Competition between different types of predators for food. What is interspecific competition? Examples. Intraspecific struggle for existence

Competition is the competition between organisms of the same trophic level (between plants, between phytophages, between predators, etc.) for the consumption of a resource available in limited quantities.

Competition for the consumption of resources plays a special role during critical periods of their scarcity (for example, between plants for water during a drought or predators for prey in an unfavorable year).

There are no fundamental differences between interspecific and intraspecific (intrapopulation) competition. There are cases where intraspecific competition is more intense than interspecific competition, and vice versa. Moreover, the intensity of competition within and between populations can change under different conditions. If conditions are unfavorable for one of the species, then competition between its individuals may increase. In this case, it may be displaced (or more often, displaced) by a species for which these conditions turned out to be more suitable.

However, in multispecies communities, “dueling” pairs most often do not form, and competition is diffuse: many species simultaneously compete for one or several environmental factors. “Duelists” can only be mass species of plants that share the same resource (for example, trees - linden and oak, pine and spruce, etc.).

Plants may compete for light, for soil resources, and for pollinators. On soils rich in mineral nutrition resources and moisture, dense, closed plant communities are formed, where light is the limiting factor for which plants compete.

When competing for pollinators, the species that is more attractive to the insect wins.

In animals, competition occurs for food resources, for example, herbivores compete for phytomass. In this case, competitors of large ungulates can be insects like locusts or mouse-like rodents that can mass reproduction destroy most of the grass. Predators compete for prey.

Since the amount of food depends not only on environmental conditions, but also on the area where the resource is reproduced, competition for food can develop into competition for space.

As in the relationships between individuals of the same population, competition between species (their populations) can be symmetrical or asymmetrical. Moreover, a situation where environmental conditions are equally favorable for competing species is quite rare, and therefore relations of asymmetric competition arise more often than symmetric ones.

When resources fluctuate, as is usual in nature (moisture or mineral nutrition elements for plants, primary biological production for different types of phytophages, density of prey populations for predators), different competing species alternately gain advantages. This also does not lead to the competitive exclusion of the weaker, but to the coexistence of species that alternately find themselves in a more advantageous and less advantageous situation. At the same time, species can experience deterioration of environmental conditions with a decrease in the level of metabolism or even a transition to a dormant state.

The outcome of the competition is also influenced by the fact that a population that has more individuals and will, accordingly, more actively reproduce “its army” (the so-called mass effect) has a greater chance of winning the competition.

23. Relationship between plant and phytophage and the prey is the predator

RELATIONSHIP "PLANT-PHYTOPHAGE".

The “phytophage-plant” relationship is the first link in the food chain, in which matter and energy accumulated by producers are transferred to consumers.

For plants in equally It is “unprofitable” for them to be eaten completely or not eaten at all. For this reason, in natural ecosystems there is a tendency to form an ecological balance between plants and the phytophages that eat them. For this plant:

– protected from phytophages by spines, forming rosette forms with leaves pressed to the ground, inaccessible to grazing animals;

– protect themselves from complete grazing by biochemical means, producing toxic substances when eating increases, which make them less attractive to phytophages (this is especially typical for slowly growing patients). In many species, when they are eaten, the formation of “unpalatable” substances increases;

– emit odors that repel phytophages.

Protection from phytophages requires significant energy expenditure, and therefore in the relationship “phytophage - plant” tradeoff can be traced: the faster the plant grows (and, accordingly, the faster better conditions for its growth), the better it is eaten, and vice versa, the slower the plant grows, the less attractive it is to phytophages.

At the same time, these means of protection do not ensure complete safety of plants from phytophages, since this would entail a number of undesirable consequences for the plants themselves:

– uneaten steppe grass turns into rags – felt, which worsens the living conditions of plants. The appearance of abundant felt leads to the accumulation of snow, a delay in the onset of plant development in spring and, as a result, to the destruction of the steppe ecosystem. Instead of steppe plants (feather grass, fescue), meadow species and shrubs develop abundantly. At the northern border of the steppe, after this meadow stage, the forest may generally recover;

– in the savanna, a decrease in the consumption of tree shoots by branch-eating animals (antelopes, giraffes, etc.) leads to the fact that their crowns close together. As a result, fires become more frequent and trees do not have time to recover; the savanna degenerates into thickets of bushes.\

In addition, with insufficient consumption of plants by phytophages, space is not freed up for the settlement of new generations of plants.

The “imperfection” of the “phytophage-plant” relationship leads to the fact that short-term outbreaks in the density of phytophage populations and temporary suppression of plant populations occur quite often, followed by a decrease in the density of phytophage populations.

RELATIONSHIP "VICTIM-PREDATOR".

The “predator-prey” relationship represents the links in the process of transfer of matter and energy from phytophages to zoophages or from lower-order predators to higher-order predators.

As in the “plant-phytophage” relationship, a situation in which all victims are eaten by predators, which ultimately leads to their death, is not observed in nature. Ecological balance between predators and prey is maintained by special mechanisms that prevent the complete extermination of the victims. So victims can:

- run away from a predator. In this case, as a result of adaptation, the mobility of both prey and predators increases, which is especially typical for steppe animals that have nowhere to hide from their pursuers (“Tom and Jerry principle”);

– acquire a protective color (“pretend” to be leaves or twigs) or, on the contrary, a bright color (for example, a red color, warning a predator about a bitter taste. It is well known that the color of a hare changes at different times of the year, which allows it to camouflage itself in the leaves in summer, and against a white background in winter snow;

– spread in groups, which makes searching for and catching them more energy-intensive for the predator;

- hide in shelters;

– move to active defense measures (herbivores with horns, spiny fish), sometimes joint (musk oxen can take up “all-round defense” from wolves, etc.).

In turn, predators develop not only the ability to quickly pursue prey, but also a sense of smell, which allows them to determine the location of the prey by smell.

At the same time, they themselves do everything possible to avoid detection of their presence. This explains the cleanliness of small cats, which spend a lot of time toileting and burying excrement to eliminate odors.

With intensive exploitation of phytophagous populations, people often exclude predators from ecosystems (in Great Britain, for example, there are roe deer and deer, but no wolves; in artificial reservoirs where carp and other pond fish are bred, there are no pikes). In this case, the role of the predator is performed by the person himself, removing part of the individuals of the phytophage population.

In this case, interspecific competition manifests itself 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 is the suppression of one species by another.

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

Moreover, in 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 inhabit a variety of biotopes, displacing bank voles to less favorable places. And, conversely, voles, with their numerical superiority, widely settle in places from which they were previously driven out by mice. It was shown that the mechanism of competitive habitat division is based on aggressive interactions;

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

* In European human settlements, the gray rat, being larger and more aggressive, completely replaced another species - the black rat, which now lives in steppe and desert areas.

Indirect (passive) competition is the consumption of environmental resources necessary for both species.

Indirect competition is expressed in the fact that one of the species worsens the conditions of existence of another species that has similar environmental requirements, without having a direct impact on the competitor.

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

For example:

* Broad-clawed and narrow-clawed crayfish cannot co-exist in the same body of water. Usually the winner is the narrow-clawed crayfish, as the most prolific and adapted to modern living conditions;

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

Classic example indirect interspecific competition are laboratory experiments conducted by the Russian scientist G.F. Gause on the joint maintenance of two types of ciliates with a similar feeding pattern.

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 release harmful substances to suppress a competitor. This was explained by the fact that these species were distinguished by unequal growth rates and the faster growing and reproducing species won in the competition for food.

Model experiments conducted by G.F. Gause led him to the formulation of the widely known principle of competitive exclusion (Gause’s theorem):

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

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

For example:

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

* Hawks and owls, which feed on approximately the same animals, avoid competition due to the fact that they hunt 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.

Predation (+ -)

Predation is a form of relationship in which individuals of one species (predators) kill and use individuals of another species (prey) as a source of food. Moreover, the predator lives separately from the prey.

This type of biotic relationships arises in the process of close contact between individuals of different species based on food connections and is widespread in nature.

From an ecological point of view, such a relationship between two species is favorable for one (predator) and unfavorable for the other (prey).

Determined that with long-term coexistence of interacting species, their changes occur in concert, i.e. the evolution of one species depends in part on the evolution of another.

Such consistency in the processes of joint development of organisms of different species is called coevolution.

A long-term connection between the populations of predator and prey in a biocenosis gives rise to their interdependence , which is especially clearly expressed in the parallel development of oppositely directed adaptations in the “predator-prey” system, i.e. natural selection will act in opposite directions.

In a predator, it will be aimed at increasing the efficiency of searching, catching and eating prey. And the prey is favored by the development of such adaptations that allow individuals to avoid detection, capture and destruction by a predator.

As the prey gains experience in avoiding the predator, the latter develops more effective mechanisms for catching it.

For example, predators have special adaptations (claws, fangs, vision, hearing, appropriate coloring, etc.) that help increase hunting efficiency. In addition, carnivores must run fast to catch prey.

Some predators use toxic substances to kill their victims (For example, Poisonous snakes) or to immobilize them (for example, a short-tailed shrew, whose saliva contains a slow-acting poison that paralyzes insects, which then remain alive for another 3-5 days, thanks to which the shrew can have a supply of “live canned food”).

However, victims have historically developed protective mechanisms in the form of the following devices:

* morphological (hard covers, thick skin, thorns, thorns, etc.);

* physiological(products of poisonous or repellent substances). This form of adaptation is quite widespread in the animal world and for some species represents the main way to reduce the pressure of predators;

* biochemical (the presence of protective coloring or the ability to change color, camouflaging in the environment);

* behavioral (hiding, running away, active defense, signaling danger, building shelters inaccessible to predators).

Thus, In all relationships between predator and prey, evolution and natural selection are constantly taking place in processes of mutual adaptation.

Wherein predator is important factor natural selection, since it prevents the accumulation of weakened or sick individuals in prey populations, which to some extent determines their progressive development.

On the other hand, prey also take an active part in this process and influence their predators, contributing to their improvement and progress.

Consequently, this struggle of mutually opposite principles is the driving force behind the evolution of both predator and prey.

Until recently, it was widely believed that all predators were harmful animals and should be destroyed. This is a misconception, since the destruction of predators often leads to undesirable consequences and causes great damage and wildlife and human economy.

For example:

* wolves contribute to intensive reproduction and increase the viability of reindeer populations in the forest-tundra and tundra;

* pike in ponds stimulate carp productivity;

* sharks, which are the main predators of the world's oceans, control the numbers of many other ocean predators. Without sharks, the oceans would become bodies of water overflowing with dead and dying fish and devoid of many healthy, commercially important fish.

As a result of the historical development of relationships in the “predator-prey” system in any biocenosis, certain population regulation mechanisms both components of the system, preventing too sharp fluctuations in numbers.

Therefore, it is always kept within a certain value approaching the optimum population density of both predator and prey.

Under natural conditions, the reproduction of the prey leads to the reproduction of the predator, which results in a decrease in the number of the prey, which in turn leads to a decrease in the number of the predator, and as a result of this, the reproduction of the prey occurs again, etc.

However, a strict dependence is almost never observed, and as the population size of one prey species decreases, predators switch to another species.

One form of predation is Cannibalism is a form of relationship in which predators feed on individuals of their own species when food resources and space are limited.

This phenomenon is observed only in extreme conditions, when other types of prey are practically inaccessible to predators.

Cannibalism is typical for many species of fish, amphibians, reptiles, and some mammals ( rats, hamsters, brown bears, martens, and also humans).

This type of relationship arose as a result of close contact between individuals of different species based on food and spatial connections and is found at all levels of the organization of living things.

This is explained by the fact that the more complex an organism is, the more favorable opportunities it provides as a habitat. On the other hand, the more perfect an organism is, the lesser the need for it to use favorable conditions in another organism becomes.

Demecology - scientific discipline, which examines the diversity of relationships between living organisms belonging to different populations. One form of such interaction is interspecific competition. In this article we will consider its features, the patterns of the emergence of struggle for territory, food and other abiotic factors in organisms living in natural and artificial biogeocinoses.

Species and its ecological characteristics

During historical development, biological taxa (groups with a certain commonality) adapt to abiotic and biotic factors of nature. The first include climate, chemical composition soil, water and air environment, etc., and to the second - the impact of the life activity of some species on others.

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

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

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

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 in biology is a type of interaction between organisms that leads to:

to a radical division of populations of different species into divergent ecological niches;
to the expulsion of one less plastic species from biogeocinosis;
to complete ellimanation of individuals from a 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 the ecosystem. The closer the ecological niches of communities of important taxa in a biotope are, the fiercer their struggle for Better conditions external environment:

territory;
food base;
residence time of the population.

Reduced pressure environment in the biotope occurs as follows:

layering in a mixed forest;
various habitats of larvae and adults. Thus, among dragonflies, naiads live on aquatic plants, and adults have mastered the air environment; In the May beetle, larvae live in the upper layers of the soil, and adult insects live in the ground-air space.

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

Results of interspecific competition

We are considering a widespread phenomenon in living nature, characterized as interspecific competition. Examples - biology and ecology (as its branch) - present us with this process both among organisms belonging to the kingdoms of fungi and plants, and in the animal kingdom.

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

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

In the process of differentiation, both competing species reduce their heritable variability and strive for 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 destructive types.

Competition occurs between organisms that have similar or identical needs and use the same resources. So one of them consumes the resources of the other, which impairs its growth, development and reproduction. This resource is usually limited. This could be food, territory, light, and the like. There are two types of competition: intraspecific, when individuals of different species or genera become competitors, and interspecific.

Intraspecific competition occurs when the needs of a certain type of organism exceed the reserves of the necessary resource and some individuals of the species do not receive enough of it. Competition increases as the population of the species increases. There are two forms: a) exploitative, when the individuals that compete do not interact directly with each other, but each receives that part of the resource that is left to it from the others; b) interference, when one individual actively prevents another from using a resource (protection of “their” territory by animals, colonization of a biotope by plants, etc.). Intraspecific competition affects fertility, mortality, growth and abundance (density). The combination of these effects of competition affects the increase in biomass, and in some cases leads to morphological changes, in particular, thinning of the stem and trunk. The struggle for light and moisture changes the habit of the crown, causes drying out and falling off of lateral branches; the formation of the apical crown can be better observed in the example of pine, spruce and other coniferous and broad-leaved species.

Interspecific competition gains acute forms between species that have similar life requirements and occupy the same ecological niche in the biogeocenosis. Thus, the vital interests of these species intersect, and they try to defeat the competitor. Competition causes oppression or complete displacement of one species from an ecological niche and its replacement by another, more adapted to environmental conditions. Competition plays an important role in the process of speciation as one of the most effective factors natural selection.

Interspecific, as well as intraspecific competition, are divided into exploitative and interference, or direct and indirect. Both forms are found in both plants and animals. An example of a direct effect on competitors is the shading of one species by another. Some plants release toxic substances into the soil, which inhibit the growth of other species. For example, chestnut leaves, when decomposed, release toxic compounds into the soil, inhibiting the growth of seedlings of other species, and several species of sage (Salvia) produce volatile compounds that negatively affect other plants. This toxic effect of some plants on others is called allelopathy. Indirect competition is not as noticeable as direct competition, and its consequences appear after prolonged exposure in the form of differential survival and reproduction.

Not all relationships between populations are ecologically equivalent: some of them are rare, others are optional, and others, such as competition, are the main mechanism for the emergence of ecological diversity.

Competition(from Latin concurrere - collide) - interaction in which two populations (or two individuals) in the struggle for the conditions necessary for life influence each other negatively, i.e. mutually oppress each other.

It should be noted that competition can also manifest itself when a resource is sufficient, but its availability is reduced due to the active opposition of individuals, which leads to a decrease in the survival rate of competing individuals.

Organisms that can potentially use the same resources are called competitors. Plants and animals compete with each other not only for food, but also for moisture, living space, shelter, nesting sites - for everything on which the well-being of the species may depend.

Intraspecific competition

If competitors belong to the same species, then the relationship between them is called intraspecific competition. Competition between individuals of the same species is the most intense and severe in nature, since they have the same needs for environmental factors. Intraspecific competition can be observed in penguin colonies, where there is a struggle for living space. Each individual maintains its own section of territory and is aggressive towards its neighbors. This leads to a clear division of territory within the population.

Intraspecific competition almost always occurs at one stage or another in the existence of a species; therefore, in the process of evolution, organisms have developed adaptations that reduce its intensity. The most important of them are the ability to disperse descendants and protect the boundaries of an individual site (territoriality), when an animal defends its nesting site or a specific area. Thus, during the breeding season of birds, the male protects a certain territory, into which, except for his female, he does not allow any individual of his species. The same picture can be observed in some fish.

Interspecific competition

If competing individuals belong to different species, then this interspecific competition. The object of competition can be any resource whose reserves in a given environment are insufficient: a limited distribution area, food, a site for a nest, nutrients for plants.

The result of competition may be the expansion of the distribution area of one species due to the reduction in numbers or extinction of another. An example is the active expansion since the end of the 19th century. range of the long-clawed crayfish, which gradually captured the entire Volga basin and reached Belarus and the Baltic states. Here it began to displace a related species, the broad-clawed crayfish.

Competition can be quite intense, for example in the fight for nesting territory. This type is called direct competition. In most cases, these conflicts occur between individuals of the same species. However, often the competitive struggle is outwardly bloodless. For example, many predatory animals that compete for food are not directly affected by other predators, but indirectly, through a decrease in the amount of food. The same thing happens in the plant world, where, during competition, some influence others indirectly, through interception nutrients, sun or moisture. This type is called indirect competition.

Competition is one of the reasons that two species, slightly different in the specifics of nutrition, behavior, lifestyle, etc., rarely coexist in the same community. Studies of the causes and consequences of interspecific competition have led to the establishment of special patterns in the functioning of individual populations. Some of these patterns have been elevated to the rank of laws.

Studying the growth and competitive relationships of two species of ciliated ciliates, Soviet biologist G.F. Gause conducted a series of experiments, the results of which were published in 1934. Two species of ciliates - Paramecium caudatum and Paramecium aurelia - grew well in monoculture. Their food was bacterial or yeast cells growing on regularly added oatmeal. When Gause placed both species in the same container, each species initially increased in number rapidly, but over time P. aurelia began to grow at the expense of P. caudatum until the second species disappeared completely from the culture. The period of disappearance lasted about 20 days.

Thus, G.F. Gause formulated law (principle) of competitive exclusion, which states: two species cannot exist in the same habitat (in the same area) if their ecological needs are identical. Therefore, any two species with identical ecological needs are usually separated in space or time: they live in different biotopes, in different forest layers, live in the same body of water at different depths, etc.

An example of competitive exclusion is the change in the numbers of roach, rudd and perch when they live together in lakes. Over time, roach displaces rudd and perch. Research has shown that competition affects the fry stage when the feeding spectra of the juveniles overlap. At this time, roach fry turn out to be more competitive.

In nature, species competing for food or space often avoid or reduce competition by moving to another habitat with acceptable conditions, or by switching to more inaccessible or difficult-to-digest food, or by changing the time (place) of foraging. Animals are divided into diurnal and nocturnal (hawks and owls, swallows and bats, grasshoppers and crickets, different kinds fish that are active at different times of the day); lions hunt larger animals, and leopards hunt smaller ones; For tropical forests The distribution of animals and birds by tiers is characteristic.

An example of the division of living space is the division of food spheres between two species of cormorant - great and long-nosed. They live in the same waters and nest on the same cliffs. Observations have shown that the long-crested cormorant catches fish swimming in the upper layers of the water, while the great cormorant forages mainly at the bottom, where it catches flounder and hip invertebrates.

Spatial separation can also be observed among plants. Growing together in one habitat, plants extend their root systems to different depths, thereby separating absorption areas nutrients and water. The depth of penetration can vary from a few millimeters in root-litter plants (such as wood sorrel) to tens of meters in large trees.