No community exists forever, sooner or later it is replaced by another community. This occurs when exposed to external causes or as a result of changes in the environment due to the vital activity of organisms that form biocenoses, including when new species are introduced into communities. Among the diverse forms of swept communities, primary and secondary successions are distinguished. Primary successions are a natural succession of communities in areas not previously occupied by vegetation, for example, on sandbanks in floodplains, in places freed up after the retreat of glaciers, etc. Depending on the substrate (its physical and chemical properties) either only bacteria, algae and lichens settle here at first, or vascular plants along with them.[ ...]
Such changes in communities are called successions. In the process of primary successions, and natural communities, and soil.[ ...]
The described change of communities occurs within 60-80 years. The stability of such communities is determined by a number of reasons: firstly, by the composition of the community by plants with strong environment-forming properties, which limit the possibility of introducing new species into it. At the same time, the conditions for the renewal of those species that make up the community are sufficient. Second, sustainable ecosystems have a well-balanced and diverse set of animal species. Interactions of populations in such communities are diverse and well adapted to living together. There are practically no opportunities for the introduction of new species. All these properties of a stable community ensure its long existence.[ ...]
A classic example of a change in communities under the influence of the vital activity of organisms is the process of overgrowing of lakes. In the water of any lake, especially if it is rich in nitrogen and ash elements, a huge number of microscopic organisms (algae, protozoa, etc.) live. When dying, 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 of sunlight to the bottom of the lake. As a result, conditions are created for the settlement of mosses and multicellular algae, which causes an acceleration of the accumulation of organic residues (sapropel peat) on the bottom of the lake and leads to an 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 (weeds, water lilies, egg capsules, etc.). The next stage of overgrowing of the lake is the settlement of lake reeds and common reeds, which develop a huge mass of above-ground shoots, from which, after their death, reed or reed peat is formed. With further filling of the lake with dead plant remains and its shallowing, sedges settle. The lake gradually turns into a swamp. Observing individual belts of aquatic vegetation on an overgrown lake, one can restore the main stages of its overgrowth - the 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 have shown that the formation of phytocenosis begins with mosses and sedges; following them, creeping, and then shrubby forms of willows are included in the community. Later (after about 20-25 years) raspberries appear; spruce appears after them, which forms the basis of the final community in the form of a mixed forest, which is formed 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 act in one direction for a long time, for example, the increasing drying up of swamps as a result of melioration, increasing anthropogenic pollution of water bodies, and increased grazing. The resulting change of one biocenosis to 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, which consists in the consistent use of decaying organic matter by various types. The peculiarities of such successions are that communities consist only of heterotrophic organisms, and the course of successions is directed towards an increasing structural and chemical simplification of clusters. organic matter.[ ...]
So, succession is a natural, consistent change of communities in ecosystems, due to the influence of a complex of internal and external factors. Changes over time are 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 that is most adapted in relation to the complex climatic conditions, which he called "climax - formation" or simply "climax"; at present, 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. Progressive successions are distinguished, in which species diversity is gradually increasing, but there are also digressions - regressive successions aimed at uniting and simplifying communities. Especially often the latter began to manifest itself in the presence of large-scale adapted impacts on biocenoses that violate the optimum conditions.[ ...]
The development of biocenoses, in which there is a replacement in time of one community by another, is called ecological succession1. In most cases, succession processes take time intervals measured in years and decades, although in some cases, community changes follow 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: the number of community changes, additivity, independence from alpha diversity, and independence from excessive sample size. The degree of measurement by each species change index was estimated by calculating the -diversity for two hypothetical gradients, one of which is homogeneous (i.e. [ ...]
When the vegetation is destroyed without changing the soil and ground conditions, the communities change in the direction of returning to the state that characterizes the original root type. For example, when coniferous forests are destroyed in clearings or burnt areas, grasses first grow (reed grass, willow-herb, etc.), and then plantations of small-leaved species (birch, aspen) gradually form, under the canopy of which spruce or other conifers settle, which subsequently emerge into the first tier and form plant communities similar to those that existed before the disturbance.[ ...]
The problem of successions has been worked out most deeply in phytocenoses, primarily because community changes are based on the functions of autotrophs, while heterotrophic changes are secondary and follow autotrophs.[ ...]
To the west of the Rocky Mountains, large areas of lowland are covered with thickets of semi-desert semi-shrubs. Sagebrush communities rise to the lower parts of the foothills; Higher up the slopes are scattered individual bushes of low-growing juniper. Even higher in the mountains, where the juniper becomes larger and more numerous and grows together with the edible pine, open low-stemmed light forests are formed with a cover of grasses and shrubs in the lower tier. With further ascent to the mountains, the light forests are more and more closed, and individual yellow 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, yellow pine gives way to douglas and silver fir, which in turn are replaced by forests of Engelmann spruce and alpine fir. Then, when passing through the uppermost belt of mountain forests, the trees decrease in size and turn into shrubs, forming clumps among the meadow vegetation. Alpine meadows of high mountains are located above the forest line. They extend upwards, but do not form a continuous cover with height and eventually give way to communities of lichens with a few herbs nestling among the rocks.[ ...]
In those cases when the main species - environment-forming species - fall out of the composition of the biocenosis, this leads to the destruction of the entire system and the change of communities. Sometimes such changes in nature are produced by none other than man, cutting down forests, overfishing in reservoirs, etc.[ ...]
The statement of F. Clements 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 topography, soil, hydrological regime, etc. 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 accumulate 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, an excess of biomass is produced, which accumulates in the form of wood (respiration does not destroy all production, and it is formed faster than it oxidizes). In the forest, this can be observed with your own eyes: in the course of succession, tree trunks thicken from year to year. The upper limit of biomass accumulation is reached when the total respiration loss (R) becomes almost equal to the total primary productivity (R), i.e. the P/R ratio approaches unity. As communities change in the later stages of succession, productivity increases, but when moving 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 peat to various loamy and carbonate deposits with a corresponding regular change in communities from poor forests to rich oak forests, buchins, fir and ramen spruce forests with an admixture of shrimp-leaved woody pores. Throughout this series, as the trophicity of the deposits increases, the successive displacement of light-loving oligo-mesotrophs by shade-tolerant mesotrophs and megatrophs occurs with a constant increase in the overall productivity of plant groups.[ ...]
Ecosystem dynamics - a change in the ecosystem (biogeocenosis) under the influence of forces from the outside and internal processes of its development. The secular dynamics of the ecosystem is distinguished - relatively reversible or irreversible changes in communities caused by various (periodic) factors that occur over a very long (many centuries) interval of time. The seasonal dynamics of ecosystems, as a rule, is associated with the change of seasons and is one of the forms of cyclic (periodic) changes in the community (daily, seasonal, weather-temperature, etc.). They also distinguish the anthropogenic dynamics of the ecosystem, i.e. the change of communities under the influence of human activity (succession).[ ...]
General concepts about successions. The development of the problem of successions began in botany, and to this day the main provisions of this concept are based on the study of phytocenoses. This is determined not only by historical reasons, but also by the fact that community changes are based on the functions of autotrophs. The heterotrophic component of biocenoses is formed on the basis of phytocenosis and only secondarily begins to influence its composition and properties.[ ...]
In the reservoirs Volga, the values of the pigment index E48o/E664 vary in the same range, the average values are close to unity (Table 19), indicating that phytoplankton functions within their physiological norm. In the seasonal cycle, the predominance of carotenoids over chlorophyll is observed at the beginning of 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 E480/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 is characterized by the same trends as the percentage of chlorophyll derivatives. The change in both indicators corresponds to the degree of phytoplankton development. During seasonal maxima, viable active cells are present in the reservoir, the signs of physiological well-being of which are reduced values of pigment characteristics: the predominance of green pigments over yellow ones (E480 / E664 below or slightly above unity), as well as the presence of the active form of chlorophyll (low relative content of pheopigments) . At low concentrations of chlorophyll, indicating a decline in the development of the community, both indicators increase.[ ...]
If the perturbing factor, after which the development of biocenoses begins, manifests itself with a certain periodicity, then one speaks of cyclic succession. It is a biological consequence of the influence of a natural and climatic factor external to the biocenosis. In 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 of communities in biocenoses during different phases of the natural cycle.
The composition of ecosystems is a dynamic process. Ecosystems are constantly undergoing changes in the state and vital activity of their members and the ratio of populations. The diverse changes that take place in any community are classified into two main types: cyclical and progressive.
Cyclical changes communities reflects the daily, seasonal and long-term periodicity external conditions and manifestation of internal (endogenous) rhythms of organisms.
Daily cycles are associated mainly with rhythm. natural phenomena and is strictly periodic. Seasonal variability of biocenoses is expressed in a change not only in the state and activity, but also in the quantitative ratio certain types depending on the cycles of their reproduction, seasonal migrations, the death of individual generations during the year.
seasonal variability the tiered structure of the biocenosis is often also affected: individual tiers of plants can completely disappear in the corresponding seasons of the year, for example, a herbaceous tier consisting of annuals.
Long-term cyclicity depends on changes in meteorological conditions over the years (climatic fluctuations), uneven precipitation over the years, with periodic recurrence of droughts, or other external factors affecting the community (for example, the degree of river flooding). In addition, the long-term periodicity may be related to the features life cycle edificatory plants, with the repetition of mass reproductions of animals or microorganisms pathogenic for plants, etc.
Progressive changes in a community lead ultimately to the replacement of this community by another, with a different set of dominant species. The reason for such changes may be factors external to the cenosis that act in one direction for a long time, for example, the drying up of marsh soils, increasing pollution of water bodies, increased grazing, etc. as a result of reclamation. The resulting changes of one biocenosis to another are called exogenetic. Endogenetic shifts arise as a result of processes occurring within the community itself.
Successions
Sequential shift one biocenosis is called another (from lat. Succession - sequence, change) - succession. Succession is a process of self-development of ecosystems. Succession is based on the incompleteness of the biological cycle in a given biocenosis. Every living organism, as a result of its vital activity, changes its environment around itself, removing some substances from it and saturating it with metabolic products. With a more or less long-term existence of populations, they change their environment in an unfavorable direction and, as a result, are forced out by populations of other species, for which the resulting environmental transformations turn out to be ecologically beneficial. Thus, in the community there is a change in the dominant species. A successive series of communities gradually and regularly replacing each other in succession is called successional series.
Distinguish between primary and secondary succession. primary succession begins on places deprived of life (on rocks, sands, cliffs). secondary succession- this is a successive change of one community that existed on a given substrate by another more perfect for these abiotic processes. Secondary successions, as a rule, take place faster and easier than primary ones, since the soil profile, seeds, primordia, and part of the former population and former connections are preserved in the disturbed habitat.
In any successional series, the rate of change gradually slows down. The end result is the formation of a relatively stable stage - climax community or menopause. The initial, pioneer groupings of species are characterized by the greatest dynamism and instability. Climax ecosystems, on the other hand, are capable of long-term self-maintenance in the appropriate range of conditions, as they acquire such features of the organization of biocenoses that allow maintaining a balanced circulation of substances.
7. Artificial ecosystems: agro- and urban ecosystems
A person receives a lot of products from natural systems, however, agriculture is the main source of food for him.
Agroecosystems are created by man to obtain a high yield - pure production of autotrophs. Summarizing everything that has already been said about agroecosystems, we emphasize the following main differences from natural ones:
1. They have a sharply reduced diversity of species: a decrease in the species of cultivated plants also reduces the species diversity of the animal population of the biocenosis; the species diversity of animals bred by man is negligible compared to the natural one; Cultivated pastures (with undersowing of grasses) are similar in species diversity to agricultural fields.
2. Plant and animal species cultivated by man "evolve" through artificial selection and are not competitive in the fight against wild species without human support.
3. Agro-ecosystems receive additional energy subsidized by man, in addition to solar energy.
4. Pure products (crop) are removed from the ecosystem and do not enter the food chains of the biocenosis, and its partial use by pests, losses during harvesting, which can also fall into natural trophic chains, are suppressed in every possible way by humans.
Ecosystems of fields, gardens, pastures, kitchen gardens and other agrocenoses are simplified systems maintained by man in the early stages of succession, and they are just as unstable and incapable of self-regulation as natural pioneer communities, therefore they cannot exist without human support. .
More than 50% of the world's population lives in cities today. Process urbanization- this is the growth of the urban population, the number and size of cities, the increase in the role of the city in people's lives, the spread of the urban lifestyle. Today, urbanized territories occupy 1% of the land, but concentrate 50% of the world's population, produce 80% gross product(GDP) account for 80% of all emissions.
metropolis It is an overgrowth of cities. The relationship of all components and phenomena of the urban and natural environment is called urban ecosystem. Urban ecosystems have a specific place in geographic space. These are open systems, managed. Their important feature is anthropocentrism.
Relationships between organisms in a biocenosis
There are the following types of consortia:
– individual (one plant),
– cenopopulation (populations of a species in a plant community),
– regional,
- species.
Relations between organisms in a biocenosis are also determined by the time they spent in the community.
They can be permanent (sessile) or temporary (vagile). Constancy characterizes mainly plants, since animals in most cases stay in the community temporarily during the day, season or during the migration period.
According to Beklemishev, interspecific relations are divided into four types: trophic, topical, phoric and factory.
Trophic connections arise when one species feeds on another (either living individuals or their remains and waste products).
The forest is a separate biocenosis. Photo: Scott Wylie
Topical connections characterize any physical or chemical change in the living conditions of one species as a result of the life activity of another. They consist in the creation of one type of environment for another, in the formation of a substrate, in influencing the movement of water, air, in changing temperature, saturating the environment with excretion products, etc.
Phoric connections are the participation of one species in the distribution of another.
Factory connections - when one species uses the products of excretion or remains, or even living individuals of another species, to build its structures.
Dynamics of biocenoses
In general, the community is characterized by diurnal, seasonal (annual) and long-term dynamics, which are characteristic of both plants and animals. The daily cycle, caused by the change of light and dark parts of the day, in plants is manifested in the intensity of photosynthesis, respiration, opening and closing of flowers, in animals - in different daily activities (day, twilight and night).
Often, animals change community during the day. Thus, the heron feeds in the shallow waters of reservoirs, and nests and spends the night in the crowns of trees, pollinating insects (for example, bees) can fly from the forest community to the meadow community.
The seasonal dynamics of the biocenosis depends on the phenological state of the phytocenosis, the species composition and the number of animals living in it. Each type of plant organisms during the growing season goes through certain stages of development (the beginning of the growing season, flowering, fruiting and dying off). In a phytocenosis consisting of many species, the phases of plant development may or may not coincide.
The appearance of a phytocenosis, which changes throughout the year with alternating phases of development, is called an aspect. As a rule, the aspect is repeated from year to year with the same sequence, reflecting the color scheme of the plant community (spring bright greenery, summer colors and autumn variegation of forests). The aspect is usually named after the plants that give the phytocenosis the most noticeable color, for example, the blue aspect of the marsh forget-me-not, the white aspect of cotton grass, the brown aspect of sedge leaves, etc.
The seasonal dynamics of animal representatives of the biocenosis is associated with their reproduction, vital activity and migration. The spring arrival and autumn departure of birds, fish spawning, the appearance of young animals, the activity of pollinating insects in the meadows, the winter hibernation of the bear are only a negligible part of the examples of the seasonal dynamics of the animal population of the biocenosis.
The long-term dynamics of the community is caused by its repeated changes over several years in the absence of a sharp change in the species composition. Changes mainly affect the number of individuals of the species that form the biocenosis. As an example, we can cite changes in the forests of some reserves in Belarus and Russia, due to an increase in the number of elk, the main consumer of tree and shrub fodder. For a year, an elk eats about 7 tons of feed, and more than half are shoots of deciduous and coniferous species. With an increase in the density of the animal, damage to the undergrowth increases. There comes a period when the young generation of the forest stand is almost completely destroyed in the forest plantation. Due to starvation, moose are forced to leave such areas of the forest.
Stages of formation of biocenoses
The emergence of biocenosis begins with the appearance of the first organisms in areas deprived of life (lava flows, volcanic islands, talus, exposed rocks, sandy deposits and dried bottoms of reservoirs). Settlement begins with an accidental introduction of organisms from territories already developed by them and depends on the properties of the substrate. This site for many seeds of plants and animals that have penetrated here may not be suitable for reproduction. Often, especially in the humid zone, the first settlers are representatives of algae, mosses and lichens.
As a rule, only a few of the introduced plant species develop successfully. Animals-consumers settle somewhat later, since their existence without food is impossible, but an accidental visit by them to the developed areas is a rather frequent occurrence. This stage of development of biocenosis is called pioneer. Although the community has not yet formed at this stage (inconsistent species composition, sparse vegetation), it already has an impact on the abiotic environment: soil begins to form.
The pioneer stage is replaced by an unsaturated one, when plants begin to renew themselves (by seeds or vegetatively), and animals multiply. 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 significant role. This stage of development of the biocenosis is a grouping.
With the subsequent development of the community, the vegetation cover is differentiated by tiers and synusia, its mosaic pattern, species composition, food chains and consortia. Ultimately, all ecological niches are occupied, and further introduction of organisms becomes possible only after the displacement or destruction of the old-timers. This final stage of biocenosis formation is called saturated. However, the further development of the biocenosis does not stop and random deviations in species composition and relationships between organisms and with environment may still take place.
Random deviations in the structure of the biocenosis are called fluctuations. As a rule, they are caused by random or seasonal changes in the number of species included in the biocenosis as a result of adverse meteorological phenomena, floods, earthquakes, etc. Heavy snowfalls and hoarfrost, for example, lead to crown thinning, and in spring cereals. Spring frosts and late spring snow cover not only damage flowering plants, which affects their fruiting, but also often cause mass death of migratory birds. strong winds, floods and earthquakes cause disturbances in biocenoses, after which it takes a long time to restore the community.
Although the biocenosis is a rather conservative natural system, however, under the pressure of external circumstances, it can give way to another biocenosis. The successive change in time of some communities by others in a certain 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 its original state. The interaction of organisms, mainly wounds, with each other and with the environment leads to succession.
Successions are divided into primary - historical. Primary ones occur on soils that are primarily free from soil - volcanic tuff and lava fields, loose sands, stony placers, etc. As the phytocenosis develops from the pioneer stage to saturated, the soil becomes more fertile and more and more involved in the biological cycle chemical elements in increasing numbers. With an increase in fertility, plant species that develop on nutrient-rich soils displace less demanding species in this regard. At the same time, the animal population also changes. Secondary successions are carried out in the habitats of destroyed communities, where soils and some living organisms have been preserved. The destruction of biocenoses can be caused by natural processes (hurricanes, downpours, floods, landslides, prolonged droughts, volcanic eruptions, etc.). as well as changes in the habitat by Organisms (for example, when a reservoir is 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 sandy soils, abundant natural regeneration of spruce begins, which will eventually displace pine, provided that regular clear-cutting of pine stands and silvicultural work are not carried out. On burnt areas with sandy and loamy soils, pioneer vegetation of willow-herb and warty birch eventually gives way to spruce plantations.
In recent decades, large-scale drainage and irrigation works have acquired particular importance in changing the vegetation cover. In swamp forests that are in the zone of influence of drainage channels, hygrophyte plants disappear (sedge ols, for example, are transformed into nettles). The transformation of the species composition, including the animal population, also affects the forests arriving to the drained swamps. Irrigation reclamation, on the contrary, contributes to 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 effect on biocenoses. All these changes are secondary successions.
The change of one biocenosis to another during the succession forms a successional series, or series. The study of successional series is of great importance in connection with the increasing anthropogenic influence on biocenoses. The end result of this kind of research can 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 the 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 a balance is maintained between organisms, as well as between them and the environment - to the 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 X. Kauls 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 soil of a certain type - pedoclimax. Successions leading to this stage are called progressive, and those that remove the biocenosis from it are called regressive. It is impossible, however, to give the concept of "climax" an absolute meaning and to believe that when it is reached, the community stops development.
Biocenoses that, when disturbed, return to their original state, are called indigenous. A birch forest will grow on the site of felling of blueberry pine forest or sour spruce forest, and it, in turn, will again be replaced by blueberry pine forest or sour spruce forest. In this case, we are talking about indigenous forest types.
Transformed biocenoses do not return to their original state. Thus, a low-lying sedge bog, drained and developed for crops, after the depletion of the peat deposit and the destruction of the reclamation network, with the cessation of agricultural use for some reason, develops in the direction of the formation of birch or alder undergrowth. The zoocenosis of this small forest differs from the animal species community of the open grassy swamp.
Classification of biocenoses
For the purpose of scientific knowledge of biocenoses and practical application communities of organisms need to be classified according to their relative size and complexity of organization.
The classification is designed to put in order all their diversity with the help of a system of taxonomic categories, i.e. taxa, uniting in this case 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 simple taxa 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 indicative features. For example, a raised bog with rosemary–moss cover and a low-growing pine stand contrasts with the surrounding pine forest community on sandy soils. The boundary between the forest and the meadow is also clearly visible. However, since the conditions for the existence of communities change more gradually than the communities themselves, the boundaries of biocenoses are usually blurred. The gradual transition from one phytocenosis to another with their proximity and the change of one phytocenosis by another in time is reflected in the concept of a continuum (from Latin continuum - continuous) of vegetation developed by the Soviet geobotanist L. G. Ramensky, the American ecologist P. X. 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 role of herbaceous species in transforming the environment is less contrasting.
The classification of communities uses taxonomic categories adopted in plant geography and based on the identification of dominants and edificators, which indicates the recognition of phytocenosis as an ecological framework that determines the structure of biocenosis. The taxonomic system of communities built on dominants and edificators can be expressed as follows: association - group of associations formation group of formations class of formations type of biome - biocenotic cover.
The lowest taxonomic category is association. It is a collection of homogeneous microbiocenoses with the same structure, species composition and similar relationships both between organisms and between them and the environment. Under field conditions, the main features of its identification are: the same layer structure, similar mosaic (spotted, scattered), coincidence of dominants and edificators, as well as the relative uniformity of the habitat. The name of an association for multilevel 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 last , for example, a caustic-meadow-bluegrass association. Usually meadow associations are designated in Latin: Ranunculus + Poa pratensis.
The group of biocenotic associations is formed by associations that differ in the composition of one of the tiers. The bilberry pine forest, for example, combines associations with an undergrowth layer of juniper, buckthorn, and birch undergrowth. The group of grass–sedge–forb associations includes meadow communities with a set of named groups of meadow grasses (grasses, small sedges, forbs).
The biocenotic formation includes groups of associations. The formation is distinguished by the dominant, according to which it is called: the formation of Scots pine, black alder, English oak, white saxaul, caustic buttercup, wormwood, etc. This is the main unit of the middle rank, widely used in mapping forest vegetation.
A formation group is all formations whose dominants belong to the same life form. Since the life forms of plants are extremely diverse, the volume of groups of formations is heterogeneous: dark coniferous, light coniferous, deciduous, evergreen, small-leaved and broad-leaved forests; large-grass, small-grass, low-grass, small-forb and other groups of meadow formations.
The class of formations is formed by all groups of formations, the dominants of which have ecologically similar life forms, for example, coniferous forests (with a needle blade), deciduous forests, etc.
The type of biome (biocenotic type) combines classes of formations. Biome types are tundra, forest tundra, taiga, grasslands, steppes, deserts, prairies, wet rainforests etc.
The biocenotic cover is the highest taxonomic unit, including all types of land biomes.
In the botanical and geographical literature, there are other classifications of phytocenoses. For the aquatic environment, in which the role of vegetation is limited, the allocation of taxonomic categories of biocenoses is based on the animal population.
Each biogeocenosis has its own spatial structure, which is expressed in tiers in the vertical direction, and in synusia in the horizontal direction. The ongoing interactions and interchanges of the components of biogeocenosis (atmosphere, soil and rocks, water, animal and flora and microorganisms) cause its continuous development, which leads to the replacement of some biogeocenoses by others - to successions. Ultimately, the destruction of some communities and the creation of new ones determines the continuous development of the biogeocenotic cover of the Earth. Over time, the continuous change in a separate biogeocenosis slows down, as the process of the introduction of new organisms weakens and the climax stage begins.
Self-development of biogeocenosis, determined by internal (endogenous) processes, is disturbed by external (exogenous) influences, resulting in new successional series. Among the most important exogenous factors includes human activity, but the person himself is not among the components of biogeocenosis.
Biogeocenoses are elementary cells of the biogeosphere (biogeocenotic cover) - the shell of the Earth, in which the living matter of the planet is concentrated. The biogeosphere is the only shell of the Earth in which a permanent presence and normal all-round human activity are possible.
1. Continue the definition: "An ecosystem is..." Options:
1) a set of various populations that remain indefinitely interacting with each other and the environment
2) the relationship 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. The gross primary production of an ecosystem is called:
1) the total amount of matter and energy coming from autotrophs to heterotrophs
2) the total amount of matter and energy produced by autotrophs
4. Primary production in ecosystems is formed by:
1) producers 3) detritophages
2) consumers 4) decomposers
5. Secondary production in ecosystems is formed:
3) detritophages
4) decomposers
1) producers
2) consumers
3. The lowest productivity is typical for ecosystems:
4) deserts
7. The highest productivity is typical for ecosystems:
1)Tropical rain forest
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) the central parts of the ocean
3) mountain forests
2) temperate forests
4) coral reefs
1, 3, 2, 4
9. Arrange the following ecosystems in order of increasing productivity:
1) moist forests 3) steppes
2) oak forests 4) arctic tundra
4, 2, 3, 1
10. Despite the fact that the ocean occupies 71% of the area of 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 this be explained?
(The main land producers are trees, and the oceans are small unicellular algae; different growth; herbivorous consumers of the ocean quickly eat producers, and the algae supply is constantly low, but on land it is vice versa)
11. List the principles of functioning of ecosystems.
(Obtaining resources and getting rid of waste within the cycle of all elements; existence at the expense of practically inexhaustible and clean solar energy; correspondence of the biomass of the population to the trophic level occupied by it)
12. Describe the phenomena that testify to the human violation of the principles of functioning of ecosystems.
(Violation 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 - there cannot be a large biomass at the end of long food chains. Man is the third trophic level, i.e., he eats meat.In order for all people to 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 of:
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 activity of:
1) denitrifying bacteria
2) sulfobacteria
3) methylotrophic bacteria
4) sulfur bacteria
15. Nitrogen enters plants in the process of cycling in the form of:
1) nitric oxide 3) nitrates
2) ammonia 4) nitric acid
16. The main anthropogenic sources of sulfur entering the large circulation of substances are:
1) thermal power plants
2) fertilizer
3) testing of 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 circulation of living organisms
4) nitrogen cycle
18. Determine which cycle (nitrogen, sulfur cycle) corresponds to each feature (1-6). Establish a correspondence between the circulation of substances and their signs:
A, B, A, B, B, A
19. In the terrestrial biocenosis, microorganisms and fungi complete the decomposition of organic compounds to simple mineral components, which are again involved in the circulation 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 as part of:
1) carbon dioxide 3) limestone
2) free carbon
21. Carbon leaves the cycle of matter (forming sedimentary rocks) as part of:
1) calcium sulfate 3) calcium nitrate
2) calcium carbonate
4) calcium sulfide
22. The complete cycle of oxygen in nature lasts about:
2) 2000 years
3) 1 million years
4) 100 million years
23. A complete water cycle in nature lasts about:
3) 1 million years
4) 100 million years
24. The rule of the edge (boundary) effect says: 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 weight 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 the deserts 4) in the tropics
27. The frequency of opening and closing oyster shells is referred to as rhythms:
1) daily 3) annual
2) tidal
4) seasonal
28. Falling leaves are classified as rhythms:
1) lunar 3) seasonal
2) daily 4) annual
29. The successive change of some communities by others in a certain area of the environment is called:
1) succession 3) menopause
2) fluctuation 4) integration
30. Examples of primary succession listed include:
1) turning abandoned fields into broad-leaved forests
2) gradual change of clearings by deciduous forest
3) gradual overgrowth of bare rock with lichens
4) the transformation of fires into spruce forests
31. Among the listed successional processes, primary succession includes:
1) turning burnt areas into spruce forests
2) gradual change of clearings by pine forest
3) transformation of degraded pastures into oak forests
4) the appearance of a pine forest on the loose sands
32. Among the listed successional processes, secondary succession is considered:
1) turning abandoned fields into oak forests
2) the appearance of lichens on cooled volcanic lava
3) gradual overgrowth of bare rock
4) the appearance of a pine forest on the loose sands
33. The main cause of ecosystem instability is (are):
1) unfavourable conditions environments
2) lack of food resources
3) imbalance of the circulation of substances
4) an excess of certain species
34. A relatively stable state of an ecosystem, in which a balance is maintained between organisms, as well as between them and the environment, is called:
1) 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 reservoirs with nutrients that stimulate the growth of phytoplankton
2) the process of turning a swamp into a lake
3) the process of water enrichment with oxygen
Topic 7. Biosphere
1. The shell of the Earth, containing the totality of living organisms and that part of the planet's substance that you find: continuous exchange with these organisms, is called:
1) atmosphere 3) ecosphere
2) hydrosphere 4) biosphere
2. Which of the following is not included (in whole or in part) in the composition of the biosphere:
1) atmosphere 4) lithosphere
2) magnetosphere 5) asthenosphere
3) hydrospheres 6) ionosphere
3. At what height is the so-called individual 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 UV protection
2) in maintaining the planet's climate
3) in creating the greenhouse effect
5. Indicate three substances, the content of which in the earth's crust is maximum:
1) hydrogen
2) aluminum
3) oxygen
4) calcium
5) silicon
6. Distinctive features oceanic crust (compared to the mainland):
1) thickness 3-7 km
2) thickness 20-40 km
3) a granite layer is present
4) no granite layer
5) sedimentary layer less than 1 km on average
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. Describe the shells of the Earth that make up the biosphere.
(Atmosphere(Earth's gaseous envelope) 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(the water shell of the Earth) makes up 70% of the Earth's surface. The largest water reserves are concentrated in the World Ocean (about 90%). The state of the hydrosphere determines climatic conditions.
Lithosphere(the 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.
(Gas function - the release and absorption of gases by living organisms.
The emergence of biocenosis begins with the appearance of the first organisms in areas deprived of life (lava flows, volcanic islands, talus, exposed rocks, sandy deposits and dried bottoms of reservoirs). Settlement begins with an accidental introduction of organisms from territories already developed by them and depends on the properties of the substrate. This site for many seeds of plants and animals that have penetrated here may not be suitable for reproduction. Often, especially in the humid zone, the first settlers are representatives of algae, mosses and lichens.
As a rule, only a few of the introduced plant species develop successfully. Animals-consumers settle somewhat later, since their existence without food is impossible, but an accidental visit by them to the developed areas is a rather frequent occurrence. This stage of development of biocenosis is called pioneer. Although the community has not yet formed at this stage, it already has an impact on the abiotic environment: soil begins to form.
The pioneer stage is replaced by an unsaturated one, when plants begin to renew themselves (by seeds or vegetatively), and animals multiply. 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 significant role. This stage of development of the biocenosis is a grouping.
With the subsequent development of the community, the vegetation cover is differentiated by tiers and synusia, and its mosaic structure, species composition, food chains, and consortia acquire stable constancy. Ultimately, all ecological niches are occupied, and further invasion of organisms becomes possible only after the displacement or destruction of the old-timers. This final stage of biocenosis formation is called saturated. However, the further development of the biocenosis does not stop, and random deviations in the species composition and relationships both between organisms and with the environment can still occur.
Random deviations in the structure of the biocenosis are called fluctuations. As a rule, they are due to random or seasonal changes in the abundance 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, however, under the pressure of external circumstances, it can give way to another biocenosis. The successive change in time of some communities by others in a certain area of the environment is called succession. As a result of succession, one community is successively replaced by another without returning to its original state. The interaction of organisms, mainly wounds, with each other and with the environment leads to succession.
Successions are divided into primary-historical. Primary ones occur on soils that are primarily free from soil - volcanic tuff and lava fields, loose sands, stony placers, etc. As the phytocenosis develops from the pioneer stage to saturated, the soil becomes more fertile and more and more chemical elements are involved in the biological cycle in increasing quantities. With an increase in fertility, plant species that develop on nutrient-rich soils displace less demanding species in this regard. At the same time, the animal population also changes. Secondary successions are carried out in the habitats of destroyed communities, where soils and some living organisms have been 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 soils, abundant natural regeneration of spruce begins, which will eventually displace pine, provided that regular clear-cutting of pine stands and silvicultural work are not carried out.
The change of one biocenosis to another during the succession forms a successional series, or series. The study of successional series is of great importance in connection with the increasing anthropogenic influence on biocenoses. The end result of this kind of research can 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 the 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 a 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 X. Kauls and is widely used in foreign botanical and geographical literature. According to this concept, the climax is the terminal stage of community evolution, which corresponds to a soil of a certain type - pedoclimax. Successions leading to this stage are called progressive, and those that remove the biocenosis from it are called regressive.
Biocenoses that, when disturbed, return to their original state, are called indigenous.
Transformed biocenoses do not return to their original state.
