a lake. First, a quagmire is formed off the coast - a surface layer of moisture-loving and aquatic plants. Then there is the accumulation of peat, gradually filling the bowl of the reservoir. As a result, the lake disappears, giving way to a swampy small forest.

In the case of a change from a pine forest to a spruce forest, spruce seeds that fall into a pine forest first develop under pine crowns. Then, when spruces grow tall enough, they begin to inhibit the growth of light-loving pines. Spruce is a shade-tolerant plant and continues to develop well. Over time, the pines in the forest are replaced by spruces; the lower tiers also change: shrubs and grasses are replaced by mosses that are resistant to lack of light and high humidity.

4. What determines the final stage of ecosystem development?

The final stage of ecosystem development depends on climatic (primarily annual fluctuations in temperature and precipitation), soil and topographic conditions. For example, in the polar latitudes, a typical ecosystem is the tundra, in the temperate zone - mixed forests, in the mountains at an altitude of 2-3 km - alpine meadows. In the case of aquatic ecosystems, the temperature and salinity of the water, the depth and type of the water body are of paramount importance.

In our time, due to the drying up of the Aral Sea, the existing water balance of this small sea has been disturbed. Until 1960, the Aral Sea had a noticeable "damping" effect on the climate of the adjacent territories. Absorbing heat in summer and releasing it to the surrounding deserts in winter, the sea softened extreme temperature expressions and stabilized the living conditions of the biocenoses of the Aral Sea region. The moisture evaporated by the sea reduced the dryness of the air and the lack of moisture available to living organisms. After the 60s of the last century, there was a progressive decrease in the level of the Aral Sea: by 1979, its water area had decreased by 16 thousand km2; by 1985, by 19 thousand km2. In subsequent years, with each meter of sea level drop, up to 2 thousand km2 of its bottom was exposed. The drop in the water level in the sea entails a decrease in the groundwater horizon - up to 4 m at the mouth of the Amudarya and up to 6-11 m in the Kyzylkum. Salty-sand massifs predominate on the dried bottom of the sea. In general, there is an intensive process of desertification, in which the leading factors are the surface salinization of the soil and wind activity, which determines the wide transfer of salt particles. These changes affect the state of the ecosystems of the territory adjacent to the former coast in a strip of up to 300 km or more. Saline-sandy plains are initially (in the second year after exposure) colonized by saltwort. Gerbils, small jerboas, house mice move here; after them, some predators appear here (weasel, fox, steppe polecat). Ungulates also appear - wild boar, in some places - saiga and goitered gazelle. But after 3-4 years, these places turn into plump salt marshes, devoid of vegetation and animal population. The fall in the groundwater level entails the expansion of the zone of free-flowing sands. All this affects the species composition, abundance and conditions of existence in the adjacent territories of the Kyzyl Kum, Aral Karakum, Ustyurt plateau. Over time, conditions on Earth (especially for terrestrial ecosystems) change, which leads to a change in biocenoses.

Think and do.

1. Explain what causes unreasonable and accidental acclimatization of new species. Give examples that you know from courses in botany and zoology.

Here is a raccoon dog, which was brought to Central Russia in the middle of the last century because of its fur. The raccoon dog felt great in the places where it was settled. She accepted this offer of a man, moreover, raccoon dogs began to multiply very quickly, began to displace foxes from their usual habitats, began to deprive them of their food supply. Another example is the mollusk rapan, which was brought to the seas of the Old World from the American shores on the bottoms of ships. Now he has bred incredibly in the Black Sea and devoured the entire population of mussels. Now you can hardly find large mussels there.

In nature, there are both stable and unstable ecosystems. Oak grove, feather grass steppe, dark coniferous taiga spruce forests are examples of long-term, sustainable ecosystems . Wastelands, wet meadows, shallow waters, if left to their own devices, change rapidly. They are gradually overgrown with other vegetation, inhabited by other animals and turn into ecosystems of a different type. A forest grows on the site of a swamp, a steppe is restored on abandoned arable land, etc.

The main reason ecosystem instability - unbalanced circulation of substances.

If in biocenoses the activity of some species does not compensate for the activity of others, then environmental conditions will inevitably change. Populations change the environment in an unfavorable direction for themselves and are forced out by other species for which the new conditions are more environmentally beneficial. This process continues until a balanced community, which is able to maintain the balance of substances in the ecosystem.

Thus, in nature, ecosystem development from an unstable state to a stable one. This process is called succession . For example, the overgrowth of small lakes can be traced back over one or more generations of people (Fig. 78). Due to the lack of oxygen in the bottom layers, decomposing organisms are not able to ensure the complete decay of dying plants. Peaty deposits are formed, the lake becomes shallow, overgrown from the edges and turns into a swamp. It is replaced by a wet meadow, a meadow by shrubs, and then by a forest.

succession begins on any piece of land that has been exposed as a result of any reason: on screes, shallows, loose sands, bare rocks, rock heaps created by man, etc. It passes a series regular stages.

- At the first stage the exposed area is populated by organisms from the surrounding habitats that accidentally get here: seeds, spores, flying and crawling insects, settling rodents, birds, etc. Not all of them are able to take root in this place, and many either die or leave it.

- At the second stage accustomed species begin to develop and change their habitat without interfering with each other.

- At the third stage when the site is fully developed, competitive relations become aggravated. Since species change the environment in an unfavorable direction for themselves, some of them are forced out and new ones appear. For example, in a soddy area, seeds of weeds that were the first to develop this area can no longer germinate. They disappear. The process of gradual change in the species composition can last quite a long time.

- At the final stage finally, a permanent composition of the community is established, when species are distributed among ecological niches without interfering with each other, connected by food chains and mutually beneficial relationships, and coordinately carry out the cycle of substances. In such a biocenosis, regulatory ties are strong, and it can support the ecosystem indefinitely until external forces take it out of this state.

Thus, self-development of ecosystems carried out through the relationship between species and their impact on the environment, i.e. through regular changes in biocenoses.

Change of biocenoses in successions it always goes from the least stable state to the most stable one. The rate of these changes is gradually slowing down. Slowing down is one of the main features of succession. Approaching a stable state, they can linger for a long time at separate stages. A shallow reservoir overgrows faster than subsequently the birch forest in this place is replaced by oak.

Unstable stages when changing biocenoses are called immature communities, sustainable - mature.

Directed changes in biocenoses also begin if there are any partial disturbances in an already formed ecosystem. They lead to its restoration, therefore they are called recovery shifts or secondary successions.

For example, after a fire in a spruce forest, spruce cannot regenerate immediately, since its seedlings cannot withstand the competition of light-loving and fast-growing herbs: fireweed (willow-herb), reed grass, etc. Grasses are replaced by raspberry thickets and undergrowth of light-loving deciduous trees, and only under them canopy in the shade, young Christmas trees begin to grow. Each of these stages of development is longer and more stable than the previous one. The process of spruce forest restoration takes several decades in nature.

The development of biocenoses during succession is characterized by a number of general patterns :

Gradual increase in species diversity,

Change of dominant species,

The complexity of food chains,

An increase in the proportion of species with long development cycles in communities,

Strengthening mutually beneficial ties in biocenoses, etc.

The total biomass and production of plants is gradually increasing, but the scale of the use of these products in food chains is also growing. All this leads to a slowdown in the pace of change and to the establishment of stable ecosystems.

In mature, stable communities, everything that plants grow is used by heterotrophs - this is the main reason for the stabilization of ecosystems. If a person removes products from such ecosystems (for example, wood from mature forests), he inevitably violates them.

At the initial stages of the development of biocenoses, until food chains have developed, an excess of plant production is created in ecosystems, and such biocenoses are beneficial to humans.

People activities constantly leads to changes in various biocenoses - as a result of logging, drainage and watering of lands, development of peat bogs, laying roads, etc. Partial or deep disturbances of ecosystems are caused by natural processes of their self-healing.

However, natural possibilities are not unlimited. Self-healing of biocenoses often hampered by various external causes. For example, annual floods of rivers all the time disrupt the formation of stable biocenoses on their banks, and here communities exist in a constantly immature state. Similarly, the constant plowing of the fields prevents the restoration of natural vegetation in the area. Wastelands may not be populated by plants or animals for decades if any factor strongly deviates from the norm, for example, highly toxic upturned rocks, high soil density, or insufficient moisture.

Another reason in violation of the recovery capabilities of biocenoses - a decrease in species diversity in the environment. If there is nowhere to take plant seeds or animal species that play an important role in the corresponding stages of community development, the ecosystem remains at a less stable stage.

For example, during clear-cutting of spruce forests over large areas, they overgrow with time with low-value small-leaved species and linger in this state for a long time, since there is nowhere to get spruce seeds from.

Ability to manage the processes of self-development and self-recovery of ecosystems- a very important task of modern economic activity, when a person sets in constant motion the entire living cover of the planet. By removing the limiting factors, supplying the appropriate plant seeds and instilling the necessary animal species, it is possible to accelerate the formation of stable communities or, conversely, delay the processes at the stage of development we need.

Agroecosystems, the main differences from natural ecosystems.

Artificial biocenoses created by people involved in agriculture are called agrocenoses . They include the same components of the environment as natural biogeocenoses, have high productivity, but do not have the ability to self-regulate and stability, because depend on human attention to them.

Agroecosystem (agrobiocenosis)

An artificial, man-made biocenosis, a community of living organisms that serves to obtain agricultural products and is regularly maintained by man.

1. Fewer species live in an agroecosystem than in a natural ecosystem. Therefore, food chains in the agroecosystem are short, unbranched, because of this, the circulation of substances is unstable, therefore, itself agroecosystemunstable. If a person does not take care of it (water, fertilize, weed), then it will collapse, for example, a wheat field will overgrow, turn into a meadow. Thus, the natural ecosystem receives energy only from sunlight, and the agroecosystem receives energy from the Sun and from humans (the main source of energy for the agroecosystem is still the Sun).

2. Lives in the agroecosystem many plants of the same species(monoculture), therefore, good conditions are created for consumers that feed on this species (viruses, bacteria, nematodes, mites, insects, etc.). Therefore, in agriculture, it is imperative to deal with pests. Main ways:

• pesticides (plus - cheap, minus - natural enemies of pests are destroyed, so that their number may, on the contrary, increase);
• biological methods (use of natural enemies - riders against butterflies, ladybugs against aphids, etc.);
• crop rotation (each year a different crop is grown on the field so that pests do not accumulate in the soil)

3. In a natural ecosystem, plants take mineral salts from the soil with their roots, then the plants are eaten by consumers, destroyed by decomposers, and the salts return back to the soil - this is a closed cycle of substances. On the wheat field, the crop is harvested and exported, and mineral salts are not returned to the soil ( open circulation of substances). Therefore, fertilizers are used in agriculture - mineral (salts) and organic (manure).

In an agrocenosis (for example, a rye field), the same food chains, as in the natural ecosystem: producers (rye and weeds), consumers (insects, birds, voles, foxes) and decomposers (bacteria, fungi). Man is an essential link in this food chain.

Agrocenoses, in addition to solar energy, receive extra energy, which a person spent on the production of fertilizers, chemicals against weeds, pests and diseases, on irrigation or drainage of land, etc. Without such an additional expenditure of energy, the long-term existence of agrocenoses is practically impossible.

In agrocenoses, it acts mainly artificial selection directed by man, first of all, at the maximum increase in crop yields.

In agroecosystems, sharply reduced species diversity living organisms. One or several species (varieties) of plants are usually cultivated in the fields, which leads to a significant depletion of the species composition of animals, fungi, and bacteria.

Thus , compared to natural biogeocenoses agrocenoses:

They have a limited species composition of plants and animals,

Incapable of self-renewal and self-regulation,

Exposed to the threat of death as a result of mass reproduction of pests or pathogens

They require tireless human activity to maintain them.

Thematic tasks

A1. The fastest way to the succession of biogeocenosis can lead

1) the spread of infections in it

2) increased rainfall

3) the spread of infectious diseases

4) human economic activity

A2. Usually the first to settle on the rocks

2) lichens

4) shrubs

A3. Plankton is a community of organisms:

1) seated

2) hovering in the water column

3) sedentary bottom

4) fast floating

A4. Find wrong statement.

The condition for the long-term existence of an ecosystem:

1) the ability of organisms to reproduce

2) the influx of energy from the outside

3) the presence of more than one species

4) constant regulation of the number of species by humans

A5. The property of an ecosystem to be preserved under external influences is called:

1) self-reproduction

2) self-regulation

3) resistant

4) integrity

A6. The stability of an ecosystem is enhanced if it:

2) the number of decomposer species decreases

3) the number of species of plants, animals, fungi and bacteria is increasing

4) all plants disappear

A7. The most sustainable ecosystem:

1) wheat field

2) orchard

4) cultural pasture

A8. The main reason for the instability of ecosystems:

1) imbalance of the circulation of substances

2) self-development of ecosystems

3) the permanent composition of the community

4) population fluctuations

A9. Point out the wrong statement. The change in the species composition of trees in the forest ecosystem is determined by:

1) environmental changes caused by community members

2) changing climatic conditions

3) the evolution of community members

4) seasonal changes in nature

A10. During the long development and change of the ecosystem, the number of species of living organisms included in it,

1) gradually decreases

2) gradually grows

3) stays the same

4) it happens in different ways

A11. Find the wrong statement. In a mature ecosystem

1) species populations are well reproduced and are not replaced by other species

2) the species composition of the community continues to change

3) the community is well adapted to the environment

4) the community has the ability to self-regulate

A12. A purposefully created human community is called:

1) biocenosis

2) biogeocenosis

3) agrocenosis

4) biosphere

A13. Point out the wrong statement. The agrocenosis left by man dies, because.

1) competition between cultivated plants intensifies

2) cultivated plants are crowded out by weeds

3) it cannot exist without fertilizers and care

4) it does not withstand competition with natural biocenoses

A14. Find the wrong statement. Signs characterizing agrocenoses

1) greater diversity of species, more complex network of relationships

2) obtaining additional energy along with solar

3) inability to long-term independent existence

4) weakening of self-regulation processes

IN 1. Choose signs of agrocenosis

1) do not support their existence

2) consist of a small number of species

3) increase soil fertility

4) get extra energy

5) self-regulating systems

6) there is no natural selection

IN 2. Find the correct sequence of events when vegetation colonizes rocks:

1) shrubs

2) scale lichens

3) mosses and bushy lichens

4) herbaceous plants

A specific biogeocenosis does not exist forever. Sooner or later it is replaced by another. Changes occur under the influence of changes in the environment by living organisms themselves, with a change in climatic conditions, in the process of evolution of life on Earth, under the influence of man.

Self-development and ecosystem change. As an example of a change in the environment under the influence of living organisms themselves, let us consider the settlement of rocks by vegetation. At the first stages of settlement, weathering of rocks is of great importance: destruction, partial dissolution, and changes in the chemical properties of minerals. Already at the very initial stages, the role of the first settlers is great: bacteria, blue-green algae, scale lichens. Blue-green algae, free-living algae and algae in the composition of lichens are producers - creators of organic matter. Many blue-green algae fix nitrogen from the air and enrich it with an environment that is still unsuitable for life. Lichens dissolve the rock with secretions of organic acids and contribute to the accumulation of mineral nutrition elements. Bacteria and fungi destroy organic matter created by producers.

Organic matter is not completely mineralized. A mixture of various organic and mineral compounds and plant residues enriched with nitrogen gradually accumulates. Conditions are created for the settlement of mosses and bushy lichens. The process of accumulation of organic matter and nitrogen is accelerated, a thin soil layer is formed. A primitive community is formed, capable of existing in an unfavorable environment.

The first settlers are well adapted to the harsh conditions of bare rocks - they can withstand dryness, and heat, and frost. Slowly but steadily they change their habitat and thus create conditions for the introduction of other populations. With the advent of herbaceous plants (sedges, cereals, clover, bluebell, etc.), competition for water, light, and nutrients is becoming tougher. Pioneer settlers in this struggle are forced out by newcomers. Shrubs settle behind the grasses, which hold the soil together with their roots. Herb and shrub communities are replaced by forest ones.

During the long development and change of the ecosystem, the number of species of living organisms included in it gradually increases. The community becomes more complex, its food web more and more extensive. The diversity of relationships between organisms is increasing, and the community is making fuller use of the resources of the environment. There comes the stage of a mature community, the most well adapted to the surrounding conditions and possessing self-regulation. Populations of species in a mature community reproduce well and are not replaced by other species.

Described ecosystems change over thousands of years. However, there are changes taking place before the eyes of one generation of people, for example, the overgrowth of shallow reservoirs.

Change of ecosystems under the influence of man (anthropogenic factor). A powerful factor in changing ecosystems is human economic activity. Human impact on natural ecosystems began a long time ago. It has been increasing all the time along with the increase in the population of the Earth. In the last century, due to the rapid development of industry, agriculture, and the growth of cities, human influence has become decisive. Big changes are taking place, for example, in the "green zones" around cities, which are used for recreation by citizens. The vegetation of such a territory is constantly trampled down by people walking in the forest, picking berries and mushrooms. The above-ground organs of plants are injured, the soil is compacted, and its ability to retain moisture is reduced. All these factors have a negative effect on forest grasses, in which the rhizomes are located directly under the forest floor.

Strong trampling damages the undergrowth of trees. In shrubs and mature trees, the tops begin to dry, they are easily affected by fungal diseases and pests. As a result, the forest thins out, brightens up. Favorable conditions are created for the introduction of meadow grasses, which are photophilous and are less afraid of trampling, as they form turf. Forest grasses become uncompetitive and fall out of the herbage.

It greatly changes meadow, steppe and desert ecosystems, where there is intensive grazing. Animals eat certain types of grasses, which leads to the spread of "not eaten" plants. Hellebore, sorrel, eryngium, and wormwood grow on pastures. The abundance of valuable, in terms of fodder, cereals is decreasing. Many plants do not have time to bloom and produce seeds. The number of species is reduced, the community is simplified. Perennial grasses are replaced by annual plants, the root systems of which are less developed. The soil, not held back by the roots, begins to be washed away by streams of water or blown by the wind. The destruction of the soil leads to the depletion of the environment in nutrients and water, which sharply worsens the living conditions of plants and reduces their productivity. Rich multi-grass highly productive meadows and steppes, with excessive grazing, turn into poor wastelands.

The change of biogeocenoses under the influence of the anthropogenic factor is the fastest. It occurs over several years, and often abruptly. Such abrupt changes include deforestation, plowing of land with the creation of agrocenoses, the construction of reservoirs, when land ecosystems turn into water ones.

Change of ecosystems under the influence of abiotic factors. The climate of the globe has changed many times. With warming in ecosystems due to natural selection, more heat-loving species of plants, animals and microorganisms began to predominate, and with cooling, cold-resistant ones. Periods with low precipitation were characterized by an increase in the number of organisms resistant to lack of moisture. Periods with heavy precipitation led to the flourishing of organisms with increased requirements for moisture content.

With climatogenic changes in ecosystems, as a result of natural selection, the number of some species of organisms is reduced, their range is reduced, they experience biological regression. Other species, which proved to be more stable in the struggle for existence, increase their numbers, expand their habitat, that is, they experience biological progress.

Biology. General biology. Grade 11. Basic level Sivoglazov Vladislav Ivanovich

26. Causes of sustainability and change of ecosystems

Remember!

What are the relationships between all organisms that are part of the same ecosystem?

What energy maintains the constant circulation of substances in an ecosystem?

Reasons for the sustainability of ecosystems. Each ecosystem is a dynamic structure consisting of hundreds and even thousands of types of producers, consumers and decomposers, connected with each other by a complex network of food and non-food relationships. The sustainability of an ecosystem depends on its species diversity and the complexity of food chains. The more complex and branched the chains, the more stable the existence of the ecosystem. The ecological capabilities of different species complement and compensate each other in such a way that in the event of minor changes in environmental conditions, a complex system retains its integrity.

Each species in the ecosystem is represented by a population, so the stable existence of an ecosystem is determined by the stable existence of its constituent populations. Changes in external conditions affect some species adversely, their numbers decrease, and they may completely disappear from the ecosystem. Such a directed increase or decrease in the number of individuals of any population can lead to a change in the ecosystem as a whole. For example, with a sharp increase in the number of ungulates in the steppe zone, complete destruction of vegetation can occur. The disturbance of the grass cover will cause wind erosion of the soil, and the top fertile layer can be completely destroyed. The number of ungulates in the absence of the main food will decrease, but this will not lead to an automatic restoration of vegetation in the ecosystem.

Only an inanimate system can be absolutely immutable and static. Even in the most stable ecosystems, certain changes occur depending on the season, time of day, weather influences. If these changes reflect certain cyclical processes in the external environment, they do not lead to a directed transformation of the ecosystem. All indicators of such an ecosystem fluctuate around a certain average value, i.e., it is maintained dynamic balance.

The equilibrium state of the ecosystem means that the amount of products synthesized by green plants and other producers corresponds in energy terms to the needs of the ecosystem. In this case, the biomass of the ecosystem remains constant, and the position of the ecosystem is in equilibrium. If the costs in the ecosystem decrease, it will not be able to process all the products, and organic matter will begin to accumulate; if energy costs increase, they will disappear. In both cases, the balance will be disturbed, which will cause a change in the community. These changes can affect species diversity, food chain structure, productivity, and other indicators of the system, eventually leading to a change in ecosystems.

Changing ecosystems. This process consists in the fact that in a certain area, in a strictly defined sequence, a regular change of populations of various species occurs. As a rule, this is a very long process, but sometimes changes in the ecosystem can be traced over the course of several generations. An example of such rapid changes is the overgrowth of a small lake (Fig. 80).

First, a quagmire is formed along the perimeter of the lake - a continuous carpet of floating plants, which, dying, sink to the bottom of the reservoir. In the bottom layers, under conditions of lack of oxygen, decomposers do not have time to process all the dying parts of plants and animal remains. As a result, peat deposits are formed, the lake gradually becomes shallower and turns into a swamp. In the future, the swamp overgrows from the edges, turning into a meadow, and later into a forest. Thus, the species composition of both the plant and animal parts of the ecosystem is completely changed. A forest ecosystem is being formed on the site of the former lake.

Rice. 80. Change of communities during overgrowth of a reservoir. Vegetation moves from the banks to the center of the water surface (A). This process continues, and the lake is gradually filled with peat (B, C). After the lake is completely filled with peat, a forest grows in its place (G)

Ecosystems always strive to maintain balance, therefore, when changing ecosystems, each subsequent stage of development is longer and more stable than the previous ones.

In nature, changes in ecosystems occur constantly and are characterized by certain patterns: species diversity increases, total biomass increases, food chains become more complex. All this gradually leads to the formation of stable communities.

The final stage of ecosystem development depends on climatic, soil, water and topographic conditions. In some areas of the globe, the most sustainable community will be the forest, in others - the steppe, and in others - the tundra. Over time, conditions on the globe gradually change in one direction or another, and the community that was stable at a certain period of historical development will, thousands of years later, give way to another stable community whose structure corresponds to the changed conditions. So, more than 10 thousand years ago, in the era of the last glaciation, tundra was located on the site of the current broad-leaved deciduous forests.

With the exception of earthquakes, landslides, volcanic eruptions and other natural disasters, natural changes in ecosystems occur gradually. However, human intervention often causes abrupt and global changes, leading to disruption or death of ecosystems.

Review questions and assignments

1. What is the importance of its species diversity for the sustainability of an ecosystem?

2. What is the equilibrium state of an ecosystem?

3. Give examples of rapidly changing ecosystems.

4. What determines the final stage of ecosystem development?

Think! Execute!

1. What ecosystems are the most resilient in your area? Explain why this is.

2. Explain what causes unreasonable and accidental acclimatization of new species. Give examples that you know from courses in botany and zoology.

3. Do your research. Study the species composition of plants and animals of one of the most common types of biogeocenoses in your area. Use atlases-determinants for this work. Create a map of biogeocenosis, put on it the distribution areas of the main species. Are there any species included in the Red Book in this biocenosis? Assess the indices of species diversity.

Work with computer

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