Reasons for stability and change of succession ecosystems. Reasons and sequence of change from one biogeocenosis (ecosystem) to another

In our world there are such concepts as unstable and stable ecosystems. Stable ecosystems are taiga, feather grass steppe, etc. But gray meadows, rather small bodies of water, wastelands - all this tends to change. They are gradually covered with other vegetation, which leads to the need to reorganize the animal type; accordingly, the self-development of the ecosystem is formed. And the basis for self-development is precisely environmental conditions and changes caused by the passage of time.

Reasons for the self-development of ecosystems

The main reason for the systematic self-development of an ecosystem, or in other words, the instability of a given system, is the aspect of imbalance in the circulation of substances;
In biocenoses, the activities of some species cannot be compensated by the activities of another type; accordingly, environmental conditions will certainly change;
As for the population, it is precisely this that changes the environment in an unfavorable direction; over time, the aspect of displacement of one species by another is formed, until a more stable system is formed, but it is not eternal;
All processes of self-development will initially exist until a balanced community is formed, which will be able to maintain the necessary balance of substances in a particular ecosystem.

Thus, we can confidently say that the process of self-development of an ecosystem itself has a lot of features. In nature, the development of these systems occurs precisely because of the presence of an unstable state in relation to a more stable one. Processes of this type are called succession.

Why does ecosystem self-development occur?

As we have already said, the development of ecosystems is affected by imbalance, as well as the passage of time. For example, if you look at a small lake for a significant amount of time, you can see how it is gradually overgrown with grass and certain plants. Due to the lack of incoming oxygen, the complete decay of dying plants does not form, which is precisely why peat deposits are formed. Over time, such a lake becomes shallow, overgrown at the edges, and turns into a small swamp. Afterwards, a wet meadow forms in place of the lake; the passage of time transforms the meadow into an area brightly planted with shrubs; the bushes gradually transform into forests.

Succession can begin on almost any land area that is formed as a result of some reason. Among other things, it should immediately be noted that this process occurs as a result of a number of natural stages. Each stage has already been described by many scientists. Throughout the development of the ecosystem, it inevitably changes, and the changes are natural and natural; they have all been studied and described in sufficient detail by researchers.

To ensure that self-development does not remain an empty phrase, you definitely need to turn your attention to modern literature. You can argue as much as you like that modern man...

Remember!

What are the relationships between all the organisms that make up one ecosystem?

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

Reasons for the stability of ecosystems. Each ecosystem is a dynamic structure consisting of hundreds and even thousands of species of producers, consumers and decomposers, connected to each other by a complex network of food and non-food relationships. The stability 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 maintains its integrity.

Each species within an 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 have an adverse effect on some species, their numbers decrease, and they may completely disappear from the ecosystem. Such a targeted increase or decrease in the number of individuals of any population can lead to changes 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 may occur. 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 basic food will decrease, but this will not lead to automatic restoration of vegetation in the ecosystem.

Only a non-living system can be absolutely unchanged and static. Even in the most stable ecosystems, certain changes occur depending on the season, time of day, and 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 that are 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 remains in equilibrium. If 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, it will disappear. In both cases, the balance will be disrupted, causing a change in the community. These changes can affect species diversity, food chain structure, productivity and other indicators of the system, which will ultimately lead to a change in ecosystems.

Change of ecosystems. This process consists in the fact that in a certain area in a strictly defined sequence there is a natural change in populations of various species. 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 overgrowing of a small lake (Fig. 80).

First, a raft 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, in 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 form, the lake gradually becomes shallow and turns into a swamp. Subsequently, the swamp overgrows at the edges, turning into a meadow, and later into a forest. Thus, the species composition of both plant and animal parts of the ecosystem changes completely. A forest ecosystem is being formed on the site of the former lake.

Rice. 80. Change of communities when a reservoir becomes overgrown. 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 (D)

Ecosystems always strive to maintain equilibrium, therefore, when ecosystems change, 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, and 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 stable community will be forest, in others - steppe, and in still others - tundra. Over time, conditions on the globe gradually change in one direction or another, and the community that was stable during a certain period of historical development will, after thousands of years, give way to another stable community, whose structure corresponds to the changed conditions. Thus, more than 10 thousand years ago, during the era of the last glaciation, in the place of the current broad-leaved deciduous forests there was tundra.

Apart from 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 species diversity for the sustainability of an ecosystem?

2. What is the equilibrium state of an ecosystem?

3. Give examples of rapid changes in ecosystems.

4. What determines the final stage of ecosystem development?

Think! Do it!

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

2. Explain what the unreasonable and random acclimatization of new species leads to. Give examples that you know from botany and zoology courses.

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 for this work. Create a map of biogeocenosis and plot the distribution areas of the main species on it. Are there species included in the Red Book in this biocenosis? Evaluate species diversity indices.

Work with computer

Refer to the electronic application. Study the material and complete the assignments.

Succession. When studying the development and changes of ecosystems, ecologists use the concept of “succession.” succession is a natural, directed process of change in communities as a result of the interaction of living organisms with each other and with the abiotic environment surrounding them. There are two types of ecological successions: primary successions occur on a substrate that initially does not contain organic matter, for example, on bare rock or a solidified lava flow; secondary– grow on substrates from which the communities that previously existed on them have been removed, for example, overgrowing of an abandoned field.

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Reasons for changing ecosystems. Observing the same biogeocenosis, you can see how its appearance noticeably changes throughout the year. The scorched steppe at the end of summer is not like the same steppe in spring, colorful with blooming tulips, irises, primroses, and crocuses. The winter forest, dressed in snow caps, is completely different from the autumn forest, painted in orange, yellow, and crimson colors. The appearance of the meadow changes as different grasses bloom on it in spring and summer. At the same time, in addition to seasonal changes, long-term changes also occur in ecosystems.

Despite the fact that an ecosystem is a stable, self-regulating system, it is characterized by development. The development of any system is understood as an irreversible qualitative change, which is usually accompanied by quantitative changes. Thus, in the process of ecosystem development, simple communities in it are replaced by more complex ones, with a rich species composition, with complex spatial and trophic structures. That is, the development of an ecosystem is based on the change of communities (plant, animal, fungal, microbiological) that are part of the biocenosis of a given ecosystem.

The development and change of communities can be observed on molehills, which overgrow in a series of successive stages over several years. Soil exposures formed as a result of the fall of old trees take longer to recover - tens of years. Large deforestation or areas after fires require 100-200 years to recover.

Changes in natural communities can occur under the influence of biotic factors and humans.

Change of ecosystems under the influence of the vital activity of organisms

The change of communities under the influence of the vital activity of organisms lasts hundreds and thousands of years. Plants play the main role in these processes.

An example of a change in community under the influence of the vital activity of organisms is the process of overgrowing of water bodies. Most lakes gradually become shallow and decrease in size. Over time, the remains of aquatic and coastal plants and animals, as well as soil particles washed away from the slopes, accumulate at the bottom of the reservoir. Gradually, a thick layer of silt forms at the bottom. As the lake becomes shallower, its shores become overgrown with reeds and reeds, then with sedges. Organic residues accumulate even faster and form peaty deposits. Many plants and animals are replaced by species whose representatives are more adapted to life in new conditions. Over time, a different community forms in place of the lake - a swamp. But the change of communities does not stop there. Shrubs and trees that are unpretentious to the soil may appear in the swamp, and ultimately the swamp may be replaced by a forest.

Thus, a change in communities occurs because, as a result of changes in the species composition of communities of plants, animals, fungi, and microorganisms, the habitat gradually changes and conditions favorable for the habitat of other species are created.

It has been noted that the process of changing communities tends to end with the stage of a mature community: with a rich species composition, branched food networks, and the ability to self-regulate. As a result, a stable ecosystem is formed - one that is in relative balance with the environment.

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

26. Reasons for sustainability and change of ecosystems

Remember!

What are the relationships between all the organisms that make up one ecosystem?

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

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

Review questions and assignments

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

2. What is the equilibrium state of an ecosystem?

3. Give examples of rapid changes in ecosystems.

4. What determines the final stage of ecosystem development?

Think! Do it!

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

2. Explain what the unreasonable and random acclimatization of new species leads to. Give examples that you know from botany and zoology courses.

Work with computer

Refer to the electronic application. Study the material and complete the assignments.

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Stability and change of ecosystems (biogeocenoses).

Question 1. What is the importance of species diversity for the sustainability of an ecosystem?
The diversity of the species composition of biocenoses ensures the real existence of not so much chains as food networks, 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 interweaving, the more stable the biocenosis. Indeed, in complex chains with high species diversity, the ecological capabilities of different species complement and compensate for each other. As a result, even with significant changes in environmental conditions, the complex system maintains its integrity. The most dangerous (from the point of view of instability) for the ecosystem is a decrease in the biomass of producers, as well as damage at the level of such biotope elements as soil, water, air.

Question 2. What is the equilibrium state of an ecosystem?
The equilibrium state of the ecosystem means that the biomass (primary production) synthesized by green plants and other autotrophs meets the needs of the ecosystem in energy terms. With a decrease in the needs of consumers and decomposers, the accumulation of organic matter begins, and with an increase, its consumption begins. The result of accumulation is, for example, the deposition of peat. Overconsumption leads to a decrease in the number of consumers, and in some cases to radical environmental changes (goats brought to small tropical islands destroyed the original vegetation and led to the transformation of forests into semi-desert).

Question 3. Give examples of rapid change in ecosystems(biogeocenoses) .

An example of a rapid change of ecosystems is the overgrowing of a lake. First, raft is formed near the coast - a surface layer of moisture-loving and aquatic plants. Then peat accumulates, gradually filling the bowl of the reservoir. As a result, the lake disappears, replaced by a swampy shallow forest.
If a pine forest is replaced by a spruce forest, spruce seeds entering the pine forest first develop under the pine crowns. Then, when the spruce trees 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 pine trees in the forest are replaced by spruce trees; The lower tiers also change: shrubs and grasses are replaced by mosses that are resistant to lack of light and high humidity.
Another example is the overgrowth of a place where there was a forest fire. In this case, in central Russia, within a relatively short time, there is a consistent change in the main producers: grasses - shrubs - deciduous trees - coniferous trees.

Question 4. What does the final stage of ecosystem development (biogeocenosis) depend on?
The final stage of ecosystem development depends on climatic (primarily annual temperature fluctuations and precipitation), soil and topographic conditions. For example, in polar latitudes the typical ecosystem is 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 reservoir are of utmost importance.
In our time, due to the drying out of the Aral Sea, the existing water balance of this small sea has been disrupted. Until 1960, the Aral Sea had a noticeable “damping” effect on the climate of the adjacent territories. By absorbing heat in the summer and releasing it into the surrounding deserts in the winter, the sea moderated temperature extremes and stabilized living conditions biocenoses Aral region. Moisture evaporated by the sea reduced the dryness of the air and the deficiency of moisture available to living organisms. After the 60s of the last century, there was a progressive decline in the level of the Aral Sea: by 1979, its water area decreased by 16 thousand km 2 by 1985 -
by 19 thousand km 2. In subsequent years, with every meter of sea level decline, up to 2 thousand km 2 of its bottom was exposed.
The drop in sea water level entails a decrease in the groundwater horizon - up to 4 m at the mouth of the Amu Darya and up to 6-11 m in the Kyzylkum desert. The dry seabed is dominated by saline-sand massifs. In general, there is an intensive process of desertification, in which the leading factors are surface salinization of the soil and wind activity, which determines the widespread transfer of salt particles.
The listed 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. The saline-sandy plains are initially (in the second year after exposure) colonized by saltworts. Gerbils, small jerboas, and house mice move here; Following them, some predators appear here (weasel, fox, steppe polecat). Ungulates also appear - wild boar, and 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. A drop in groundwater levels entails an expansion of the zone of loose sand; the degree of aridization increases. All this affects the species composition, numbers and conditions of existence in the adjacent territories of the Kyzylkum, Aral Karakum, and Ustyurt plateaus.
Over time, conditions on Earth (especially for terrestrial ecosystems) change, which leads to a change in biocenoses.

Reasons for stability and change of succession ecosystems. Reasons and sequence of change from one biogeocenosis (ecosystem) to another

Reasons for the self-development of ecosystems

Why does ecosystem self-development occur?

Change of ecosystems under the influence of the vital activity of organisms

Stability and change of ecosystems (biogeocenoses).

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