1. Continue the definition: “An ecosystem is...” Options:
1) a collection of different populations that persist indefinitely and interact with each other and environment
2) relationships between species within the biocenosis
3) a set of individuals living in the same territory
2. Large terrestrial ecosystems, which include smaller ecosystems connected to each other, are called:
1) biocenoses
2) biotopes
3) successions
4) biomes
3. Gross primary production of an ecosystem is called:
1) the total amount of matter and energy supplied from autotrophs to heterotrophs
2) the total amount of matter and energy produced by autotrophs
4. Primary production in ecosystems is formed by:
1) producers 3) detritivores
2) consumers 4) decomposers
5. Secondary products in ecosystems are formed:
3) detritivores
4) decomposers
1) producers
2) consumers
3. The lowest productivity is typical for ecosystems:
4) deserts
7. The greatest productivity is typical for ecosystems:
1)tropical rain forests
2) central parts of the ocean
3) hot deserts
4) temperate forests
8. Establish the sequence in which ecosystems should be located, taking into account the increase in their productivity:
1) central parts of the ocean
3) mountain forests
2) temperate forests
4) coral reefs
1, 3, 2, 4
9. Rank the following ecosystems in order of increasing productivity:
1) moist forests 3) steppes
2) oak groves 4) arctic tundra
4, 2, 3, 1
10. Despite the fact that the ocean occupies 71% of the area of our planet, its production is 3 times less than the production of land plants. Accordingly, the biomass of algae is 10 thousand times less than the biomass of land plants. How can we explain this?
(The main producers of land are trees, and the main producers of the ocean are small unicellular algae; different growth; herbivorous consumers of the ocean quickly eat the producers, and the supply of algae constantly remains low, but on land it’s the other way around)
11. List the principles of functioning of ecosystems.
(Obtaining resources and getting rid of waste within the cycle of all elements; existence due to the practically inexhaustible and clean solar energy; correspondence of the population biomass to the trophic level occupied by it)
12. Describe the phenomena indicating human violation of the principles of functioning of ecosystems.
(Disruption of the cycle of substances (pollution, acid rain); the ecosystem functions not only due to solar energy, but also wind energy, firewood, fossil fuels and other sources; the principle is violated - at the end of long food chains there cannot be large biomass. Man is the third trophic level, i.e. it eats meat. So that all people can eat meat, it is necessary to expand the cultivated area by 10 times.)
13. Atmospheric nitrogen is included in the cycle of substances due to the activities:
1) chemosynthetic bacteria
2) denitrifying bacteria
3) nitrogen-fixing bacteria
4) nitrate bacteria
14. Sulfur in the form of hydrogen sulfide enters the atmosphere due to the activities of:
1) denitrifying bacteria
2) sulfobacteria
3) methylotrophic bacteria
4) sulfur bacteria
15. Nitrogen enters plants during the cycle of substances in the form of:
1) nitric oxide 3) nitrates
2) ammonia 4) nitric acid
16. The main anthropogenic sources of sulfur entering the large cycle of substances are:
1) thermal power plants
2) fertilizers
3) tests atomic weapons
4) aircraft flights
17. The cycle of chemical elements between organisms and the environment is called:
1) energy cycle
2) biogeochemical cycle
3) the cycle of living organisms
4) nitrogen cycle
18. Determine which cycle (nitrogen, sulfur cycle) each characteristic (1-6) corresponds to. Establish a correspondence between the cycle of substances and their characteristics:
A, B, A, B, B, A
19. In a terrestrial biocenosis, microorganisms and fungi complete the decomposition of organic compounds into simple mineral components, which are again involved in the cycle of substances by representatives of a certain group of organisms. Name this group:
1) consumers of the 1st order
3) producers
2) consumers of the 2nd order
4) decomposers
20. Carbon enters the cycle of substances in the biosphere in the composition of:
1) carbon dioxide 3) limestone
2) free carbon
21. Carbon leaves the cycle of substances (forming sedimentary rocks) in the composition:
1) calcium sulfate 3) calcium nitrate
2) calcium carbonate
4) calcium sulfide
22. The complete oxygen cycle in nature lasts about:
2) 2000 years
3) 1 million years
4) 100 million years
23. The complete water cycle in nature lasts about:
3) 1 million years
4) 100 million years
24. The rule of edge (border) effect states: at the junctions of biocenoses, the number of species in them:
1) does not change
3) decreases
2) increases
4) does not increase significantly
25. The body mass of living organisms in an ecosystem is called:
1) bioproducts
3) biomass
2) bioenergy 4) bionumber
26. Seasonal periodicity in nature is most pronounced:
1) in the subtropics
3) in temperate latitudes
2) in deserts 4) in the tropics
27. The frequency of opening and closing of oyster shells is referred to as rhythms:
1) daily 3) annual
2) tidal
4) seasonal
28. Leaf fall is classified as a rhythm:
1) lunar 3) seasonal
2) daily 4) annual
29. The time-consistent replacement of one community by another in a certain area of the environment is called:
1) succession 3) menopause
2) fluctuation 4) integration
30. Among the listed examples of primary succession are:
1) transformation of abandoned fields into broad-leaved forests
2) gradual replacement of clearings by deciduous forests
3) gradual overgrowth of bare rock with lichens
4) transformation of fires into spruce forests
31. Among the listed succession processes, primary succession includes:
1) transformation of burned areas into spruce forests
2) gradual replacement of clearings by pine forests
3) transformation of degraded pastures into oak forests
4) the appearance of a pine forest on the shifting sands
32. Among the listed succession processes, secondary succession is considered:
1) turning abandoned fields into oak forests
2) the appearance of lichens on cooled volcanic lava
3) gradual fouling of bare rock
4) the appearance of a pine forest on the shifting sands
33. The main reason for the instability of ecosystems is (are):
1) unfavourable conditions environment
2) lack of food resources
3) imbalance in the circulation of substances
4) excess of certain species
34. A relatively stable state of an ecosystem, in which balance is maintained between organisms, as well as between them and the environment, is called:
1) menopause 3) fluctuation
2) succession 4) integration
35. In which ecosystem (A, B) does each of the listed (1-6) species grow?
A, 2-B, 3-B, 4-B, 5-A, 6-A
36. Eutrophication of water bodies is considered:
1) enrichment of water bodies with nutrients that stimulate the growth of phytoplankton
2) the process of turning a swamp into a lake
3) the process of enriching water with oxygen
Topic 7. Biosphere
1. The shell of the Earth, containing the entire totality of living organisms and that part of the planet’s substance that is in continuous exchange with these organisms, is called:
1) atmosphere 3) ecosphere
2) hydrosphere 4) biosphere
2. Which of the following is not included (in whole or in part) in the biosphere:
1) atmosphere 4) lithosphere
2) magnetosphere 5) asthenosphere
3) hydrosphere 6) ionosphere
3. At what height is the so-called separate ozone layer:
1) 20-30 km above sea level
2) 10 15 km above sea level
3) 25-50 km above sea level
4) there is no separate ozone layer
4. The main role of the ozone layer (screen) is:
1) in protection from ultraviolet radiation
2) in maintaining the planet’s climate
3) in creating the greenhouse effect
5. Indicate three substances whose content in the earth’s crust is maximum:
1) hydrogen
2) aluminum
3) oxygen
4) calcium
5) silicon
6. Distinctive features of the oceanic crust (compared to continental crust):
1) thickness 3-7 km
2) thickness 20-40 km
3) granite layer is present
4) there is no granite layer
5) sedimentary layer on average less than 1 km
6) sedimentary layer on average 3-5 km
7) second layer between sedimentary and basalt layers
7. Rocks that cover more than 76% of the surface of the continents are rocks:
1) igneous
2) sedimentary
3) metamorphic
8. Characterize the layers of the Earth that make up the biosphere.
(Atmosphere(the gas envelope of the Earth) consists of a mixture of gases: nitrogen, oxygen and inert gases. Its lower layer, up to 15 km, is called the troposphere. At an altitude of 15-35 km from the Earth’s surface there is an “ozone screen”.
Hydrosphere(water shell of the Earth) makes up 70% of the Earth's surface. The largest reserves of water are concentrated in the World Ocean (about 90%). The state of the hydrosphere determines climatic conditions.
Lithosphere(solid shell of the Earth) includes the earth's crust and the upper part of the mantle. Life in the lithosphere is concentrated in its upper, fertile layer - the soil.)
9. List the main features of the biosphere that distinguish it from other shells of the Earth.
(Within the biosphere, the geological activity of all living organisms is manifested.
Continuous circulation of substances, regulated by the activities of living organisms.
The biosphere receives energy from the Sun and is therefore an open system.)
10. List the main functions of the biosphere and describe them.
(Gaseous function is the release and absorption of gases by living organisms.
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. Changes them species composition, the number of certain organisms, trophic structure and other indicators of the community.
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.
main feature This process is that community changes always occur in the direction of an equilibrium state.
1.1 Types of successions
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 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 competition, plants 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; V 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 economic activity people do not interfere in the relationships between organisms, a climax community develops, which can exist indefinitely - 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 it becomes difficult for the seedlings of the species that first entered the field 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 perennials herbaceous plants family Poaceae, or Poagrass
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 temperate conditions to humid climate the forest was able to recover.
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 climate:
· 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 rainforests, 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 one biocenosis is replaced by another in a certain sequence, 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 view 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 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. However, even the knowledge that has been accumulated at present is sufficient to be confident that the transformation of our biosphere into one vast carpet of arable land is fraught with great 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 in the right order: annual plants, shrubs, deciduous trees, perennials, coniferous trees(annuals, perennials, shrubs, deciduous trees, conifers)
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.
Although the biocenosis is a rather conservative natural system, under the pressure of external circumstances it can give way to another biocenosis. The successive change over time of some communities by others in a certain area of the environment is called succession (from Lat. successia succession, inheritance). As a result of succession, one community is successively replaced by another without returning to the original state. Succession is caused by the interaction of organisms, mainly wounds, with each other and with the environment.
Successions are divided into primary and historical. Primary ones occur on primary soil-free Soils - volcanic tuff and lava fields, loose sand, rocky placers, etc. As the phytocenosis develops from the pioneer stage to the saturated one, the soil becomes more fertile and more and more chemical elements are involved in the biological cycle in increasing quantities. As fertility increases, plant species that grow in nutrient-rich soils displace species that are less demanding in this regard. At the same time, the animal population is changing. Secondary successions take place in the habitats of destroyed communities, where soils and some living organisms are preserved. The destruction of biocenoses can be caused by spontaneous natural processes (hurricanes, rainstorms, floods, landslides, prolonged droughts, volcanic eruptions, etc.). as well as changes in the habitat by Organisms (for example, when a reservoir becomes overgrown water environment replaced by peat deposits). Secondary successions are typical for degraded pastures, burnt areas, deforestation, arable lands and other lands excluded from agricultural use. as well as for artificial forest plantations. For example, often under the canopy of middle-aged pine crops on a su sandy soils Abundant natural regeneration of spruce begins, which will eventually displace pine, provided that regular clear-cutting of the pine stand and silvicultural work are not carried out. In burnt areas with sandy loam and loamy soils, pioneer vegetation of fireweed and warty birch is eventually replaced by spruce plantations.
In recent decades, large-scale drainage and irrigation works have acquired particular importance in changing vegetation cover. In swamp forests that find themselves in the zone of influence of drainage canals, hygrophyte plants disappear (sedge alders, for example, transform into nettles). The transformation of species composition, including animal populations, also affects forest areas that migrate to drained swamps. Irrigation reclamation, on the contrary, promotes the active penetration of plants of hygrophilic and mesophilic groups into waterlogged areas as a result of the accumulation of water used for irrigation. Industrial pollution also has a noticeable impact on biocenoses. All these changes are secondary successions.
The replacement of one biocenosis by another during succession forms a succession series, or series. The study of successional series has great importance due to the increasing anthropogenic influence on biocenoses. The end result of this kind of research may be the prediction of the formation of natural-anthropogenic landscapes. The study of secondary successions and the factors that cause them plays an important role in solving problems of protection and rational use of biological and land resources.
If natural course succession is not disturbed, the community gradually comes to a relatively stable state in which balance is maintained between organisms, as well as between them and the environment - to climax. Without human intervention, this biocenosis can exist indefinitely, for example, blueberry pine forest, lichen tundra on sandy soils.
The concept of menopause was developed in detail by the American botanist H. Cowles and is widely used in foreign botanical and geographical literature. According to this concept, climax is the terminal stage of community evolution, which corresponds to a certain type of soil - pedoclimax. Successions leading to this stage are called progressive, and successions that remove the biocenosis from it are called regressive. However, one cannot attach an absolute meaning to the concept of “climax” and assume that when it is reached, the community stops development.
Biocenoses that, being disturbed, return to their original state are called indigenous. In place of the felling of a blueberry pine forest or an oxalis spruce forest, a birch forest will grow, and it, in turn, will again be replaced by a blueberry pine forest or an oxalis spruce forest. In this case we're talking about about indigenous forest types.
Transformed biocenoses do not return to their original state. Thus, a low-lying sedge bog, drained and developed for crops, develops towards the formation of birch or alder small forests after the peat deposit has been drained and the reclamation network has been destroyed and agricultural use has ceased for some reason. The zoocenosis of this small forest differs from the community of animal species of the open grass swamp.
1.6 Classification
For the purpose of scientific knowledge of biocenoses and the practical application of knowledge about them, communities of organisms must be classified according to their relative size and complexity of organization.
The classification is intended to put in order all their diversity using a system of taxonomic categories, i.e. taxa, which in this case unite groups of biocenoses with varying degrees of commonality of individual properties and characteristics, as well as structure and origin. At the same time, a certain subordination of taxa that are simple in content to complex ones, taxa of small (local) dimension to taxa of planetary dimension, and a gradual complication of their organization must be observed. In addition, when classifying biocenoses, the presence of possible boundaries between them should be taken into account.
There are no particular difficulties in establishing boundaries when neighboring biocenoses have clear indicator features. For example, a raised bog with wild rosemary and moss cover and a low-growing pine stand contrasts with the surrounding pine forest community on sandy soils. The border between forest and meadow is also clearly visible. However, since the conditions of existence of communities change more gradually than the communities themselves, the boundaries of biocenoses are usually blurred. The gradual transition from one phytocenosis to another with their proximity and the replacement of one phytocenosis by another in time is reflected in the concept of continuum (from the Latin continuum - continuous) of vegetation, developed by the Soviet geobotanist L. G. Ramensky and the American ecologist P. H. Whittaker.
The boundaries between communities appear more sharply in cases where edificators have the greatest transformative effect on the environment, for example, the boundaries between forests formed by different tree species - pine, spruce, oak and others. In steppes, semi-deserts and deserts, the boundaries between communities are more gradual, since the environment-transforming role of herbaceous species is less contrasting.
The classification of communities uses taxonomic categories accepted in plant geography and based on the identification of dominants and edificators, which indicates the recognition of phytocenosis as an ecological framework that determines the structure of the biocenosis. The taxonomic system of communities built on the basis of dominants and edifiers can be expressed in the following series: association - group of associations formation group of formations class of formations biome type - biocenotic cover.
The lowest taxonomic category is association. It is a set of homogeneous microbiocenoses with the same structure, species composition and similar relationships both between organisms and between them and the environment. In field conditions, the main signs of its identification are: the same layer structure, similar mosaic (spotted, scattered), coincidence of dominants and edificators, as well as relative homogeneity of the habitat. The name of the association for multi-tiered communities consists of the generic names of the dominant tier (condominant) and edificators in each tier, for example, juniper-mossy pine forest, birch-blueberry spruce forest, etc. The name of complex meadow associations is formed by listing dominants and subdominants, with the dominant being called the latter , for example, caustic-meadow-poagrass association. Usually meadow associations are indicated by Latin: Ranunculus + Poa pratensis.
A group of biocenotic associations is formed by associations that differ in the composition of one of the tiers. Blueberry pine forest, for example, shares associations with an understory layer of juniper, buckthorn and birch undergrowth. The group of cereal–sedge–forb associations includes meadow communities with a set of named groups of meadow grasses (grasses, small sedges, forbs).
A biocenotic formation includes groups of associations. The formation is distinguished by its dominant, by which it is called: the formation of Scots pine, black alder, pedunculate oak, white saxaul, ranunculus, wormwood, etc. This is the basic unit of middle rank, widely used in mapping forest vegetation.
The emergence of a biocenosis begins with the appearance of the first organisms in areas devoid of life (lava flows, volcanic islands, screes, exposed rocks, sand deposits and dried bottoms of reservoirs). Settlement begins with the accidental introduction of organisms from territories they have already developed and depends on the properties of the substrate. This area may not be suitable for propagation for many plant seeds and invading animals. Often, especially in humid zones, the first settlers are representatives of algae, mosses and lichens.
As a rule, only a few of the introduced ones develop successfully plant species. Animals-consumers settle somewhat later, since their existence without food is impossible, but their occasional visits to areas being developed are quite common occurrence. This stage of development of the biocenosis is called pioneer. Although at this stage the community has not yet formed, it already has an impact on the abiotic environment: soil begins to form.
The pioneer stage gives way to the unsaturated stage, when plants begin to regenerate (by seeds or vegetatively) and animals begin to reproduce. In an unsaturated biocenosis, not all ecological niches are occupied.
Gradually, the rate of settlement of the site increases due to both an increase in the number of individuals of pioneer vegetation before the formation of thickets, and the introduction of new species. The species composition of such a community is still unstable; new species are introduced quite easily, although competition begins to play a noticeable role. This stage of development of a biocenosis is a grouping.
With the subsequent development of the community, the vegetation cover becomes differentiated into tiers and synusias, and its mosaic nature, species composition, food chains and consortia become stable. Ultimately, all ecological niches are occupied and further introduction of organisms becomes possible only after the old residents are displaced or destroyed. This final stage of biocenosis formation is called saturated. However, the further development of the biocenosis does not stop and random deviations in the species composition and relationships both between organisms and with the environment may still occur.
Random deviations in the structure of the biocenosis are called fluctuations. As a rule, they are caused by random or seasonal changes in the number of species included in the biocenosis as a result of adverse meteorological phenomena, floods, earthquakes, etc.
Although the biocenosis is a rather conservative natural system, under the pressure of external circumstances it can give way to another biocenosis. The successive change over time of some communities by others in a certain area of the environment is called succession. As a result of succession, one community is successively replaced by another without returning to the original state. Succession is caused by the interaction of organisms, mainly wounds, with each other and with the environment.
Successions are divided into primary and historical. Primary ones occur on primary soil-free soils - volcanic tuff and lava fields, loose sand, rocky placers, etc. As the phytocenosis develops from the pioneer stage to the saturated one, the soil becomes more fertile and more and more chemical elements are involved in the biological cycle in increasing quantities. As fertility increases, plant species that grow in nutrient-rich soils displace species that are less demanding in this regard. At the same time, the animal population is changing. Secondary successions take place in the habitats of destroyed communities, where soils and some living organisms are preserved. Secondary successions are typical for degraded pastures, burnt areas, deforestation, arable lands and other lands excluded from agricultural use. as well as for artificial forest plantations. For example, often under the canopy of middle-aged pine crops on sandy loam soils, abundant natural regeneration of spruce begins, which will eventually displace pine, provided that regular clear-cutting of the pine stand and silvicultural work are not carried out.
The replacement of one biocenosis by another during succession forms a succession series, or series. The study of succession series is of great importance due to the increasing anthropogenic influence on biocenoses. The end result of this kind of research can be the prediction of the formation of natural and anthropogenic landscapes. The study of secondary successions and the factors that cause them plays an important role in solving problems of protection and rational use of biological and land resources.
If the natural course of succession is not disturbed, the community gradually comes to a relatively stable state in which balance is maintained between organisms, as well as between them and the environment - to climax. Without human intervention, this biocenosis can exist indefinitely, for example, blueberry pine forest, lichen tundra on sandy soils.
The concept of menopause was developed in detail by the American botanist H. Cowles and is widely used in foreign botanical and geographical literature. According to this concept, climax is the terminal stage of the evolution of a community, which corresponds to a certain type of soil - pedoclimax. Successions leading to this stage are called progressive, and successions that remove the biocenosis from it are called regressive.
Biocenoses that, being disturbed, return to their original state are called indigenous.
Transformed biocenoses do not return to their original state.
No community exists forever; sooner or later it is replaced by another community. This occurs under the influence of external causes or as a result of changes in the environment due to the vital activity of organisms forming biocenoses, including the introduction of new species into communities. Among the diverse forms of bold communities, primary and secondary successions are distinguished. Primary successions represent a natural change of communities in areas not occupied by vegetation, for example, on sandbanks in river floodplains, in places freed up after the retreat of glaciers, etc. Depending on the substrate (its physical and chemical properties) here, at first, either only bacteria, algae and lichens, or along with them, vascular plants settle. [...]
Such changes in communities are called succession. In the process of primary successions, the natural communities, and soil.[...]
The described change of communities occurs over 60-80 years. The stability of such communities is determined by a number of reasons: firstly, the composition of the community by plants with strong environment-forming properties, which limit the possibility of new species introducing into it. At the same time, the conditions for the renewal of the species that make up the community are sufficient. Second, resilient ecosystems have a well-balanced, diverse range of animal species. The interactions of populations in such communities are diverse and well adapted to living together. There are virtually no opportunities for the introduction of new species. All these properties of a stable community ensure its long existence.[...]
Classic example changes in communities under the influence of the vital activity of organisms is a process of overgrowing of lakes. The water of any lake, especially if it is rich in nitrogen and ash elements, is home to a huge number of microscopic organisms (algae, protozoa, etc.). When they die, they fall to the bottom along with fine earth brought into the lake from the slopes. This process, repeating from year to year, leads to the formation of sapropel at the bottom of the lake, to a decrease in the depth of the lake, to the penetration sunlight to the bottom of the lake. As a result, conditions are created for the settlement of mosses and multicellular algae, which accelerates the accumulation of organic residues (sapropelic peat) at the bottom of the lake and leads to even greater shallowing of the reservoir. And this is accompanied by the settlement of vascular plants with shoots immersed in water or with leaves floating on the surface of the water (pondweed, water lilies, egg capsules, etc.). The next stage of lake overgrowth is the settlement of lake reeds and common reed, developing a huge mass of above-ground shoots, from which, after they die, reed or reed peat is formed. As the lake continues to fill with dead plant remains and becomes shallower, sedges colonize. The lake is gradually turning into a swamp. By observing individual belts of aquatic vegetation on an overgrowing lake, it is possible to restore the main stages of its overgrowth - transformation into a swamp.[...]
In a similar way, communities change on glacial deposits in the form of very thin, nutrient-poor soil. Observations in Alaska showed that the formation of a phytocenosis begins with mosses and sedges; after them, creeping and then shrubby forms of willows are included in the community. Later (after about 20-25 years) olipatniks appear; after them spruce appears, which forms the basis of the final community in the form of a mixed forest, which forms approximately 100 years after the start of succession.[...]
Progressive changes in the community lead to the replacement of one community by another. The reason for such changes could be factors that have been acting in one direction for a long time, for example, increasing drying out of swamps as a result of reclamation, increasing anthropogenic pollution of water bodies, and increased grazing of livestock. The resulting replacement of one biocenosis by another is called exogenetic. If at the same time the structure of the community is simplified, the species composition is depleted, and productivity decreases, then such a change in the community is called digression. However, the replacement of one biocenosis by another can occur as a result of processes occurring within the community itself, as a result of the interaction of living organisms with each other.[...]
This is a specific form of community change, consisting in the consistent use various types decaying organic matter. The peculiarity of such successions is that communities consist only of heterotrophic organisms, and the course of successions is directed towards increasing structural and chemical simplification of accumulations of organic matter.[...]
So, succession is a natural, consistent change of communities in ecosystems, caused by the influence of a complex of internal and external factors. Change over time is a natural property of ecological communities. The influence of a complex of factors causes succession in ecosystems as an adaptive response. F. Clements believed that succession ends with the formation of a community most adapted to the complex climatic conditions, which he called “climax formation” or simply “climax”; Currently, this formation is considered a temporary state: in the process of secular changes in conditions (climate and other environmental factors), full-scale changes in ecosystems occur. There are progressive successions, in which species diversity gradually increases, but there are also digressions - regressive successions aimed at uniting and simplifying communities. The latter began to manifest itself especially often in the presence of large-scale adapted impacts on biocenoses that violate optimal conditions.[...]
The development of biocenoses, in which one community is replaced over time by another, is called ecological succession1. In most cases, succession processes occupy time intervals measured in years and decades, although in some cases changes in communities occur at a faster rate (for example, in temporary reservoirs). Along with this, secular changes in ecosystems are known, reflecting the general paths of evolution of the biosphere.[...]
To evaluate these measures of diversity, Wilson and Schmida chose four criteria: number of community turnovers, additivity, independence from alpha diversity, and independence from excessive sample size. The extent to which each index measures species turnover was assessed by calculating -diversity for two hypothetical gradients, one of which is homogeneous (i.e.[...]
When vegetation is destroyed without changing soil and ground conditions, communities change in the direction of returning to the state characterizing the original root type. For example, when destroyed coniferous forests in clearings or burnt areas, grasses (reed grass, fireweed, etc.) first grow, and then plantations of small-leaved species (birch, aspen) are gradually formed, under the canopy of which spruce or other conifers settle, which subsequently emerge into the first tier and form vegetation communities similar to those that existed before the violation.[...]
The problem of succession has been studied most deeply in phytocenoses, primarily because changes in communities are based on the functions of autotrophs, while heterotrophic changes are secondary and follow autotrophs.[...]
To the west of the Rocky Mountains, large areas of the lowlands are covered with thickets of semi-desert subshrubs. Sagebrush communities rise to the lower parts of the foothills; Higher up the slopes scattered individual bushes of low-growing juniper. Even higher in the mountains, where juniper becomes larger and more numerous and grows together with edible pine, open low-trunked woodlands with a cover of cereals and shrubs in the lower tier are formed. With further ascent into the mountains, the open forest becomes more and more closed, and individual ponderosa pine trees appear in it. Further, the number of edible pine and juniper decreases, and yellow pine increases, and a pine forest is formed. Gradually, ponderosa pine gives way to Douglas fir and white fir, which in turn are replaced by forests of Engelmann spruce and alpine fir. Then, when crossing the uppermost belt of mountain forests, the trees decrease in size and turn into shrubs, forming clumps among the meadow vegetation. Above the forest line there are alpine meadows in the highlands. They extend upward, but do not form a continuous cover with height and are eventually replaced by communities of lichens with a few herbs, huddling among the rocks.[...]
In cases where the main species - environment-formers - drop out of the biocenosis, this leads to the destruction of the entire system and a change in communities. Sometimes such changes in nature are made by none other than man, by cutting down forests, overfishing in water bodies, etc. [...]
F. Clements’ statement about the exceptional importance of climate as driving force successions. Changes in communities can also occur under the influence of other factors - such as changes in relief, soil, hydrological regime, etc. The most important importance in modern ecology is given to biocenotic factors of succession: plant species (as well as animals) participating in successional communities change living conditions for other species, thus “preparing the ground” for the subsequent stage of succession.[...]
Energy resource in developing and mature ecosystems. As succession progresses, an increasing proportion of available nutrients accumulates in the biomass of the community, and accordingly their content in the abiotic component of the ecosystem (soil or water) decreases. In a young forest, excess biomass is produced, which accumulates in the form of wood (respiration does not destroy all the production, and it is formed faster than it is oxidized). In the forest, this can be observed firsthand: during succession, tree trunks thicken year after year. The upper limit of biomass accumulation is reached when the total respiration losses (I) become almost equal to the total primary productivity (P), that is, the P/I ratio approaches unity. As communities change in the later stages of succession, productivity increases, but during the transition to a climax community there is usually a decrease in overall productivity (Fig. 2.33).[...]
The trophogenic series is a series of increasing richness of the substrate from quartz sands and apigotrophic peats to various loamy and carbonate deposits with a corresponding natural change of communities from poor pine forests to rich oak forests, bushes, fir and spruce-ramen forests with an admixture of deciduous trees. During this series, as the trophicity of sediments increases, light-loving oligo-mesotrophs are consistently replaced by shade-tolerant mesotrophs and megatrophs with a constant increase in the overall productivity of plant groups.[...]
Ecosystem dynamics is a change in an ecosystem (biogeocoenosis) under the influence of external forces and internal processes of its development. Secular dynamics of an ecosystem are distinguished - relatively reversible or irreversible changes in communities caused by various (periodic) factors, occurring over a very long (many centuries) time interval. Seasonal dynamics of ecosystems, as a rule, are associated with the change of seasons of the year and represent one of the forms of cyclical (periodic) changes in the community (diurnal, seasonal, weather-temperature, etc.). Anthropogenic ecosystem dynamics are also distinguished, i.e., the change of communities under the influence of human activity (succession).[...]
General concepts about successions. The development of the problem of succession began in botany, and to this day the main provisions of this concept are based on the study of phytocenoses. This is determined not only by historical reasons, but also by the fact that changes in communities are based on the functions of autotrophs. The heterotrophic component of biocenoses is formed on the basis of the phytocenosis and only secondarily begins to influence its composition and properties.[...]
In the reservoirs of the river. In the Volga region, the values of the pigment index E48o/E664 vary in the same range, the average is close to unity (Table 19), indicating that phytoplankton functions within its physiological norm. In the seasonal cycle, the predominance of carotenoids over chlorophyll is observed in early summer (E480/E664 >1), which is typical for periods of decline in the development of algae when communities change. In August, the pigment index decreases and fluctuates around one. In October, the E48o/Ebb4 values remained unchanged in the Gorky and Cheboksary reservoirs, but increased significantly in the Kuibyshev, Saratov and Volgograd reservoirs. As noted above, the pigment index shows the same trends as the percentage of chlorophyll derivatives. The change in both indicators corresponds to the degree of phytoplankton development. During seasonal maximums, viable active cells are present in the reservoir, signs of physiological well-being of which are reduced values of pigment characteristics: the predominance of green pigments over yellow ones (E480/E664 is below or slightly above unity), as well as the presence of an active form of chlorophyll (low relative content of pheopigments) . At low chlorophyll concentrations, indicating a decline in community development, both indicators increase.[...]
If a disturbing factor, after which the development of biocenoses begins, appears with a certain periodicity, then they speak of cyclic succession. It is a biological consequence of the influence of a natural climatic factor external to the biocenosis. During cyclic successions, it is not biocenoses that change the habitat, but it is the variability of the physical environment that is the factor that determines the change in communities in biocenoses at different phases of the natural cycle.
