Ecological successions. Succession of an ecological system Primary succession in brief
Ecological succession is a change of biocenoses. If a biocenosis is stable, then it exists indefinitely. But we often have to observe how one biocenosis (ecosystem) turns into another: a lake becomes a swamp, and a meadow becomes a forest.
Types of successions
There are two types of succession: primary and secondary.
During primary succession, a new biocenosis is formed in an initially lifeless biotope. In this case, the colonization of rocky or sandy surfaces occurs.
The starting substrates can be:
- volcanic lava;
- sands;
- rocks;
- ravines;
- river sediments, etc.
Of particular importance in the colonization of such substrates is the accumulation of substances available to plants for root nutrition.
Rice. 1. Primary succession.
The first plants and bacteria to colonize lifeless surfaces change their chemical composition due to their metabolism, as well as when they die.
Any succession is long-lasting. Although every year during primary succession an enrichment of the species composition is observed, it will reach a state of stability after tens of years.
Secondary succession is the replacement of one biocenosis by another.
Its most common causes:
- changes in climatic conditions;
- establishing more stable relationships between species;
- human impact;
- change in geological conditions.
Every plant has limiting environmental factors. When the hydrological, soil or weather regime changes, some plants can leave the ecosystem, others can populate, changing its appearance.
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Rice. 2. Secondary succession.
Human activity contributes to the change of biocenoses. For example, in Africa and Asia, due to soil degradation due to livestock grazing, the desert ecosystem is replacing the savanna.
Modern steppes differ significantly in the species composition of plants from the pristine steppes. Therefore, areas of the surviving reference steppes are recognized as protected areas and are protected by law.
Features of succession
Let us consider what the main feature of ecological succession is: only such relationships between organisms and the organisms themselves are preserved over time that cannot be replaced by others under given conditions.
The leading role in the change of biocenoses belongs to plants.
Succession occurs by changing stages.
Stages of succession
Correctly composed ecological succession has the form of successively replacing each other stages.
Succession is an irreversible change in one biocenosis, the emergence of another. It can be caused by any natural phenomena or occur under human influence. Ecological succession was initially studied by representatives of a science such as geobotany. Subsequently, this phenomenon became a subject of interest to other ecologists. The pioneers who revealed the importance of succession were F. Clements, V. N. Sukachev, S. M. Razumovsky. Next, we will analyze the concept in more detail and give a classification. In addition, the article will describe the process using examples.
Terminology
Who introduced the definition? The very concept of “succession” was proposed by F. Clements to define special biological communities that succeed each other over time. They are characterized by the formation of a series or series in such a way that the previous one creates the conditions for the development of the next one. In the case when no factors arise that can provoke another succession, the series ends with a relatively stable community, which is characterized by constant exchange. The formation described above was defined by Clements using the specific term "menopause." According to the scientist, this is a stable community, within which there are no factors contributing to any changes in its development. In this case, the duration of menopause is not important.
Classification
Successions can be ordered according to different principles. Using classification according to various characteristics, various types of successions can be distinguished. Among such characteristics: rate of formation/decay, duration of existence, reversibility, constancy, origin, development trend (progress or degradation), change in the number and diversity of species.
Succession can be classified on many grounds. The grouping process primarily depends on what goal the scientist sets for himself. At the same time, there are types of successions, grouped according to the nature of the processes occurring in a given stable community. On this basis, scientists distinguish two main categories: endogenous and exogenous. What is the difference? Endogenous succession is a change due to the activities of the communities themselves. The root cause of the process is usually an imbalance in exchange. In other words, the change is carried out due to the activity of internal factors. Exogenous succession is a change caused by
Microbiology
In the forest floor, for example, succession can be studied in several stages simultaneously. This possibility is due to the change in direction from top to bottom when moving. In addition, the phenomenon can cause changes in humidity, the content of any special compounds or gases, temperature, etc. The process of soil formation is accompanied by a fairly long-term change in both the plant and microbial communities.
Primary and secondary succession
What do these concepts mean? Let's look further. Primary succession is characterized by the fact that it occurs in a lifeless area. This could be bare rock without vegetation, sandy areas, solidified lava, and the like. When organisms begin to inhabit such areas, their metabolism affects and changes the environment. Then more complex development begins. And then the species begin to replace each other. An example of succession is the formation of the original soil cover, the colonization of an initially lifeless sandy area, first of all by microorganisms, plants, and then fungi and animals. A special role here is played by plant remains and substances formed as a result of the decomposition of organic matter. Thus, the soil begins to form and change, and the microclimate changes under the influence of microorganisms, plants and fungi. As a result, the community of organisms expands. This succession is an ecogenetic change. It is called that because it changes the very territory on which it exists. And the initial appearance of soil in a lifeless area is called syngenetic change.
Substrate humidity
This indicator influences the type of succession. Thus, the following groups are distinguished:
- Xerarchal, on an anhydrous substrate.
- Psammoxeroseria, on the sands.
- Litoxeroseria, on rocky terrain.
- Geoxeroseria, on dry clay or loam.
- Mesarchic if the substrate has quite significant moisture.
- Hydraarchic if the substrate is extremely wet.
Primary succession occurs in several stages. Interesting examples of succession can be given. For example, in a forest zone, a lifeless and dry substrate is replaced first by lichens, then by moss, then by herbs (annual plants), after which perennial shrubs, trees, and grasses begin to develop the territory. There are other examples of succession. Thus, the settlement of the territory of solidified lava after eruptions or a slope after an avalanche is often mentioned.
Process flow
The development of primary succession occurs simultaneously with soil formation. The process is influenced by the ingress of seeds from outside, the death of seedlings that are not resistant to extreme conditions, and (from a certain time) one or another community develops or is replaced mainly due to the difference in nitrogen content in the soil and the degree of destruction of its mineral part. In soil and other natural microbial communities, succession is a phenomenon usually caused by the supply of a certain portion of an organic compound in one form or another. Since microorganisms adapt either to the destruction of various complex polymers, or the absorption of any monomers at high concentrations, or to existence in severe conditions of hunger, structural changes in the community are observed during the destruction and during the use of organic matter.
Secondary successions
These processes lead to the colonization of the territory by species after some damage. For example, a forest partially destroyed by fire. The territory where it was previously located retained the soil and seeds. A grass community will be formed literally next year. And then they appear. Under the cover of an aspen or birch forest, spruce trees begin to grow, subsequently displacing deciduous trees. The restoration of dark coniferous trees occurs within approximately 100 years. But the forest in some areas is being cut down again. Due to this, recovery does not occur in such areas.
Continuumism and structuralism in the study of biological communities
Although the definitions that Clements postulated are widely used in science, there are two paradigms that differ significantly from each other. Let's look at them in more detail. Within each of these paradigms, the meaning of Clements's definitions is different. How do these approaches differ? Followers of the structuralist paradigm strongly support Clements' conclusions and continue to develop his theory. Continualists, on the contrary, do not agree with the actual existence of such phenomena as biological communities, succession, climax, post-climax, and climax continuum. In the latter paradigm, ecosystem processes are reduced to the interaction of various categories with each other. These species, according to continuumism, randomly begin to interact with each other and with inanimate nature. How did continuism come about? The fact is that there is not one author of this theory: this paradigm was born almost simultaneously in two countries, in two independent scientific communities: with L. G. Ramensky in the USSR and G. Gleason in the USA.
The role of successions in the formation and change of the biosphere
Thanks to successions, the study of which continues in geobotany to this day, soil cover is formed, its composition changes, and once lifeless areas are populated, first by microorganisms, and then by plants, fungi and animals. The study of the patterns and mechanisms by which both primary and secondary changes in communities occur clearly shows that it is impossible to predict in advance unambiguously which species will replace each other in the chain. However, replacement of biological communities more often occurs in ways that increase in the study area.
4. Ecological succession
The relatively long existence of a biocenosis in one place (pine or spruce forest, lowland swamp) changes the biotope (the place where the biocenosis exists) so that it becomes unsuitable for the existence of some species, but suitable for the introduction or development of others. As a result, a different biocenosis, more adapted to new environmental conditions, gradually develops in this biotope. Such repeated replacement of some biocenoses by others is called succession.
succession (from Latin successio - continuity, inheritance) is a gradual, irreversible, directed replacement of one biocenosis by another in the same territory under the influence of natural factors or human influence.
The term “succession” was first used by the French botanist De Luc in 1806 to refer to changes in vegetation.
Examples of succession are the gradual overgrowing of loose sand, rocky placers, shallows, the colonization of abandoned agricultural lands (arable land), fallow lands, clearings, etc. by plant and animal organisms. Former fields are quickly covered with a variety of annual plants. This also includes seeds of tree species: pine, spruce, birch, aspen. They are easily carried over long distances by wind and animals. In lightly turfed soil, seeds begin to germinate. Light-loving small-leaved species (birch, aspen) find themselves in the most favorable position.
A classic example of succession is the overgrowing of a lake or river oxbow and its transformation first into a swamp, and then, after a long period of time, into a forest biocenosis. At first, the water surface becomes shallow, covered with raft on all sides, and dead parts of plants sink to the bottom. Gradually, the water surface is covered with grass. This process will last several decades, and then a high peat bog will form in place of the lake or oxbow lake. Even later, the swamp will gradually begin to be overgrown with woody vegetation, most likely pine. After a certain period of time, the processes of peat formation on the site of the former reservoir will lead to the creation of excess moisture and the death of the forest. Finally, a new swamp will appear, but different from what was before.
Along with the change in vegetation, the fauna of the territory subject to succession also changes. Typical for an oxbow or lake are aquatic invertebrates, fish, waterfowl, amphibians, and some mammals - muskrats, minks. The result of succession is a sphagnum pine forest. Now other birds and mammals live here - wood grouse, partridge, elk, bear, hare.
Any new habitat - an exposed sandy river bank, frozen lava of an extinct volcano, a puddle after rain - immediately turns out to be an arena for colonization by new species. The nature of developing vegetation depends on the properties of the substrate. Newly settled organisms gradually change their habitat, for example, by shading the surface or changing its humidity. The consequence of such environmental changes is the development of new, resistant species and the displacement of previous ones. Over time, a new biocenosis is formed with a species composition noticeably different from the original one.
In the beginning, changes happen quickly. Then the rate of succession decreases. Birch seedlings form dense growth that shades the soil, and even if spruce seeds germinate along with the birch, its seedlings, finding themselves in very unfavorable conditions, lag far behind the birch ones. Light-loving birch is a serious competitor for spruce. In addition, the specific biological characteristics of birch give it advantages in growth. Birch is called the “pioneer of the forest,” a pioneer species, since it is almost always the first to settle on disturbed lands and has a wide range of adaptability.
Birches at the age of 2 - 3 years can reach a height of 100 - 120 cm, while fir trees at the same age barely reach 10 cm. Gradually, by 8 - 10 years, birches form a stable birch stand up to 10 - 12 m high. Under the developing The spruce begins to grow along the canopy of the birch, forming undergrowth of varying degrees of density. Changes also occur in the lower, grass-shrub layer. Gradually, as the birch crowns close, light-loving species, characteristic of the initial stages of succession, begin to disappear and give way to shade-tolerant ones.
The changes also affect the animal component of the biocenosis. At the first stages, May beetles and birch moths settle in, then numerous birds - chaffinch, warbler, warbler, small mammals - shrew, mole, hedgehog. Changing lighting conditions begins to have a beneficial effect on young Christmas trees, which accelerate their growth. If at the early stages of succession the growth of fir trees was 1 - 3 cm per year, then after 10 - 15 years it already reaches 40 - 60 cm. Around 50 years, the spruce catches up with the birch in growth, and a mixed spruce-birch stand is formed. Animals include hares, forest voles, mice, and squirrels. Succession processes are also noticeable among the bird population: orioles that feed on caterpillars settle in such a forest.
The mixed spruce-birch forest is gradually replaced by spruce. The spruce outstrips the birch in growth, creates significant shade, and the birch, unable to withstand the competition, gradually falls out of the tree stand.
Thus, succession occurs, in which first a birch and then a mixed spruce-birch forest is replaced by a pure spruce forest. The natural process of replacing birch forest with spruce forest lasts more than 100 years. This is why the process of succession is sometimes called century-long change .
If the development of communities occurs in newly formed, previously uninhabited habitats (substrates), where there was no vegetation - on sand dunes, frozen lava flows, rocks exposed as a result of erosion or ice retreat, then such succession is called primary.
An example of primary succession is the process of colonization of newly formed sand dunes where there was previously no vegetation. Perennial plants that can tolerate dry conditions, such as creeping wheatgrass, first settle here. It takes root and reproduces on quicksand, strengthening the surface of the dune and enriching the sand with organic matter. The physical conditions of the environment in close proximity to perennial grasses change. Following the perennials, annuals appear. Their growth and development often contribute to the enrichment of the substrate with organic material, so that conditions suitable for the growth of plants such as willow, bearberry, and thyme are gradually created. These plants precede the appearance of pine seedlings, which establish themselves here and, growing up, after many generations form pine forests on sand dunes.
If vegetation previously existed in a certain area, but for some reason it was destroyed, then its natural restoration is called secondary succession . Such successions can result, for example, from partial destruction of the forest by disease, hurricane, volcanic eruption, earthquake or fire. The restoration of forest biocenosis after such catastrophic impacts takes a long time.
An example of secondary succession is the formation of a peat bog when a lake becomes overgrown. The change in vegetation in a swamp begins with the edges of the reservoir becoming overgrown with aquatic plants. Moisture-loving plant species (reeds, reeds, sedges) begin to grow in a continuous carpet near the banks. Gradually, a more or less dense layer of vegetation is created on the surface of the water. Dead plant remains accumulate at the bottom of the reservoir. Due to the low amount of oxygen in stagnant waters, plants slowly decompose and gradually turn into peat. The formation of a swamp biocenosis begins. Sphagnum mosses appear, on a continuous carpet of which cranberries, wild rosemary, and blueberries grow. Pines can also settle here, forming sparse growth. Over time, a raised bog ecosystem is formed.
Most of the successions currently observed anthropogenic , those. they occur as a result of human impact on natural ecosystems. This is grazing of livestock, cutting down forests, the occurrence of fires, plowing of land, flooding of soils, desertification, etc.
Succession. Examples of ecosystem succession
succession
Types of successions
Secondary succession
Types of successional changes
Duration of succession
Examples of ecosystem succession
Communities are constantly changing. Their species composition, the number of certain organisms, the trophic structure and other indicators of the community change.
Communities change over time.
Succession is a consistent, natural replacement of some communities by others in a certain area of the territory, caused by 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 used to ensure the vital activity of its constituent organisms).
In ecology, the total energy consumption is called - the common breath of the community.
It is clear that in such an ideal case, the production processes are balanced by the respiration processes.
Consequently, the biomass of organisms in such a system remains constant, and the system itself remains unchanged or in equilibrium.
If the “total respiration” is less than the gross primary production, an accumulation of organic matter will occur in the ecosystem;
If it is more, it will be reduced.
In both the first and second cases, community changes will occur
If there is an excess of a resource, there will always be species that can master it, and if there is a shortage, some species will go extinct.
This change is the essence of ecological succession.
The main feature of this process is that changes in the community always occur in the direction of an equilibrium state.
1.1 Types of succession
Succession that begins in a place devoid of life (such as 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 that was not previously occupied by vegetation: bare rocks or frozen volcanic lava.
Example:
Formation of a community on an exposed area of rock, an area of solidified volcanic lava, on a newly formed sand dune, or after the retreat of a glacier.
Only a few plants are capable of living on such soil; they are called pioneers of succession. Typical pioneers are mosses and lichens. They change the soil, releasing acid that breaks down and loosens rocks. Dying mosses and lichens decompose under the influence of decomposer bacteria, and their remains are mixed with a loose rocky substrate (sand).
This forms the first soil on which other plants can grow. The need to destroy the parent rock is the main reason for the slow progress of primary successions; note the increase in soil layer thickness as succession progresses.
On soil poor in nutrients, grasses settle, which are more specifically capable of displacing lichens and mosses. The roots of grasses penetrate into the cracks of the rock, push these cracks apart and destroy the stone more and more.
Grasses are being replaced by perennial plants and shrubs, such as alder and willow. On the roots of alder there 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 becomes more and more fertile.
Now trees can grow on it, such as pine, birch and spruce.
Thus, the driving force of succession is that plants change the soil beneath them, affecting its physical properties and chemical composition, so that it becomes suitable for competing species, which displace the original inhabitants, causing a change in community - succession, due to plant competition They do not always live where conditions are better for them.
Primary succession occurs in several stages.
For example, in a forest zone: dry lifeless substrate - lichens - mosses - annual forbs - cereals and perennial grasses - shrubs - trees of the 1st generation - trees of the 2nd generation; in the steppe zone, succession ends at the grass stage, etc.
1.2 Secondary succession
The term "secondary succession" refers to communities that develop in place of a pre-existing, previously formed community.
In places where human economic activity does not interfere with the relationships between organisms, a climax community develops, which can exist for an indefinitely long time - until any external influence (plowing, logging, fire, volcanic eruption, flood) disrupts its natural structure.
If a community is destroyed, succession begins in it - a slow process of restoring its original state.
Examples of secondary successions: overgrowing of an abandoned field, meadow, burnt area or clearing.
Secondary succession lasts several decades.
It begins with the appearance of annual herbaceous plants in the cleared area of soil. These are typical weeds: dandelion, sow thistle, coltsfoot and others. Their advantage is that they grow quickly and produce seeds adapted to dispersal over long distances by wind or animals.
However, after two or three years they are replaced by competitors - perennial grasses, and then by shrubs and trees, primarily aspen.
These rocks shade the ground, and their extensive root systems take all the moisture from the soil, so that the seedlings of the species that first hit the field find it difficult to grow.
However, succession does not stop there; a pine tree appears behind the aspen; and the last ones are slow-growing shade-tolerant species, such as spruce or oak. A hundred years later, the community that was on the site of the field before the foresting and plowing of the land is being restored on this site.
VEINIK- a genus of perennial herbaceous plants of the Poaceae or Poa family
Rice. 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. Studies of primary succession in places such as sand dunes indicate that, under these conditions, climax takes many hundreds of years to develop. Secondary successions, for example in clearings, proceed much faster. Still, it takes at least 200 years for the forest to recover in a moderate, humid climate.
If the climate is particularly harsh (as in the desert, tundra or steppe), the duration of the episodes is shorter, since the community cannot significantly change the unfavorable physical environment. Secondary succession in the steppe, for example, lasts about 50 years.
The main stages of secondary succession in temperate climates:
· the first stage of herbaceous vegetation lasts about 10 years;
· second stage of bushes? from 10 to 25 years;
· third stage of deciduous trees? from 25 to 100 years;
· fourth stage of coniferous trees? more than 100 years.
Successions can be of different scales. They can go slowly, over thousands of years, or quickly, over several days.
The duration of succession is largely determined by the structure of the community.
During primary succession, it takes many hundreds of years for the development of a stable community.
Pay attention!
The need to destroy the parent rock is the main reason for the slow progress of primary successions.
Secondary successions proceed much faster. This is explained by the fact that the primary community leaves behind a sufficient amount of nutrients and developed soil, which creates 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 off and smoothed the soil cover, crushed rocks. With its retreat and climate warming, vast expanses of bare, lifeless land were exposed. Gradually it was populated by various plants and animals. Of course, these changes happened very slowly. Where the glacier destroyed tropical forests, their restoration continues to this day. These areas have not yet reached a steady state. So they didn’t have enough millions of years to complete succession.
The changes that led to broad-leaved forests also came slowly. Miocene (20 million years ago) to the current northern Central Asian deserts.
Succession occurs much faster after a forest fire, when in a certain sequence one biocenosis is replaced by another, which finally leads to the restoration of a stable community.
Fouling of exposed cliffs occurs relatively quickly: 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 an infusion of hay.
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 predicted.
Succession is the result of changes that the communities themselves make to the habitat, 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, consequently, the most numerous connections between organisms.
Thus, the climax biocenosis is maximally protected from possible disturbances from external factors and is in a state of equilibrium.
The main feature of ecological succession is that changes in the community always occur towards an equilibrium state.
When an ecosystem approaches its final stable state (climax state), in it, as in all equilibrium systems, all development processes slow down.
Observations of succession show that some certain properties of biocenoses change in one direction, whatever the type of succession.
Let's formulate them.
Species of plants and animals are constantly changing.
The species diversity of organisms increases.
The size of organisms increases during succession.
Linear food chains dominated by herbivores evolve into complex food webs. Detritivorous forms (consumers of dead organic matter) begin to play an increasingly important role in them.
Biological cycles are lengthening and becoming more complex, organisms are becoming more and more ecologically specialized.
The biomass of organic matter increases. There is a decrease in the net production of the community and an increase in respiration rate.
1.5 The meaning of succession
A mature community, with its greater diversity, richness of organisms, more developed trophic structure, and 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 a young community. However, a young community is capable of producing new biomass in much larger quantities than the old one. The remains of civilizations and deserts, the emergence of which is due to human activity, are excellent proof that man has never realized his close connection with nature, the need to adapt to natural processes, and not to command them. Nevertheless, even the knowledge that has been accumulated at present is sufficient to ensure that the transformation of our biosphere into one vast carpet of arable land is fraught with enormous danger. For our own protection, certain landscapes must be introduced to natural communities.
Thus, a person can reap a rich harvest in the form of pure products, artificially maintaining the community in the early stages of succession. Indeed, in a mature community, which is at the climax stage, the net annual production is spent mainly on the respiration of plants and animals and may even be equal to zero.
On the other hand, from a human point of view, the resilience of a community in the climax stage, its ability to withstand the effects of physical factors (and even manage them) is a very important and highly desirable property. A person is interested in both productivity and stability of the community. To support human life, a balanced set of both early and mature stages of succession, which are in a state of exchange of energy and matter, is necessary. The excess food created in young communities allows the maintenance of older stages that help withstand external influences.
Arable lands, for example, should be considered young successional stages. They are maintained in this condition thanks to the continuous labor of the farmer. Forests, on the other hand, are older, more diverse and more stable communities with low net production. It is extremely important that people give equal attention to both types of ecosystems. If a forest is destroyed in pursuit of temporary income from timber, water supplies will decrease and soil will be swept away from the slopes. This will reduce the productivity of the areas. Forests are valuable to humans not only as suppliers of wood or a source of additional areas that can be occupied by cultivated plants.
Unfortunately, people have little awareness of the consequences of environmental violations that occur in the pursuit of economic gain. This is partly due to the fact that even environmental specialists cannot yet make accurate predictions of the consequences that various disturbances of mature ecosystems lead to. The remains of civilizations and deserts, the emergence of which is due to human activity, are excellent proof that man has never realized his close connection with nature, the need to adapt to natural processes, and not to command them.
Nevertheless, even the knowledge that has been accumulated at present is sufficient to ensure that the transformation of our biosphere into one vast carpet of arable land is fraught with enormous danger. For our own protection, certain landscapes must be represented by natural communities
ATTACHMENT:
Indicate the stages of overgrowing of a reservoir from the proposed vegetation: sphagnum, sedge, marsh pine, mixed forest, wild rosemary (sedge, sphagnum, wild rosemary, marsh pine, mixed forest).
Distribute the stages of succession in the correct order: annual plants, shrubs, deciduous trees, perennials, coniferous trees (annuals, perennials, shrubs, deciduous trees, coniferous trees)
Arrange the ongoing stages of succession in time: colonization of the territory by mosses. germination of herbaceous plant seeds, colonization by shrubs, formation of a stable community, colonization of bare rocks by lichens
1. colonization of bare rocks by lichens
2. colonization of the territory with mosses
3. germination of herbaceous plant seeds
4. colonization by shrubs
5. building a sustainable community
The course of evolution (development) of a community cannot be predicted.
The most general patterns of evolution of biocenoses:
1.The types of plants and animals during the development of a community can be predicted
2.Lowers diversity of species of organisms.
3. Sizes of organisms during succession are decreasing.
4, Food chains shortened and simplified. They are beginning to play an increasingly important role detritivores.
5.Biological cycles become more complicated , organisms become increasingly ecologically specialized.
6. Biomass of organic matter during community development increases. Happening height clean community products and slowdown breathing intensity.
Ecological succession
One of the main achievements of ecology was the discovery that not only organisms and species develop, but also ecosystems. Communities are constantly changing. Some organisms die, others come to replace them. Energy and nutrients flow through the community in an endless stream.
Concept and types, 2018.
The sequence of changes in communities (ecosystems, biocenoses) on the same territory called succession.
There are three points to consider when defining ecological succession.
Firstly, succession occurs under the influence of the community, i.e. biotic component of the ecosystem.
Secondly, succession is directed in a certain way and can be predicted (anticipated).
The third aspect is that the culmination of succession is the emergence of a stabilized ecosystem in which per unit energy flow there is a maximum biomass and a maximum number of interspecific interactions.
The final stage of succession is called menopause community.
Traditionally, the process of succession is illustrated by the example of the overgrowing of a small reservoir in a forest (Fig. 34). The above-water parts of plants of coastal herbaceous vegetation die off annually, due to which the area of the clean water surface of the pond decreases.
Gradually, conditions favorable for the development of more powerful coastal plant species, such as willow, are formed near the shores. Taking root, the willow begins to pump water out of the pond, drying up the area of its existence. As a result, willow is replaced by small-leaved tree species: birch, hazel.
Concept and types, 2018.
The surface area of the pond continues to decrease, soil moisture decreases, and forest soil begins to form. Small-leaved trees are replaced by broad-leaved ones, oaks and lindens gradually appear, and various shrubs and herbaceous plants develop under their crowns. Conditions are gradually being created for the introduction of coniferous trees into communities. As a result of the excessive intake of biogenic chemical elements, mainly nitrogen and phosphorus, into the reservoir along with organic matter, a “blooming” of water occurs: unicellular algae multiply in huge quantities. There is an “aging” of lake ecosystems – their eutrophication.
Dying algae, along with foraminifera, fall “as rain” to the bottom, which leads to a decrease in the depth of the pond. As a result, a forest is formed in place of the reservoir, which is virtually no different from the one that surrounded the reservoir several decades ago. Under certain external conditions, the lake turns into a peat bog, which is a stable climax-type ecosystem.
There are a very large number of classifications of successions.
Depending on the reasons for succession, they distinguish
· exodynamically e (from the Greek word exo - outside) successions caused by factors external to a given ecosystem,
· endodynamic(from the Greek word endon - within) succession caused by internal mechanisms of the ecosystem
Exodynamic successions can be caused by climate changes, lowering groundwater levels, rising sea levels, etc. Such changes can last for centuries and millennia. They are associated mainly with the action of mechanisms of adaptation of the ecosystem to environmental factors, which in turn are based on the mechanisms of adaptation of living organisms in the ecosystem.
Endodynamic Succession is driven by special laws, the mechanisms of which are still largely unclear. It is known that on any, even absolutely lifeless, substrate such as sand dunes or hardened lava, sooner or later life blossoms. Moreover, forms of life, or more precisely, types of communities, successively replace each other in a given space, gradually becoming more complex and increasing species diversity, forming a so-called successional series, consisting of successive stages marking the replacement of one community by another.
The succession series ends at the maturity stage, at which the ecosystem changes very little. Ecosystems at this stage are called menopausal(from the Greek word klimax - ladder).
The duration of succession from the origin of an ecosystem to the climax stage can be up to hundreds and even thousands of years. Such a long duration is mainly due to the need to accumulate nutrients in the substrate.
There is another type of classification of successions.
It is necessary to distinguish autotrophic and heterotrophic successions. All autotrophic successions occur in ecosystems where the central link is vegetation (phytocenosis).
The dynamics of heterotrophs are entirely subordinate to the dynamics of autotrophs - the change of animal communities depends on the change of plant communities. Autotrophic successions can theoretically last forever, since they are constantly fed by the energy of the Sun.
IN heterotrophic successions Only animals (heterotrophs, consumers) participate. Dead plants can also be involved in this process, for example, fallen trees, stumps, etc., which are, as a rule, a source of energy for heterotrophic succession.
Heterotrophic succession presupposes the obligatory presence of a certain supply of energy accumulated in organic matter. It ends when the energy resource is exhausted, that is, after complete decomposition of the original substrate. After this, the ecosystem ceases to exist. Thus, the concept of menopause is not defined for her. Unlike biogeocenoses, such ecosystems are mortal.
Examples of heterotrophic succession are changes in communities on the corpse of an animal (changes occur approximately in this order: bacteria - ants - carrion beetles, carpet beetles, lice beetles); on a pile of manure (or droppings); on the fruit left lying on the ground - an apple, for example.
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The longest heterotrophic succession is observed on the trunk of a large fallen tree.
Thus, in In heterotrophic succession there is no climax stage.
Heterotrophic succession is well associated with fossil fuel-dependent societies. The dynamics of heterotrophic succession are described by a curve with a rapid increase in the number of organisms until a certain maximum is reached, then the number of organisms gradually decreases as the energy resource is exhausted. It is not possible to achieve any stable state (climax). Such a society is rapidly progressing, but nevertheless it is initially doomed to extinction.
We have already “skimmed the cream” from most of the deposits. Their further operation will require increasingly greater energy investments over time. Therefore, the efficiency of mining will steadily decline. Along with this, the viability of a civilization built on heterotrophic succession will also decline, unless, of course, catastrophic changes occur even earlier. That is why we are devoting a huge amount of effort to finding new sources of energy. But even if we learn to control thermonuclear fusion, it will not change our destructive nature.
Depending on the initial conditions, succession is divided into
- primary(when organisms colonize empty areas that have never been inhabited before) and
- secondary(the process takes place in places that were already inhabited, but lost their inhabitants as a result, for example, of glaciation or human activity).
Primary succession- the process of development and change of ecosystems in previously uninhabited areas, beginning with their colonization.
A classic example of primary succession is the development of a community on cooled lava or ash in the zone of action of a volcano, on rocks and stones. Initially, lichens appear, enriching the surface with nitrogen.
Concept and types, 2018.
After some time, mosses begin to develop in the biotope. After this, grass grows along with mosses, then small-leaved trees. It is not difficult to notice that all this time the soil is developing in the ecosystem, making it possible for the growth of increasingly complex organisms.
Secondary succession occurs where a biocenosis previously existed, but it was destroyed as a result of natural or anthropogenic factors.
For example, secondary succession begins in places of deforestation, on abandoned arable land, in abandoned villages, after natural disasters: floods, tsunamis, forest windfalls, earthquakes. The study of pyrogenic (arising as a result of fires) successions is of particular importance, since with the development of human society, the proportion of fires caused by humans increases.
Secondary succession ends with a stable community stage in 150–250 years, and primary lasts about 1000 years.
4.2.1 Climax ecosystem.
Succession ends with a stage when all species of the ecosystem, while reproducing, maintain a relatively constant number and no further change in its composition occurs. This equilibrium state is called climax, and the ecosystem is called climax. Under different abiotic conditions, different climax ecosystems are formed. In a hot and humid climate it will be a tropical rain forest, in a dry and hot climate it will be a desert. The main biomes of the earth are the climax ecosystems of the corresponding geographical areas.
The spruce forest is the last climax stage of ecosystem development in the climatic conditions of the North, i.e., it is already an indigenous biocenosis (Fig. 33).
Rice. 33. Successive successions during the formation of a spruce forest.
Initially, so-called pioneer species, such as lichens and encrusting algae, settle on the lifeless substrate). Over 5-10 years, they somewhat enrich the substrate with nutrients, forming the beginnings of soil. Then grasses settle on these still very poor soils, further enriching the soil. About 15 years from the beginning of succession, the first shrubs settle in the once lifeless space, which are gradually replaced by deciduous light-loving trees, most often birch and aspen, which are characterized by rapid growth.
Concept and types, 2018.
By the age of 50, the strongest trees stand out in the young deciduous forest, which shade the weaker shoots, which die, making it possible for spruce to settle under the canopy of the deciduous forest. Spruce is more shade-tolerant; under the protection of deciduous trees, it gradually catches up with them in growth, winning their living space. Around the age of 70, the ecosystem reaches the stage of mixed spruce-deciduous forest. By that time, deciduous trees have time to grow old, and gradually the spruce reaches the first tier, shading and thinning out all deciduous vegetation. By the age of 90, this ecosystem reaches the climax stage, which is characterized by the almost complete absence of deciduous trees; spruce becomes the dominant edificatory species, forming in a special way the entire life of the community inhabiting this ecosystem.
The law of thermodynamics is called the law of conservation of the structure of the biosphere).
Ecological succession - concept and types. Classification and features of the category "Ecological succession" 2017-2018.
