When does interspecies competition occur? Territoriality in animals. Ways to limit your territory by different animals. Examples of competitive relations in nature

In the last two decades, there has been a fierce debate in the ecological literature about the role of competition in limiting the distribution and dynamics of natural populations of different species, and, consequently, in determining the structure of communities. According to some researchers, the populations included in natural communities are quite strictly controlled by a system of competitive relations, sometimes, however, modified by the influence of predators. Others believe that competition between representatives of different species is observed in nature only occasionally, and populations, for the most part, being limited by other factors, as a rule, do not reach those densities at which competitive relations become decisive. There is also a not unfounded compromise point of view, which assumes the existence of a certain continuum of real natural communities, at one end of which there are communities that are stable in time, rich, or, more precisely, saturated with species, tightly controlled by biotic interactions, and at the other, communities that are unstable ( in most cases, due to the fact that abiotic conditions in their habitats are not stable), not saturated with species (that is, allowing the introduction of new species) and controlled, as a rule, by poorly predictable changes in external conditions.

Obtaining direct evidence of the importance of the role of competition in determining the dynamics and distribution of populations in nature is very difficult. Usually we can judge this only on the basis of indirect evidence, but we note that the circumstantial nature of certain evidence should not in itself serve as a basis for ignoring them. In those cases where a number of independently obtained circumstantial evidence is built into a logically justified and not contrary to common sense scheme, this scheme should not be rejected on the sole ground that there is no direct evidence. It should also be emphasized that it is not very often possible to directly observe the process of competition in nature. The bulk of the available evidence of competition concerns such a distribution of species relative to each other in space or time, which can be interpreted as the result of competition. Below we give several examples of such a distribution.

Studying the changes in the species composition of birds in the Peruvian Andes as they climbed the mountains, J. Terborgh (Terborgh, 1971) found that species of the same genus very clearly replace each other, and the boundaries of distribution are often not associated with the vertical zonality of vegetation, but are probably determined by only competition between closely related species. The scheme (Fig. 57), borrowed from the work of J. Terborgh, shows that the more species of the same genus are found in the entire surveyed range of altitudes, the smaller the interval of altitudes falls on average per species. So, if from a height of 1000 to a height of 3400 m there are two representatives of the same genus, then each has an interval of 1200 m, and if three species of the same genus live in the same range of heights, then each species has an average of 800 m. distribution clearly indicates competition, and it can hardly be explained without taking into account interspecies interactions (MacArthur, 1972). Important additional evidence for the presence of competition in the case described by J. Terborgh was obtained from a study of the vertical distribution of birds, conducted with the participation of the same author (Terborgh, Weske, 1975) in the Andes, but not on the main ridge, but on a small isolated mountain range, located 100 km from it. The number of species living here was significantly less than on the ridge, but the same species were found in a greater range of altitudes, indicating that it is competition rather than abiotic factors that limits their distribution on the main ridge.

Many examples of interspecific competition are provided by the island fauna (Mayr, 1968), whose representatives often show mutually exclusive distribution, although they live side by side on the mainland. So, M. Radovanovic (Radovanovic, 1959; cited by Mayr, 1968), having studied the distribution of lizards of the genus Lacerta on 46 islands in the Mediterranean off the coast of Yugoslavia, found out that on 28 islands only Lacerta melisellensis, and on the rest - only Lacerta sicula. There is not a single island where both species would live together.

In more rare cases, researchers could directly observe the expansion of the area of ​​distribution of one species, accompanied by the disappearance or reduction in the number of another species in this area, which is its potential competitor. So, from the end of the 19th century to the middle of the 20th century. in Europe, a sharp reduction in the range of broad-toed crayfish was noticed (Astacus astacus) and the corresponding extension to the northwest of the range of a closely related species - long-clawed crayfish (Astacus lepiodactylus), captured the entire Volga basin, and then penetrated into the basin of the Neva and the Seversky Donets (Birshtein, Vinogradov, 1934). At present, both species are found in the Baltic States and Belarus, however, the cases of their presence in the same water body are very rare (Tsukerzis, 1970). The mechanism of displacement of one species by another is not clear, with the exception of those few cases when the long-clawed crayfish was specially launched into those water bodies where the broad-clawed crayfish died during the epizootic of "crayfish plague" - a fungal disease that can completely destroy the crayfish population. It is likely that the successful expansion of the range A. lepiodactylus also contributed to the fact that, compared with A. astacus it grows faster, is more fertile and has the ability to feed around the clock, and not just at night, like a broad-toed crayfish.

A sharp decline in the range of the common squirrel has been observed in the British Isles (Sciurus vulgaris) after the importation from North America of a closely related species of the Carolina squirrel (Sciurus carolinensis), although the nature of competitive displacement has remained unknown. Island species are particularly affected by mainland invaders, who tend to be more competitive. As noted by E. Mayr (1968), most of the bird species that have disappeared over the past 200 years have been insular.

Obviously, an increase in the area of ​​distribution of one species, coinciding with a simultaneous reduction in the area of ​​distribution of another ecologically close species, does not necessarily have to be a consequence of competition. Other biotic factors, such as predatory activity, availability of prey, or changes in abiotic conditions, can also influence such a shift in habitat boundaries. Thus, as an example of competitive displacement, the change in the distribution of two species of hares in Newfoundland was considered earlier: the polar hare (Lepus arcticus) n American hare (Lepus americanus). More than a hundred years ago, only the polar hare lived on the island, which inhabited a wide variety of biotopes, both in the mountains and in the forest valleys. The white hare, brought to the island at the end of the last century, spread through forest valleys, while the polar hare began to be found only in mountainous treeless regions. A simple hypothesis was proposed for the competitive displacement of one species by another, but then it turned out (Bergerud, 1967) that the predator, the lynx, is to blame for the disappearance of the polar hare from forest areas. (lynx lynx), the number of which increased sharply after the introduction of the white hare to the island. An indirect argument in favor of the fact that the pressure of predators played a decisive role in this case is the disappearance of the polar hare from those areas where the mountain hare did not penetrate, but which, due to the nature of the vegetation, are convenient for chasing hares at a trot. Thus, the hypothesis of competitive exclusion in this case, although not completely rejected, should have given way to a hypothesis that takes into account the relationship of three species: two potential competitors and one predator.

Coexistence of competing species. Models of dynamics determined by the concentration of resources

If there are very few reliably proven cases of competitive displacement of one species by another in natural conditions, and there are endless discussions about the importance of competition as a factor determining the dynamics of populations and communities, then in themselves numerous facts of the coexistence of ecologically close and therefore most likely competing species do not raise doubts. . So, we have already mentioned the “plankton paradox” above, but with no less reason we can talk about the “meadow paradox”, since a number of species of herbaceous plants, limited by light, moisture and the same set of mineral nutrition elements, grow side by side. in one place, although they are in competitive relations.

In principle, the coexistence of competing species (i.e., non-observance of the Gause law) can be explained by the following circumstances: 1) populations of different species are limited by different resources; 2) the predator predominantly eats out a stronger competitor; 3) the competitive advantage of species varies depending on the volatility of external conditions (i.e., competitive exclusion each time does not reach the end, giving way to a period favorable for the species that was previously ousted); 4) populations of different species are actually separated in space-time, and what appears to the observer as one habitat, from the point of view of the studied organisms, contains a whole set of different habitats.

In order to explain the coexistence of species that compete for a limited number of resources, it is necessary to at least briefly consider the model of the dynamics of populations that are limited in their development by the amount of available resources. This model is based on the already mentioned above idea of ​​the so-called threshold resource concentration R*, i.e., that minimum concentration at which the birth rate is exactly balanced by the death rate (see Fig. 44), and the population remains stationary. Obviously, for different species that depend on the same resource, the values ​​of threshold concentrations may not coincide, but if there is a lot of resource in the environment, then both species grow at maximum rates, and the species that has the largest difference in fertility at a given concentration grows faster. and mortality (i.e. the value b-d). It is obvious, however, that in the natural setting, as the number of organisms consuming a given resource increases, its concentration in the environment decreases, and when it reaches the threshold value for a given type of organisms, the population begins to fall. As a result of the competition of two species for one resource, the one for which the threshold concentration of the resource is lower wins.

Now consider a model with two resources whose concentrations in the medium R1 And R2 put on two orthogonal axes (Fig. 58). In the coordinate space of these resources, we draw a line corresponding to those values ​​of the concentrations of the first and second resources at which the population keeps its size constant ( dN/Ndt = 0). This line, called the zero growth isocline, actually corresponds to the threshold combinations of concentrations of the first and second resources for a given species. If the points corresponding to the concentrations of resources observed in the environment lie closer to the origin of coordinates from this line, then the population size at the given values ​​of concentrations will decrease. If they lie beyond the isocline, then the population will increase.

Note that the isocline straight line in this graph is drawn only for simplicity. This case corresponds to the interchangeability of resources, i.e., the ability of a species to successfully exist, consuming only one of the resources or being content with some combination of them. In fact, the isocline can be concave (complementarity of resources) in those cases when, eating a mixture of different components, the body consumes them in total less than when feeding each of these components separately, and convex, for example, when the action of toxic substances is synergistic consumed with different food components. Please note that in order to maintain a constant number of one species (Fig. 58, A) much more of the second resource is required than the first, but a different kind (Fig. 58, b) can be a more efficient consumer of the second resource, which it needs correspondingly less than the first one.

Now let's try to draw an isocline of zero growth for the second type on the same graph. It is obvious that if the isocline of type B passes closer to the origin of coordinates than the isocline of type A (Fig. 58, b), then type B will be the winner in the competition, since it will “bring” the concentration of both resources to such a low level at which the stationary population type A cannot exist. If the isocline of type B passes further from the origin of coordinates than the isocline of type A, then type A will be the winner in the competition (Fig. 58, d). If the isoclines of two species intersect, then at a certain ratio of resources in the environment, the species can coexist, and at another, one species may be crowded out by another. For example, in the situation depicted in Fig. 58, d, with a high concentration of the second resource and a low concentration of the first, species A has a competitive advantage, and with a high concentration of the first resource and a low concentration of the second, species B has an advantage.

The above example corresponded to resources that are completely interchangeable. For most organisms, however, there are a number of irreplaceable resources. So, for example, no matter how well a plant is provided with nitrogen, it will not be able to grow and develop if there is no phosphorus in its nutrient medium. In the coordinate axes of two resources, the isocline of zero population growth, bounded by such "two resources, will be depicted by a line curved at a right angle, i.e., so that it turns out to consist of two branches parallel to the axes of the graph (Fig. 59, A). The position of each branch corresponds to the threshold concentration of the first or second resource. If two species compete for two irreplaceable resources, then, just as in the case of interchangeable resources, different options for the location relative to each other of the isoclines of zero increment of these species are possible. Obviously, in the situation depicted in Fig. 59, b, the winner will be type A, and in the one shown in fig. 59, b - view C. When crossing the isoclines (Fig. 59, G) coexistence of both species can be achieved, since different resources are limiting for each of them.

The latter case is also experimentally confirmed. Thus, David Tilman (Tilman, 1982), who made a great contribution to the development of modern ideas about competition for resources, conducted a series of experiments with two species of planktonic diatoms Asterionella formosa And Cyclotella meneghiniapa and on the basis of the data obtained, he constructed zero growth isoclines for them depending on the concentration of two irreplaceable resources - phosphorus and silicon (Fig. 60).

Within the framework of this model, it is relatively easy to explain the coexistence of different species if they are limited by different resources. However, the very concept of “different resources” needs to be clarified. So, probably, everyone will agree that different types of plants for phytophagous animals can be considered as different resources. With somewhat lesser grounds, but, apparently, one can also say that different parts of one plant can be interpreted as different resources. However, the amount of mineral nutrients needed by plants along with light and moisture is very limited. In any case, it is much less than the number of planktonic algae species living within a small volume of water (remember the "plankton paradox"), or the number of herbaceous plant species growing in one meadow. An attempt to explain the coexistence of many species competing for a small number of common resources was undertaken by D. Tilman (Tilman, 1982). To clarify the essence of his reasoning, it is necessary to introduce some complications into the model described above.

Let's start with the fact that all the previous reasoning was based on the assumption of stable concentrations of resources. It is clear, however, that in reality the resources, like the populations consuming them, are in constant dynamics or, in any case, in a state of dynamic equilibrium, in which the consumption of the resource is balanced by its influx into the environment. If we imagine that consumers can be withdrawn from the environment, then, obviously, some higher concentrations of limiting resources will be established in it. The point corresponding to the concentration of resources in the absence of consumption, D. Tilman proposed to call the supply point. In fact, we have already implicitly used this notion when discussing the models depicted in Fig. 58-59, and talked about one or another concentration of resources observed in the environment. On fig. 61 in the space of two irreplaceable resources, a supply point is plotted (its coordinates S1, S2) and zero growth isocline for one species. At every point on a given isocline, fertility is, by definition, equal to mortality, but this does not mean that the ratio in consumption of two resources is necessarily exactly equal to their ratio when they enter the environment. From each point we can draw a consumption vector WITH, showing the direction in which the population tends to shift the threshold concentration, and the supply vector u, directed to the supply point and showing the ratio of resources that would be established in the environment with some weakening of its consumption by this population. The consumption vector and the supply vector can be directed in strictly opposite directions (at an angle of 180°): in this case, the corresponding point on the isocline will be called the resource equilibrium point (point E in fig. 61). At other points of the isocline, the consumption vector and the supply vector may be at an angle less than 180°: such a ratio of resources will be non-equilibrium.

Rice. 61. Isocline of zero population growth in terms of irreplaceable resources (according to Tilman, 1982)

Rice. 62. Isoclines of two types, limited by two irreplaceable resources: C A and C B - consumption vectors (according to Tilman, 1982)

Rice. 63. Isoclines of four types (a, b, c, d), limited by two resources. Each of the circles shows a certain variability in the quantitative ratio of these resources in the environment (according to Tilman, 1982)

In the case of the intersection of isoclines of two species competing for two independent resources, the resource equilibrium point is just the intersection point of the isoclines. On fig. 62 shows the consumption vectors (and the supply vectors that continue them) emanating from the equilibrium point. The coexistence of species in this case is stable, since each of the competing species consumes to a greater extent the resource that more restricts the growth of its own population. In particular, in fig. 62 type A consumes the second resource more, and type B - the first. If the situation were reversed, then the coexistence of species would be unstable. Referring to the diagram shown in Fig. 62, where the numbers indicate individual areas bounded by isoclines and vectors, then in the area 1 neither species A nor species B can exist, in the region 2 A can exist, but B cannot; and areas 6 the opposite situation is observed - B can exist, but A cannot; in area 4 both species successfully coexist; in area 3 A competitively displaces B, and in the region 5 B competitively displaces A.

Instead of two species in the space of two resources, we can draw isoclines of a number of species and, from the intersection points of these isoclines, draw supply vectors that limit the areas in which the coexistence of each pair of species is possible (Fig. 63). At different points in this space, one species, two species, or none can live. In other words, with a precisely defined quantitative ratio of two resources, the principle of competitive exclusion is strictly observed in each specific case: the number of coexisting species does not exceed the number of limiting resources. But if we turn from an idealized model to nature, we will find that even closely located points in any real space of any habitat (both terrestrial and aquatic) differ quite strongly in the quantitative ratio of limiting resources. In addition, the ratio determined for any point can vary greatly over time. So, for example, a very detailed study of the distribution of nitrogen content in the soil of a 12 × 12 m plot by D. Tilman showed a variation of 42%, and the variation in magnesium content in the same plot reached 100%. Spatio-temporal variability in the flow of resources into the environment in fig. 63 can be depicted as a circle of a certain diameter. As can be seen from the diagram, if this circle is placed in the area of ​​high concentrations, then no more than two species can coexist with such variations, but if the same circle is placed in the area of ​​low values, then it can cover the area of ​​coexistence of a number of species at once. In other words, at very low concentrations of limiting resources, even their very slight variability from one point in space to another or from one point in time to another is enough to ensure the real possibility of the coexistence of a large number of species at once (in any case, much more than the number of limiting resources ). Another interesting conclusion follows from this: when the environment is enriched with resources, we have the right to expect a decrease in species diversity. Such a reduction in the number of species and an increase in the numerical predominance of a few species are indeed observed both in the aquatic environment (the phenomenon of eutrophication) and in the terrestrial environment (depletion of the species composition of meadows with long-term fertilization).

Conclusion

In nature, any population of a species of organisms enters into a network of relationships with populations of other species: Predator-prey (or resource-consumer) relations and competitive relations are one of the most important in the life of any organism and at the same time one of the most studied. With an increase in the number of prey, both a functional response of the predator (i.e., an increase in the number of prey consumed per unit of time by one individual of the predator) and a numerical one (i.e., an increase in the size of the predator population) are observed. Owing to the ability of predators to react functionally and numerically, their pressure on the prey population acts as a density-dependent factor and therefore has a regulatory effect.

According to the theory developed by mathematicians, the system of interconnected predator and prey populations should most likely demonstrate an oscillatory regime, but even under laboratory conditions it is practically very difficult to obtain stable predator-prey oscillations. In those cases where this is possible, the researchers, as a rule, limit the amount of food for the prey or create a complex heterogeneous habitat in which the prey and predator can migrate, and the prey dispersal rate is slightly higher than the predator dispersal rate. Under natural conditions, we usually see only the follow- ing of the number of predators to prey fluctuations determined by other factors that are not directly related to the impact of this predator.

The evolution of the predator and the evolution of the prey are always closely related. One of the possible ways in evolution to protect the prey from the pressure of predators is to increase the birth rate (compensating for the corresponding increase in mortality from the predator). Other possible ways: this is a strategy of avoiding encounters with a predator or a strategy of developing morphological, physiological and biochemical means of protection against it. Both of these strategies, aimed at directly reducing mortality from a predator, are associated with certain expenses for the victim, which ultimately translate into a decrease in the birth rate. The evolution of a predator is aimed at increasing its own birth rate and (or) reducing mortality, which is almost always associated with an increase in the efficiency of using prey.

Competitive relations between populations of different species arise when they are in dire need of one resource that is available in insufficient quantities. Competition can proceed according to the type of exploitation, that is, the simple use of a scarce resource, or according to the type of interference, in which individuals of one species interfere with individuals of another in the use of common resources.

There is a long tradition in ecology of the theoretical study of competition. According to the Volterra-Lotka mathematical model, later developed and experimentally confirmed by G.F. Gause, two species competing for one resource, as a rule, cannot coexist stably in a homogeneous environment, and the outcome of competition is determined by the ratio of the intensity of self-limitation of each of the populations and their mutual limitation . This rule, also known as Gause's law, or the principle of competitive exclusion, has undergone a certain development as a result of a comprehensive study by theorists and experimenters. In its modern formulation, it states that the number of species coexisting indefinitely in constant conditions of a homogeneous habitat cannot exceed the number of density-dependent factors that limit the development of their populations.

Gause's law continues to hold heuristic value for naturalists studying competition in nature. Direct evidence of the importance of the role of interspecific competition in nature is immeasurably more difficult to obtain than in the laboratory. Therefore, as a rule, the significance of competition as a factor that determines the dynamics and distribution of natural populations is judged by the totality of indirect evidence.

In some cases, the number of coexisting species competing for common resources limiting their development is clearly greater than the number of such resources (for example, a community of planktonic algae or a community of meadow plants), which contradicts the Gause law. This contradiction is removed, however, by a theory that takes into account the spatial and temporal variability in the provision of competing species with limiting resources.

In Russian, the word "ecology" was first mentioned, apparently, in a brief synopsis of "General Morphology" by E. Haeckel - a small book published in 1868 under the editorship of I. I. Mechnikov.

Now, however, we are beginning to realize that, perhaps, there is no point in trying to develop ecology and biology in general along the lines of physics. It is possible that the biology of the future will be closer to the humanities. In any case, "fitness" - one of the central concepts in Darwinism (and this is so far the only fairly general eco-evolutionary theory) - belongs to the field of semantic information (Zarenkov, 1984).

The most species-rich group of organisms on earth are insects. There are more species of insects than all other animal and plant species combined. Their total number remains unknown, since most insect species living in the tropics have not yet been described. Until recently, it was believed that there were 3-5 million species of insects, but in recent years data have appeared (May, 1988) indicating that this figure should be increased, perhaps by an order of magnitude, i.e. the number of insect species on Earth not less than 30 million. The basis for this reassessment was, in particular, the results of a survey of the crowns of tropical trees. So, using the fumigation technique to expel insects from the crowns, it was possible to show that 19 specimens. one species of tropical evergreen tree Geuhea seemanni in Panama, there were 1,100 species of beetles alone.

The above definition, as the author points out, is a slightly modified definition of ecology proposed by the Australian researcher G. Andrewartha (Andrewartha. 1961), who, in turn, proceeded from ideas developed back in the 20s. C. Elton (1934; Elton, 1927).

A similar situation was observed, however, in physics. As Weiskopf (1977) noted, the progress made by this science in modern times is associated with the abandonment of attempts to establish at once the whole truth and explain the entire universe. Instead of asking general questions and getting specific answers, scientists began to ask more specific questions, but, surprisingly, they got more general answers.

Note that the expressions “sufficiently perfect” or “sufficiently adapted” do not mean at all that this species is adapted in the best way, and there is nowhere for it to improve further. It also does not follow from what has been said that each species lives in nature under the most optimal conditions. It often happens that from the most optimal (according to abiotic conditions) parts of its potential range, a species is forced out by competitors or predators. It is enough to refer at least to the above example with St. Chrysolina.

In the English-language literature devoted to the evolutionary aspects of ecology, the English proverb “Jack of all trades is a master of none” is very often quoted, which can be roughly translated into Russian as follows: “He who undertakes to do any job does not do any of them well ".

Taxonomic specialists notice (Skvortsov, 1988) that certain names of taxonomic categories are rather proper names, rather than common nouns. For example, when we say “class of monocots” or “class of reptiles”, we first of all imagine monocots and reptiles, and not a certain “class in general” - a conventional unit of taxonomists who agreed that classes are divided into orders, and united into types.

Among domestic scientists, this point of view was defended by S. S. Schwartz (1969). A. V. Yablokov (1987), who in his book “Population Biology” defines a population as “... a minimal self-reproducing group of individuals of the same species, inhabiting a certain space for an evolutionary long time, forming an independent genetic system and forming its own ecological space” (p. 150). Explaining his definition, A. V. Yablokov emphasizes that “... a population is always a fairly large group of individuals, over a large number of generations, to a high degree isolated from other similar groups of individuals” (p. 151).

Clones are usually called groups of individuals descended from one ancestral form by vegetative or parthenogenetic reproduction and therefore are very close relatives. Ecologists often use clones of algae, protozoa, rotifers and other organisms in their experiments.

Phytocenologists often adhere to this point of view with particular strictness. Instead of the term "population", they prefer to use the term "coenopopulation", thereby emphasizing that this is not just a collection of plants of a certain species, but a collection that is part of a specific cenosis (=community).

N. P. Naumov in the 1960s consistently defended a “soft” definition of a population, rightly emphasizing that the very disputes about the possibility or impossibility of considering this or that grouping as a population are objective in nature, since they reflect the natural hierarchical structure of the population. In our opinion, quite rightly, N.P. Naumov (1965, p. 626) believed that population dynamics is “a phenomenon that unfolds not only in time, but also in space.”

Estimating the total population size is especially important for endangered species of animals and plants listed in the Red Book. The question of what the minimum allowable size of these populations can be becomes a purely practical one.

Specialists studying the technique of measuring the spatial distribution recommend using the indicator σ 2 / T only in those cases when, as the mean increases (which is achieved by using larger areas), the variance grows linearly. In other cases, other indicators of spatial aggregation are used (Romanovsky, 1979).

We emphasize that in this example we mean the dry weight of food (wet weight can be 10 times more). All figures are taken from the generalizing work of B. D. Abaturov and V. N. Lopatin (1987).

Demecology is a scientific discipline that considers the variety of relationships between living organisms that are part of different populations. One form of such interaction is interspecies competition. In this article, we will consider its features, the patterns of the emergence of a struggle for territory, food and other abiotic factors in organisms living in natural and artificial biogeocinoses.

View and its ecological characteristics

In the course of historical development, biological taxa (groups that have some commonality) adapt to the abiotic and biotic factors of nature. The first include climate, the chemical composition of the soil, water and air, etc., and the second - the impact of the life of some species on others.

Individuals of the same species settle unevenly in certain areas of biotopes. Their clusters are called populations. Communities of one species are in constant contact with populations of other species. This determines its position in the biogeocenosis, which is called

Individuals of these species entered into competition with each other for food (flour) and were predators (they ate beetles of another species).

Under artificial conditions of the experiment, temperature and humidity varied. With them, the probability of the dominance of communities of one or the other species changed. After a certain time interval, individuals of only one species were found in the artificial environment (a box of flour), while individuals of the other completely disappeared.

Operational competition

It arises as a result of the purposeful struggle of organisms of various species for an abiotic factor that is at a minimum: food, territory. An example of this form of ecological interaction is the feeding of birds belonging to different species on the same tree, but in its different tiers.

Thus, interspecific competition is in biology such a type of interaction between organisms that leads to:

• to a cardinal division of populations of various species according to mismatched ecological niches;
• to the expulsion of one less plastic species from biogeocinosis;
• to the complete elimanation of individuals in the population of a competing taxon.

Ecological niche and its limitations associated with interspecific competition

Ecological studies have established that biogeocinoses consist of as many ecological niches as there are species living in an ecosystem. The spatially closer the ecological niches of communities of important taxa in the biotope, the more fierce their struggle for better environmental conditions:

• territory;
• feed base;
• population residence time.

The decrease in environmental pressure in the biotope occurs as follows:

• layering in mixed forest;
• different habitats for larvae and adults. So, in dragonflies, naiads live on aquatic plants, and adults have mastered the air environment; in the May beetle, the larvae live in the upper layers of the soil, and adult insects live in the ground-air space.

All these phenomena characterize such a concept as interspecific competition. The examples of animals and plants given above confirm this.

Results of interspecific competition

We consider a widespread phenomenon in wildlife, characterized as interspecific competition. Examples - biology and ecology (as its section) - present this process to us both in the environment of organisms belonging to the kingdoms of fungi and plants, and in the animal kingdom.

The results of interspecific competition include the coexistence and substitution of species, as well as ecological differentiation. The first phenomenon is extended in time, and related species in the ecosystem do not increase their numbers, since there is a specific factor that affects the reproduction of the population. Substitution of species, based on the laws of competitive exclusion, is an extreme form of pressure of a more plastic and sertile species, which inevitably entails the death of an individual - a competitor.

Ecological differentiation (divergence) leads to the formation of little changing, highly specialized species. They are adapted to those areas of the common range where they have advantages (in terms and forms of reproduction, nutrition).

In the process of differentiation, both competing species reduce their hereditary variability and tend to a more conservative gene pool. This is explained by the fact that in such communities the stabilizing form of natural selection will dominate over its driving and disruptive types.

intraspecific competition

This is competition between members of one or more populations of a species. Goes for resources, intra-group dominance, females/males, etc.

Interspecific competition

This is competition between populations of different types of non-adjacent trophic levels in a biocenosis. It is due to the fact that representatives of different species jointly use the same resources, which are usually limited. Resources can be both food (for example, the same types of prey for predators or plants - for phytophages), and of another kind, for example, the availability of places for breeding, shelters for protection from enemies, etc. Species can also compete for dominance in the ecosystem. There are two forms of competitive interactions: direct competition (interference) And indirect (exploitation). With direct competition between populations of species in a biocenosis, antagonistic relationships (antibiosis) develop evolutionarily, expressed by various types of mutual oppression (fights, blocking access to a resource, allelopathy, etc.). In case of indirect competition, one of the species monopolizes a resource or habitat, thus worsening the conditions for the existence of a competitive species in a similar ecological niche.

Both evolutionarily (taxonomically) close species and representatives of very distant groups can compete in nature. For example, ground squirrels in the dry steppe eat up to 40% of plant growth. This means that pastures can support fewer saigas or sheep. And during the years of mass reproduction of locusts, neither gophers nor sheep have enough food.

see also

Literature

• Shilov I. A. Ecology. - M.: Higher school, 1997. - 512 p.
• Ecology. Textbook / ed. A. K. Akhlebinina, V. I. Sivoglazov. - Bustard, 2004. - (1C: School).

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- (from lat. concurrere "collide", "compete") struggle, rivalry in any area. Contents 1 In biology 2 In economics 3 In law ... Wikipedia

This term has other meanings, see Antagonism. This article lacks links to sources of information. Information must be verifiable, otherwise it may be questioned and ud ... Wikipedia

Elimination (from Latin elimino I take out the threshold, remove) in biology is the process of extinction of individuals, groups of individuals or entire populations, as well as their elimination from reproduction as a result of various environmental factors. Among these ... Wikipedia

Axial root, underground vegetative organ of higher plants, with unlimited growth in length and positive geotropism. The root fixes the plant in the soil and ensures the absorption and conduction of water with dissolved ... ... Wikipedia

- (also top predators, superpredators) the general name for a group of organisms that occupy the top position in the food chain (if we consider only predators) (that is, their numbers are not regulated by other predators). Contents 1 General ... ... Wikipedia

Antibiosis is a form of relationship in which both interacting species or one of them experience a harmful, overwhelming life activity, influence from the other.

Neutralism is a form of relationship in which there are no direct interactions between species and they do not have a noticeable effect on each other.

In nature, such relationships between organisms are not easy to detect, since the complexity of biocenotic relationships leads to the fact that most species at least indirectly influence each other.

For example, many forest animals (shrews, small rodents, squirrels, woodpeckers) are not directly related as part of the biocenosis, but all depend on the supply of coniferous seeds and on this basis they indirectly influence each other.

Neutrality relationships are characteristic of species-rich communities.

Competition (- -).

Competition(from lat. concurro - collide, knock) - this is a form of relationship that is observed between organisms when they share the resources of the environment, the number of which is not enough for all consumers.

Competitive relationships play an extremely important role in the formation of species composition, the distribution of species in space, and the regulation of the number of species in a community.

Distinguish intraspecific and interspecific competition.

Intraspecific competition - it is a struggle for the same environmental resources between individuals of the same species.

Intraspecific competition is the most important form of the struggle for existence, which fundamentally increases the intensity of natural selection.

At the same time, interspecific competition manifests itself the more sharply, the more similar the ecological needs of competitors are.

There are two forms of interspecific competitive relations: direct and indirect competition.

Direct (active) competition - suppression of one species by another.

With direct competition between species, directed antagonistic relations develop, which are expressed in various forms of mutual oppression (fights, blocking access to a resource, chemical suppression of a competitor, etc.).

However, many birds and animals aggression is the main form of relationship that determines the competitive displacement of one species by another in the process of struggle for common resources.

For example:

- in forest biocenoses, competition between wood mice and bank voles leads to regular changes in the habitats of these species. In years with increased numbers, wood mice populate various biotopes, displacing bank voles to less favorable places. And, conversely, voles, with their numerical superiority, are widely settled in places from which they were previously driven out by mice. At the same time, it was shown that the mechanism of competitive division of habitats is based on aggressive interactions;

- sea urchins that settled in coastal algae physically eliminate other consumers of this food from their pastures. Experiments with the removal of sea urchins have shown that algae thickets are immediately populated by other animal species;

- in European human settlements, the gray rat, as a larger and more aggressive one, completely replaced another species - the black rat, which now lives in the steppe and desert regions.

Indirect (passive) competition - consumption of environmental resources required by both species.

Indirect competition is expressed in the fact that one of the species worsens the conditions for the existence of another species with similar ecological requirements, without exerting direct forms of influence on the competitor.

With indirect competition, success in competition is determined by the biological characteristics of the species: reproduction intensity, growth rate, population density, intensity of resource use, etc.

For example:

- broad-toed and narrow-toed crayfish cannot co-exist in the same reservoir. Usually the winner is the narrow-toed crayfish, as the most prolific and adapted to modern conditions of life;

- in human settlements, the small red Prussian cockroach replaced the larger black cockroach only because it is more prolific and better adapted to the specific conditions of human habitation.

A classic example of indirect interspecific competition are laboratory experiments conducted by the Russian scientist G.F. Gause, according to the joint content of two types of ciliates with a similar nature of nutrition.

It turned out that when two types of ciliates were grown together, after some time only one of them remained in the nutrient medium. At the same time, ciliates of one species did not attack individuals of another species and did not emit harmful substances to suppress a competitor. This was explained by the fact that these species differed in unequal growth rates and in the competition for food, the faster growing and reproducing species won.

Model experiments carried out by G.F. Gause, led him to formulate the well-known competitive exclusion principle (Gause theorem):

Two ecologically identical species cannot co-exist in the same area, i.e. cannot occupy exactly the same ecological niche. Such species must necessarily be separated in space or time.

From this principle follows, that cohabitation in the same territory of closely related species is possible in those cases when they differ in their ecological requirements, i.e. occupy different ecological niches.

For example:

- insectivorous birds avoid competition with each other due to different places for searching for food: on tree trunks, in bushes, on stumps, on large or small branches, etc.;

- hawks and owls, which eat roughly the same animals, avoid competition by hunting at different times of the day: hawks hunt during the day, and owls hunt at night.

Thus, interspecific competition that occurs between closely related species can have two consequences:

- displacement of one species by another;

- different ecological specialization of species, allowing them to exist together.

Interspecific competition

Competition between species is extremely widespread in nature and affects almost everyone, since it is rare that a species does not experience at least a little pressure from individuals of other species. However, does ecology consider interspecies competition in a specific, narrower sense? only as mutually negative relationships of species occupying a similar ecological niche.

Forms of manifestation of interspecies competition can be very diverse: from tough struggle to almost peaceful coexistence. But, as a rule, of two species with the same ecological needs, one necessarily displaces the other.

Here are some examples of competition between ecologically close species.

In Europe, in human settlements, did the gray rat completely replace another species of the same genus? a black rat that now lives in the steppe and desert regions. The gray rat is larger, more aggressive, swims better, so it managed to win. In Russia, the relatively small red Prussian cockroach completely replaced the larger black cockroach only because it was able to better adapt to the specific conditions of a human dwelling.

Shoots of spruce develop well under the protection of pines, birches, aspens, but then, with the growth of spruce crowns, shoots of light-loving species die. Weeds oppress cultivated plants as a result of the interception of soil moisture and mineral nutrients, as well as as a result of shading and the release of toxic compounds. In Australia, the common bee, introduced from Europe, has supplanted the small, stingless native bee.

Interspecific competition can be demonstrated in simple laboratory experiments. So, in the studies of the Russian scientist G.F. Gause cultures of two types of ciliates-shoes with a similar nature of nutrition were placed separately and together in vessels with hay infusion. Each species, placed separately, successfully multiplied, reaching the optimal abundance. However, when living together, the number of one of the species gradually decreased, and its individuals disappeared from the infusion, while the ciliates of the second species survived. It was concluded that long-term coexistence of species with close ecological requirements is impossible. Is this conclusion named? competitive exclusion rule.

In another experiment, the researchers looked at the effect of temperature and humidity on the outcome of interspecific competition between two flour beetle species. Several individuals of one and another species were placed in vessels with flour (at a certain combination of heat and moisture). Here the beetles began to multiply, but after a while only individuals of one species remained. It is noteworthy that at high rates of heat and moisture, one species won, but at low? another.

Consequently, the outcome of competition depends not only on the properties of the interacting species, but also on the conditions in which the competition takes place. Depending on the conditions prevailing in a particular habitat, either one or the other species may be the winner of the competition.

In some cases, this leads to the coexistence of competing species. After all, heat and humidity, like other environmental factors, are by no means evenly distributed in nature. Even within a small area (forest, field or other habitat), you can find zones that differ in microclimate. In this variety of conditions, each species develops the place where it is guaranteed to survive.

The main resource that is the subject of competition for plant organisms is light. Of two similar plant species coexisting in the same habitat, the advantage is achieved by the species that is able to enter the upper, better illuminated tier earlier. This can be facilitated, on the one hand, by rapid growth and early achievement of foliage, on the other? the presence of long petioles and high planted leaves. Does rapid growth and early leafing provide advantages in the early growing season, long petioles and high-set leaves? at the adult stage.

Observations on the populations of two cohabiting clover species (one of which has advantages in growth rate, and the other in the length of leaf petioles) show that in mixed herbage each species suppresses the development of the other. Nevertheless, both of them are able to complete their life cycle and produce seeds, that is, there is no complete displacement of one species by another. Both species, despite strong competition for light, can coexist. This is due to the fact that the stages of development, when the growth rate of these species reaches a maximum (and the need for light is especially high), do not coincide in time.

Thus, only those competing species coexist in the community that have adapted to at least slightly differ in ecological requirements. So, in the African savannas, ungulates use pasture food in different ways: zebras cut off the tops of grasses, wildebeests eat plants of certain species, gazelles pluck only the lower grasses, and topi antelopes feed on tall stems.

In our country, insectivorous birds feeding on trees avoid competition with each other due to the different nature of the search for prey on different parts of the tree.

Competition as an environmental factor

Competitive relations play an extremely important role in the formation of the species composition and regulation of the number of species in the community.

It is clear that strong competition can only be found between species occupying similar ecological niches. The concept of "ecological niche" reflects not so much the physical position of a species in an ecosystem as a functional one, characterizing the specialization ("profession") of these organisms in nature. Therefore, severe competition can only occur between related species.

Ecologists know that organisms that lead a similar way of life, have a similar structure, do not live in the same places. And if they live nearby, they use different resources and are active at different times. Their ecological niches seem to diverge in time or space.

Is the divergence of ecological niches when related species coexisting well illustrated by the example of two species of marine fish-eating birds? cormorants and long-nosed cormorants, which usually feed in the same waters and nest in the neighborhood. It was possible to find out that the composition of the food of these birds differs significantly: the long-nosed cormorant catches fish swimming in the upper layers of the water, while the great cormorant catches it mainly at the bottom, where flounders, bottom invertebrates, such as shrimps, predominate.

Competition has a huge impact on the distribution of closely related species, although often only indirect evidence indicates this. Species with very similar needs usually live in different geographical areas or different habitats in the same area. Or they avoid competition in some other way, such as differences in food or differences in daily or even seasonal activity.

The ecological action of natural selection seems to be aimed at eliminating or preventing a prolonged confrontation between species with a similar way of life. The ecological separation of closely related species is fixed in the course of evolution. In Central Europe, for example, there are five closely related species of tits that are isolated from each other due to differences in habitat, sometimes in feeding areas and size of prey. Ecological differences are also reflected in a number of small details of the external structure, in particular in changes in the length and thickness of the beak. Changes in the structure of organisms that accompany the processes of divergence of their ecological niches suggest that interspecific competition is one of the most important factors in evolutionary transformations.

Interspecific competition can play an important role in shaping the appearance of a natural community. Generating and consolidating the diversity of organisms, it helps to increase the resilience of communities, more efficient use of available resources...