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competition in biology(from lat. concurrere- collide) - an interaction in which two populations (or two individuals) in the struggle for the conditions necessary for life affect each other negatively, i.e. mutually oppress each other. The most satisfactory formulation is that proposed by Bigon, Harper, and Townsend ( Begon, Harper, Townsend, 1986): "Competition is an interaction that boils down to the fact that one organism consumes a resource that would be available to another organism and could be consumed by it." It should be noted that competition can also appear when there is enough of some resource, but its availability is reduced due to the active opposition of individuals, which leads to a decrease in the survival of competing individuals.
Competitors called organisms that use the same resources for their life. Plants and animals compete with each other not only for food, but also for light, moisture, food, living space, shelters, nesting places - for everything on which the well-being of the species may depend.
There are two types of competition: intraspecific competition and interspecific. Intraspecific competition is competition between members of one or more populations of a species for a resource when it is in short supply. Competition is extremely widespread in nature. Competition between individuals of the same species living in the same territory is the most acute and tough in nature, since they have the same needs for environmental factors.
intraspecific competition at one or another stage of the existence of a particular species, it almost always occurs, therefore, in the process of evolution, organisms have developed adaptations that reduce its intensity. The most important of them are the ability to resettle descendants and the protection of the boundaries of an individual site (territoriality), when an animal protects its nesting place or a certain area, a sexual partner, a place for reproduction, and the ability to get food. Thus, intraspecific competition is a struggle between individuals of the same species. Intraspecific struggle for existence increases with an increase in the size of the population, a reduction in the area (territory) and an increase in the specialization of the species.
Examples of intraspecific territorial competition in animals
Rivalry individuals of one species for a food resource, when it is not enough, can be observed in a population of field mice of one species. Looking for and consuming food, mice expend energy and put themselves at risk of being eaten by predators. Under favorable conditions, when there is enough food, the population density increases and at the same time there is a need for organisms to spend more energy searching for food. As a result, the chances of survival are reduced.
intraspecific competition can be expressed in direct aggression (active competition), which can be physical, psychological or chemical. For example, males competing for the right to possess a female may fight among themselves. Demonstrate your appearance to outshine the opponent, or use the smell to keep rivals at a distance. The struggle for females, space and light often leads to intense competition.
Territoriality- territoriality. Active dispersal of individuals of one or different types in space, due to competition for the space itself and the resources available in it. ( Source: English-Russian dictionary genetic terms").
Some fish, many species of birds and other animals are characterized by the so-called territoriality - intraspecific competition for space. In birds, this competition is manifested in the behavior of males. For example, at the beginning of the breeding season, the male chooses a habitat area (territory) and defends it from the invasion of males of the same species (birdsong in the spring is a signal of ownership of the occupied area). This is how males of many species of birds determine the competitiveness of opponents by voice, and they take seriously only equal in age or older birds, American ornithologists have proven. In a protected area, care for the nest and juveniles will not be disturbed by the presence of other parental pairs. During the breeding season of birds, the male guards a certain territory, to which, except for his female, he does not allow a single individual of his species. And the louder the male screams, the more he will frighten the invader, the bird intensifies its singing, and soon goes on the offensive. A couple that has secured a territory is more likely to find enough food for itself, and this helps to do everything necessary to breed offspring.
Territorial behavior is understood as a set of signaling means that ensure dispersal and regulate the relations of owners of neighboring or partially overlapping habitats. In different species of animals, these signals can be contact and distant (singing birds, howling wolves, chirping grasshoppers, etc.). A set of visual and tactile threatening signals (up to open aggression and a fight) is used when neighbors collide on a common border and territory. Many vertebrates use sounds to determine their territory. Male howler monkeys defend their vast territory by uttering an extremely loud roar that can be heard 5 km away. Each type of howler is characterized by its own special sound. A variety of odorous substances are used to mark boundaries in some animals.
Animals protect their territory with the help of special signs and by this they try to expel strangers from it. Animals mark their territory using sounds, light signals, smells, and also scare uninvited guests with claws, pincers or plumage. Animals such as sea lions and elephant seals only defend their territory during the mating season, and the rest of the time they do not show signs of aggression towards other members of their species. Frogs and fish also compete for territory only during the mating season. Everyone heard the evening triads of frogs in a pond not far from home. The male stickleback during the breeding season defends the area around the nest from invasion by other males.
Interesting chemical signals with which animals mark their territory can be observed in roe deer and antelope. In the autumn, the Siberian roe deer peels off the bark of small trees and shrubs with its horns, and then rubs its head or neck against them. So she leaves chemical marks on the bare parts of trees, which are secreted by special glands located on the head and neck. Trees marked in this way indicate to other individuals of the population of this species of roe deer that the territory is occupied or that another animal passed through here. It is possible that other animals determine the time of passage (marking) of the host animal by the intensity of chemical secretions on the mark. Sometimes these same roe deer knock out patches of earth with their hooves, leaving a long-lasting smell between their finger glands.
Antelopes, on bushes and tall grasses, bite off the top of the shoot and, touching the cut in front of the orbital gland, leave a mark. A large gerbil, as a rule, makes signal mounds, raking the ground under itself, and irons them from above with its belly, where it has a mid-abdominal gland that secretes pheromones (special chemicals). The badger marks the entrance to the hole with a secret under the tail gland, the rabbit marks the chin gland. Many species of lemurs leave scented secrets on the branches they move on.
Some rodents use interesting markings as a boundary to their territory. A large gerbil, as a rule, makes signal mounds, raking the ground under itself, and irons them from above with its belly, where it has a mid-abdominal gland that secretes pheromones (special chemicals). Two species of singing mice live in the forests of Panama and Costa Rica, Scotinomys teguina and S. xerampelinus who, like birds, mark their allotments with their voice. Both types of mice make special vocal sounds, which a person, however, can hardly make out. This is not just a squeak: rodents stand on their hind legs, throw their heads back and produce a series of repeating sounds, similar to a trill.
The movement of house mice occurs along the same routes, thanks to the persistent smells of pheromones that are released along with the urine. On the paws of each individual there are also special glands with which they "mark" the territory. The scent of these glands is transmitted to any object they touch. Urine also serves as a kind of signaling device.
Scientists have established the presence in the urine of rats not only of metabolic products, but also of a number of other components - pheromones, which in rats serve as signals that determine the position and state of the individual.
The muskrat is a sedentary and territorial animal that actively guards its territory from invading neighbors. The borders are marked with heaps of excrement on elevated places near the water. Also, the animals mark the boundaries of their “possession” with secretions of the glands, the strong smell of which serves as a signal that this area is busy.
Canids and cats urinate in certain places, thus declaring a certain territory. Dogs mark their territory with both urine and feces, thus spreading information about themselves that other members of their species can get. Cats also mark their territory with urine. Cats additionally mark their territory with secrets (fluid) that is secreted between the fingers and from the glands located in the area from the corner of the lips to the base of the ear. Marks left by a dog in the form of excrement, the smell of which can be enhanced by the secretion secreted from special glands located in the anus of the animal, do not last long. This secret gives the dog feces a unique smell. However, this substance carries short-term information, since it has the ability to quickly volatilize. In addition, dogs themselves actively lick anus thus getting rid of this smell. With the help of claws and urine, the tiger marks its territory on the bark of trees. Claw prints on the bark carry information about the size and social status of the predator that left them.
Bears mark their territory by rubbing their backs against trees, “hanging” tufts of wool on the trunks. First, they make special track marks: when they approach the border tree, they radically change their gait and leave deeper, more noticeable tracks. Then they tear off pieces of bark from the tree, scratch it and make snacks. At the same time, they can bite a tree at different heights: standing on four and on two legs. In addition, the bear marks its territory with scent marks, leaving secretions of glands on trees in the notches from the claws. To divide the space, bears often use a loud signal call. Sometimes individuals simply attack each other.
Stages of development of territoriality:
The first stage in the development of territoriality is the individual space surrounding each individual. It is clearly visible, for example, in rooks perched on a tree, or in starlings in a flying flock. An individual protects it from intrusion and opens it to another individual only after courtship ceremonies before mating.
The second stage is a defended place for living, resting or sleeping in the middle of a non-defended activity zone (for many predators of a hunting area). Animals standing on the second step are distributed almost evenly. These are bears, tigers, hyenas, and also rodents.
The third step is the rational use of space, where real territories are formed - areas from which other individuals are expelled. The owner of the site dominates it, he is often psychologically stronger than the stranger who tried to penetrate his territory, and often for the expulsion in most cases it is enough only demonstrations, threats, persecution, at most - feigned attacks that stop at the boundaries of the site, marked visually, acoustically or smell (olfactory). It was noticed that even smaller individuals expelled larger relatives from their area. So it was repeatedly observed that a much smaller and younger muskrat drove a larger and older muskrat from its site. Using the examples of other animals, scientists have found that almost always the owner of the site drove away an outside representative of his own species who encroached on his territory.
Conclusion:
Territorial competition in animals manifests itself in the absence of a shortage of resources and contributes to the optimization of the existence of each individual of a given species. Each individual holds its own piece of territory and is aggressive towards its neighbors. This leads to a clear division of the territory within the population.
Territorial behavior is found in a wide range of animals, including fish, reptiles, birds, mammals and social insects. This phenomenon is based on the innate desire of an individual for freedom of movement on a certain minimum area.
* Symbiosis and Mutualism
* Predation
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 has completely supplanted 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 inhibit 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. Fast growth and early establishment of leafiness give advantages in the initial 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 feeding grounds, 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 the natural community. Generating and consolidating the diversity of organisms, it helps to increase the resilience of communities, more efficient use of available resources ...
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 end, communities 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.
Investigating 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 two representatives of the same genus meet from a height of 1000 to a height of 3400 m, then each has an interval of 1200 m, and if three species of the same genus live in the same altitude range, 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 was competition rather than abiotic factors that limited 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 the most diverse 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 press of predators played in this case The decisive role is played by the disappearance of the polar hare from those areas where the white hare has not penetrated, 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, above we have already mentioned the “plankton paradox”, 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 changes 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.
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 the available resource. 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 environment, 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. Obviously, 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 graph axes (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 zero growth isoclines 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 obtained data, 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 species of planktonic algae living within a small volume of water (remember the "plankton paradox"), or the number of species of herbaceous plants 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 concept when discussing the models shown 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 each point on a given isocline, the birth rate, by definition, is equal to the death rate, but this does not mean that the ratio in the 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 FROM, 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 equilibrium point of resources 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 species A consumes the second resource more, and species 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 limited 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 the area of 4 both species successfully coexist; in the area of 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 each pair of species can coexist (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 to nature from an idealized model, 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 plot measuring 12 × 12 m 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 provide a real possibility of coexistence immediately. a large number species (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. Due 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 in 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 somewhat 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 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 under 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 1920s. C. Elton (1934; Elton, 1927).
A similar situation was observed, however, in physics. As Weisskopf (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 putting general issues and receive specific answers, scientists began to ask more specific questions, but, surprisingly, they received 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 "... the minimum 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 a particular 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).
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 removal sea urchins showed 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 narrow-clawed crayfish is the winner, as the most prolific and adapted to modern conditions 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.
The interactions of species in the composition of the biocenosis are characterized not only by links along the line of direct trophic relationships, but also by numerous indirect links that unite species of both the same and different trophic levels.
Competition- this is form of relationship that occurs when two species use the same resources(space, food, shelter, etc.).
Distinguish 2 forms of competition:
- direct competition, in which directed antagonistic relations develop between species populations in the biocenosis, expressed in various forms of oppression: fights, chemical suppression of a competitor, etc.;
- indirect competition, expressed in the fact that one of the species worsens the habitat conditions for the existence of another species.
Competition can be both within a species and between several species of the same genus (or several genera):
Intraspecific competition occurs between individuals of the same species. This type of competition is fundamentally different from interspecific competition and is expressed mainly in the territorial behavior of animals that protect their nesting sites and a certain area in the area. These are many birds and fish. The relationships of individuals in populations (within a species) are diverse and contradictory. And if specific adaptations are useful for the entire population, then for individual individuals they can be harmful and cause their death. With an excessive increase in the number of individuals, intraspecific struggle intensifies. That is, intraspecific struggle is accompanied by a decrease in fertility and the death of some individuals of the species. There are a number of adaptations that help individuals of the same population avoid direct confrontation with each other - you can meet mutual assistance and cooperation (joint feeding, raising and protecting offspring);
Interspecific competition is any interaction between populations that adversely affects their growth and survival. Interspecific struggle is observed between populations of different species. It proceeds very quickly if the species need similar conditions and belong to the same genus. The interspecific struggle for existence includes the unilateral use of one species by another, i.e., the "predator-prey" relationship. A form of the struggle for existence in the broad sense is the favoring of one species to another without harming itself (for example, birds and mammals distribute fruits and seeds); mutual favoring of one species to another without prejudice to itself (for example, flowers and their pollinators). Fight against adverse conditions environment observed in any part of the range when external environmental conditions worsen: with daily and seasonal fluctuations in temperature and humidity. Biotic interactions between populations of two species are classified into:
neutralism - when one population does not affect another;
competition - the suppression of both species;
amensalism - one population suppresses another, but does not itself experience a negative impact;
predation - predator individuals are larger than prey individuals;
commensalism - a population benefits from association with another population, and the latter is indifferent;
proto-cooperation - interaction is favorable for both species, but not necessarily;
mutualism - the interaction must necessarily be favorable for both species.
An example of a model of interpopulation interactions is “the spread of individuals of the “sea acorn” - balyanus, which settle on rocks above the intertidal zone, because they cannot withstand drying. Smaller Chthameclus, on the other hand, occur only above this zone. Although their larvae settle in the settlement zone, direct competition from the balanuses, which are able to disrupt competitors from the substrate, prevents their appearance in this territory. In turn, balyanuses can be replaced by mussels. But still, later, when mussels occupy the entire space, balanuses begin to settle on their shells, again increasing their numbers. In competition for nesting shelters, the great tit dominates the smaller tit, capturing nest boxes with an entrance bigger size. Out of competition, blue tit prefer a 32 mm entrance, and in the presence of a great tit they settle in hollows with a 26 mm entrance, unsuitable for a competitor. In forest biocenoses, competition between wood mice and bank voles leads to regular changes in the biotopic distribution of species. In years with increased numbers, wood mice populate various biotopes, displacing bank voles to less favorable places.
The main types of interpopulation relationships ("predator - prey", mutualism, symbiosis)
Competitive relationships can be very different - from direct physical struggle to peaceful coexistence. And at the same time, if two species with the same ecological needs find themselves in the same community, then one competitor will definitely crowd out the other. This environmental rule is called "law competitive exclusion", formulated G.F. Gause. According to the results of his experiments, it can be said that among species with a similar nature of nutrition, after some time, individuals of only one species remain alive, surviving in the struggle for food, since its population grew and multiplied faster. He is the winner in the competition. a species that, in a given ecological situation, has at least small advantages over others, and, consequently, greater adaptability to environmental conditions.
Competition is one of the reasons why two species that differ slightly in the specifics of nutrition, behavior, lifestyle, etc., rarely cohabit in the same community. In this case, the competition is direct hostility. The fiercest competition, with unforeseen consequences, occurs when man introduces animal species into communities without regard for already established relationships. But often competition manifests itself indirectly, is of an insignificant nature, because. different kinds perceive the same environmental factors differently. The more diverse the possibilities of organisms, the less intense the competition will be.
Mutualism(symbiosis) - one of the stages in the development of the dependence of two populations on each other, when association occurs between very different organisms and the most important mutualistic systems arise between autotrophs and heterotrophs. Classical examples of mutualistic relationships are anemones and fish living in the corolla of their tentacles; hermit crabs and sea anemones. Other examples of this type of relationship are known. Thus, the worm Aspidosiphon at a young age hides its body in a small empty gastropod shell.
Mutualistic forms of relationships are also known in the plant world: in the root system of higher plants, connections are established with mycorrhiza-forming fungi and nitrogen-fixing bacteria. Symbiosis with mycorrhizal fungi provides plants with minerals, and fungi with sugars. Similarly, nitrogen-fixing bacteria, supplying the plant with nitrogen, receive carbohydrates (in the form of sugars) from it. On the basis of such relations, a complex of adaptations is formed that ensures the stability and functional efficiency of mutualistic interactions.
Closer and biologically significant forms of connections arise in the so-called endosymbiosis -cohabitation, in which one of the species settles inside the body of another. Such are the relations of the higher animals with the bacteria and protozoa of the intestinal tract.
Many animals contain photosynthetic organisms (mainly lower algae) in their tissues. The settlement of green algae in the wool of sloths is known, while the algae use the wool as a substrate, and for the sloth they create a protective color.
The symbiosis of many deep-sea fish with luminous bacteria is peculiar. This form of mutualism provides the light coloration that is so important in the dark by creating luminous organs - photophores. The tissues of the luminous organs are abundantly supplied with nutrients necessary for the life of bacteria.
Predation. Laws of the "predator-prey" system
Predator -it is a free-living organism that feeds on other animal organisms or plant foods, i.e., the organisms of one population serve as food for the organisms of another population. The predator, as a rule, first catches the prey, kills it, and then eats it. To do this, he has special devices.
At victims also historically developed protective properties in the form of anatomical, morphological, physiological, biochemical features, for example: body outgrowths, spikes, spines, shells, protective coloration, poisonous glands, the ability to burrow into the ground, quickly hide, build shelters inaccessible to predators, resort to signaling danger.
As a result of such interdependent adaptations, certain groupings of organisms as specialized predators and specialized prey. An extensive literature is devoted to the analysis and mathematical interpretation of these relationships, starting with the classical Volterra-Lotka model (A Lotka, 1925; V. Volterra, 1926, 1931) and up to its numerous modifications.
The laws of the "predator - prey" system (V. Volterra):
- law periodic cycle - the process of prey destruction by a predator often leads to periodic fluctuations in the population size of both species, depending only on the growth rate of the predator and prey populations, and on the initial ratio of their numbers;
- law preservation of averages - the average population size for each species is constant, regardless of the starting level, provided that the specific rates of population increase, as well as the efficiency of predation, are constant;
- law violations of averages - with a similar violation of the predator and prey population (for example, fish during fishing in proportion to their abundance), the average number of the prey population increases, and the predator population decreases.
Volterra-Lotka model. The "predator-prey" model is considered as a spatial structure. Structures can form both in time and space. Such structures are called "spatio-temporal".
An example of temporal structures is the evolution of the number of mountain hares and lynxes, which is characterized by fluctuations in time. Lynxes feed on hares, and hares eat vegetable food, which is available in unlimited quantities, so the number of hares increases (increase in the supply of available food for lynxes). As a result, the number of predators increases until a significant number of them becomes, and then the destruction of hares occurs very quickly. As a result, the number of prey decreases, the food reserves of lynxes run out and, accordingly, their numbers decrease. Then again the number of hares increases, respectively, the lynxes begin to multiply rapidly, and everything repeats from the beginning.
This example is considered in the literature as the Lotka-Volterra model, which describes not only population fluctuations in ecology, it is also a model of undamped concentric fluctuations in chemical systems.
Limiting factors
The concept of limiting factors is based on two laws of ecology: the law of the minimum and the law of tolerance.
The law of the minimum. In the middle of the century before last, a German chemist Y. Liebig(1840), studying the effect of nutrients on plant growth, found that the yield does not depend on those nutrients that are required in large quantities and are present in abundance (for example, CO 2 and H 2 0), but on those that, although and are needed by the plant in smaller quantities, but are practically absent in the soil or inaccessible (for example, phosphorus, zinc, boron). Liebig formulated this pattern as follows: "The growth of a plant depends on the nutrient element that is present in minimum quantity This conclusion later became known as Liebig's law of the minimum and was extended to many other environmental factors.
Heat, light, water, oxygen, and other factors can limit or limit the development of organisms if their value corresponds to the ecological minimum.
For example, tropical fish "angelfish" die if the water temperature drops below 16°C. And the development of algae in deep-sea ecosystems is limited by the depth of penetration of sunlight: there are no algae in the bottom layers.
Liebig's law of the minimum can be formulated as follows:growth and development of organisms depend, first of all, on those factors of the natural environment, the values of which are approaching the ecological minimum.
Research has shown that the law of the minimum has 2 limitations that should be considered in practice:
- The first limitation is that Liebig's law is strictly applicable only in conditions stationary system state.
For example, in a certain body of water, algae growth is naturally limited by a lack of phosphate. At the same time, nitrogen compounds are contained in water in excess. If in such a reservoir they begin to dump wastewater with a high content: mineral phosphorus, then the reservoir can "bloom". This process will progress until one of the elements is used up to the limiting minimum. Now it could be nitrogen if the phosphorus continues to flow. At the transitional moment (when nitrogen is still insufficient, but phosphorus is already sufficient), the effect of the minimum is not observed, i.e., none of these elements affects the growth of algae;
- second constraint associated with interaction of several factors. Sometimes the body is able replace the deficient element others, chemically related .
So, in places where there is a lot of strontium, in mollusk shells, it can replace calcium with a lack of the latter. Or, for example, the need for zinc in some plants is reduced if they grow in the shade. Therefore, a low concentration of zinc will limit plant growth less in the shade than I in bright light. In these cases, the limiting effect of even an insufficient amount of one or another element may not manifest itself.
Law of Tolerance(from lat. tolerance- patience) was discovered by an English biologist W. Shelford(1913), who drew attention to the fact that not only those environmental factors, the values of which are minimal, but also those that are characterized by ecological maximum. Excess heat, light, water, and even nutrients can be just as devastating as their deficiency. W. Shelford called the range of the ecological factor between the minimum and maximum the "tolerance limit".
Limit of tolerancedescribes the amplitude of fluctuations of factors, which ensures the most complete existence of the population.
Later, tolerance limits were established for various environmental factors for many plants and animals. The laws of J. Liebig and W. Shelford helped to understand many phenomena and the distribution of organisms in nature. Organisms cannot be distributed everywhere because populations have a certain tolerance limit in relation to fluctuations in environmental environmental factors.
W. Shelford's Law of Tolerance is formulated like this: growth and development of organisms depend, first of all, on those environmental factors, the values of which approach the ecological minimum or ecological maximum. The following has been established:
Organisms with a wide range of tolerance to all factors are widely distributed in nature and are often cosmopolitan (for example, many pathogenic bacteria);
Organisms can have a wide range of tolerance for one factor and a narrow range for another (for example, humans are more tolerant of the absence of food than the absence of water, i.e. the tolerance limit for water is narrower than for food);
If the conditions for one of the environmental factors become suboptimal, then the tolerance limit for other factors may also change (for example, with a lack of nitrogen in the soil, cereals require much more water);
The real limits of tolerance observed in nature are less than the body's potential to adapt to this factor. This is explained by the fact that in nature the limits of tolerance in relation to the physical conditions of the environment can be narrowed by biological relations: competition, lack of pollinators, predators, etc. Any person better realizes his potential
opportunities in favorable conditions (for example, gatherings of athletes for special training before important competitions). The potential ecological plasticity of an organism, determined in laboratory conditions, is greater than the realized possibilities in natural conditions. Accordingly, distinguish potential and implemented ecological niches;
- limits of tolerance in breeding individuals and there are fewer offspring than in adults, that is, females during the breeding season and their offspring are less hardy than adult organisms.
Thus, the geographical distribution of game birds is more often determined by the influence of climate on eggs and chicks, and not on adult birds. Care for offspring and respect for motherhood are dictated by the laws of nature. Unfortunately, sometimes social "achievements" contradict these laws;
Extreme (stress) values of one of the factors lead to a decrease in the tolerance limit for other factors.
If heated water is dumped into the river, then fish and other organisms spend almost all their energy coping with stress. They do not have enough energy to obtain food, protection from predators, reproduction, which leads to gradual extinction. Psychological stress can also cause many somatic (from the Greek. soma- body) diseases not only in humans, but also in some animals (for example, in dogs). With stress values of the factor, adaptation to it becomes more and more difficult.
Many organisms are able to change tolerance to individual factors if conditions change gradually. You can, for example, get used to the high temperature of the water in the bath, if you climb into hot water, and then gradually add hot water. This adaptation to the slow change of the factor is a useful protective property. But it can also be dangerous. Unexpected, without warning signals, even a small change can be critical. Coming threshold effect. For example, a thin twig can break a camel's already overstretched back.
If the value of at least one of the environmental factors approaches a minimum or maximum, the existence and development of an organism, population or community becomes dependent on this factor, which limits life activity.
The limiting factor isany environmental factor approaching or exceeding the extreme values of the tolerance limits. Such strongly deviating factors become of paramount importance in the life of organisms and biological systems. It is they who control the conditions of existence.
The value of the concept of limiting factors lies in the fact that it allows you to understand the complex relationships in ecosystems. Note that not all possible environmental factors regulate the relationship between the environment, organisms and humans. Priority in one or another period of time are various limiting factors. It is on them that attention should be focused in the study of ecosystems and their management. For example, the oxygen content in terrestrial habitats is high, and it is so available that it almost never serves as a limiting factor (with the exception of high altitudes, anthropogenic systems). Oxygen is of little interest to terrestrial ecologists. And in water, it is often a factor limiting the development of living organisms ("kills" of fish, for example). That's why hydrobiologist measures the oxygen content in water, unlike a veterinarian or an ornithologist, although oxygen is no less important for terrestrial organisms than for aquatic ones.
Limiting factors determine and geographic range kind. Thus, the movement of organisms to the north is limited, as a rule, by a lack of heat.
The spread of certain organisms is often limited and biotic factors.
For example, figs brought from the Mediterranean to California did not bear fruit there until they guessed to bring there a certain type of wasp - the only pollinator of this plant.
The identification of limiting factors is very important for many activities, especially agriculture. With a targeted impact on the limiting conditions, it is possible to quickly and effectively increase the yield of plants and the productivity of animals.
So, when wheat is grown on acidic soils, no agronomic measures will have an effect if liming is not used, which will reduce the limiting effect of acids. Or if you grow corn on soils with a very low phosphorus content, then even with enough water, nitrogen, potassium and other nutrients, it stops growing. Phosphorus is the limiting factor in this case. And only phosphate fertilizers can save the crop. Plants can also die from too much water or excess: fertilizers, which in this case are limiting factors.
Knowing the limiting factors provides the key to ecosystem management. However, at different periods of the life of the organism and in different situations various factors act as limiting factors. Therefore, only skillful regulation of the conditions of existence can give effective management results.
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