DEGREES OF COMPARISON OF ADJECTIVES In English, as in Russian, ...
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 manifest itself 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, shelter, nesting - 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 your 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 the same or different species 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 those of equal 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 protects a certain territory, to which, except for his female, he does not allow any 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 contributes to doing 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 animal species, 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 emitting 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 rational use spaces where real territories are formed - sites 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. On 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.
Intraspecific competition has its own characteristics. The reason for its occurrence is a typical situation when the resource for which the individuals of the population are fighting is quantitatively limited. There is fierce competition (for territory, food resources, etc.), which is observed at a high population density.
Another form of intraspecific competition is rivalry, when one individual does not allow another to occupy an existing territory and use its resources. In this case, a form of ideal or uncompromising competition is possible, which is decided by emigration to other territories.
The severity of competition and its impact on the population depends on the density, which determines the frequency and intensity of contacts between competitors.
Intraspecific competition not only impoverishes resources and thereby leads to increased mortality, stunted growth of individuals, it encourages self-aggression, cannibalism, and reduces the potential contribution of an individual to the next generation and population development.
Intraspecific competition between individuals of a population in plants can be characterized as a struggle for light, heat, moisture, and the area of mineral nutrition. In this competition, organisms that are nearby are more developed, displacing the weak completely or strongly suppressing their development and leading to gradual death. That is why, in agrophytocenoses, in order to reduce competition and create optimal conditions for the growth and development of cultivated plants, the density of individuals and the area of their mineral nutrition are regulated by the appropriate type of sowing or thinning of crops, the destruction of weeds and the selection of biologically compatible species for mixed crops.
In natural plant populations, self-recovery takes place - a decrease in the number of individuals per unit area.
This phenomenon is known to foresters. The number of trees per unit area decreases with the age of the stands. The liquefaction of the forest stand occurs the faster, the more photophilous the species and the better environmental conditions. The latter is associated with an increase in the growth rate in good conditions and, accordingly, an increase in its needs, from which competition becomes intense (Fig. 9.2).
Each species has its own optimal density, i.e. such a degree of saturation of the territory of the population with its individuals, which ensures the best reproduction and the greatest stability of the population, reduces the severity of competition.
In animals of different species, too, in the process of evolution, appropriate adaptive adaptations have been developed for life in an environment that is sparsely saturated or densely populated with individuals.
Appropriate biological properties and a life strategy have been developed that enable organisms to reproduce and survive in a “competitive vacuum” (lack or little competition). In the first case, small animals can breed, their descendants will survive, although the population density will be high.
In the second case, large animals and relatively similar descendants can compete for space and food. Therefore, the main energy of organisms is directed to competition, to increase their survival, to produce competitive offspring.
These trends and strategy various kinds reflected in two opposite types of natural selection: r - and k - selection, which are discussed in chapter 2.
Intraspecific competition between plant individuals of the same population can be calculated using the Yoda equation. According to this equation, the average area per individual (a) is inversely proportional to the population density (d).
Competition(from late Latin concurentia - collide), a type of relationship between organisms of the same or different species competing for the same environment resources(sexual partners, food, territory, shelters, etc.) with a lack of the latter. Intraspecific competition is considered as the most important form of the struggle for existence, since potentially the most acute competitive relations arise between more similar individuals. For example, in mammals, competition between males for possession of a female during the breeding season is expressed in a vivid form. During the rut, males of many species ( deer, rams, bears) arrange fierce tournament fights.
Competition for territory, shelters and food is most fully expressed in territorial species with a solitary lifestyle (some mouse-like rodents, mole rats, predatory mammals). However, in nature there are mechanisms (environmental, behavioral, etc.) that reduce the intensity of intraspecific competition. For example, many aggressive actions of animals during mutual contacts are ritualized and are intended, first of all, to intimidate the enemy, not bringing the contact to physical interaction.
Interspecific competition is more often observed between individuals of ecologically close species that use the same habitats and food resources. Such functionally similar groups of species that interact strongly with each other and weakly with other types of biocenosis are often distinguished in guilds (the term was proposed by R. B. Root in 1967). The concept of guilds is closely related to the ecological niche model.
Competition can be passive (indirect), through the consumption of environmental resources necessary for both species, and active (direct), accompanied by the suppression of one species by another. The first option is often called operational competition, and the second - interference. An example of active competition is the relationship between acclimatized American and native European minks, in which the native view turned out to be uncompetitive.
The state of competition in the long term is not energetically beneficial for both competitors, therefore, various mechanisms are implemented in nature that reduce the intensity of interspecific competitive relations, based, in particular, on the division of resources and the formation of differing ecological niches. The result of the action of intraspecific and interspecific competition, as a rule, is different (see also Speciation). The first leads to the culling of the least competitive (least adapted) individuals and, under conditions of an unchanged environment, to a narrowing of the rate of reaction of the species, specialization (stabilizing selection; see below). Natural selection), and under conditions of a directionally changing environment - to a shift in the reaction rate in the direction determined by the changing environment, i.e., to the emergence of a new adaptive form (driving selection; see Natural selection).
intraspecific competition
Interspecific competition leads to further divergence of species due to the culling of morphs with similar requirements.
Natural selection), and under conditions of a directionally changing environment - to a shift in the reaction rate in the direction determined by the changing environment, i.e., to the emergence of a new adaptive form (driving selection; see Natural selection). Interspecific competition leads to further divergence of species due to the culling of morphs with similar requirements.
In natural communities, animals of the same and different species live together and interact with each other. In the process of evolution, certain relationships are developed between animals, reflecting the connections between them. Each species of animal performs a specific role in the community in relation to other living organisms.
The most obvious form of relationship between animals is predation. In natural communities, there are herbivores that feed on vegetation, and there are carnivores that catch and eat other animals. In relationships, herbivores act victimsami, and carnivores - predatorami. At the same time, each prey has its own predators, and each predator has its own "set" of victims.
INTRA-SPECIES COMPETITION
So, for example, lions hunt zebras, antelopes, but not elephants and mice. Insectivorous birds catch only certain types of insects.
Predators and prey have evolved to adapt to each other so that some have developed body structures that allow them to catch as best as possible, while others have such a structure that allows them to better run or hide. As a result, predators catch and eat only the weakest, sickest and least adapted animals.
Carnivores do not always eat herbivores. There are predators of the second and third order, which eat other predators. This is often found among aquatic inhabitants. So some species of fish feed on plankton, the second - on these fish, and a number of aquatic mammals and birds eat the latter.
Competition- a common form of relationships in natural communities. Usually, competition is most acute between animals of the same species living in the same territory. They have the same food, the same habitats. Between animals of different species, the competition is not so sharp, since their lifestyles and needs are somewhat different. So the hare and the mouse are herbivores, but they eat different parts of plants and lead a different lifestyle.
Population Relationships of individuals in a population
A population is a collection of individuals of the same species that have a common living space and type of relationship with each other. Individuals of the population differ among themselves in age and vitality (i.e.
Competition (biology)
life force), which can be determined genetically, phenetically, and more often - a combination of these factors.
A number of significant differences that need to be taken into account in population studies are populations of plants and animals. The main difference lies in the fact that animals with mobility can react more actively to the prevailing environmental conditions, avoiding unfavorable circumstances or dispersing over the territory to compensate for the decrease in the resource reserve per unit area. Mobility makes it easier for them to protect themselves from predators.
Due to the fact that populations are diverse, the interactions of the individuals that make up them also differ.
The main type of interaction between individuals in a population is competition, i.e. competition for the consumption of a resource that is in short supply. Competition can be symmetrical (competing individuals have the same effect on each other) or asymmetric (influence of individuals on each other varies in strength).
features of the competition of individuals in the population:
1. Competition reduces the growth rate of individuals, can slow down their development, reduce fertility and, as a result, reduce the contribution to the next generations. The number of descendants of a particular individual is the smaller, the tougher the conditions of competition and the less resources it got.
2. In most cases, individuals compete for resources: each individual receives that limited amount of resources that was not consumed by its competitors. Such competition is called exploitative. Less often there is a competition for physical space, when individuals “mechanically” prevent each other from obtaining a resource, for example, the protection of their territory by mobile animals. Such relationships are called interference.
3. Different individuals have different competitive ability. Despite the fact that all individuals of a population are potentially equivalent (their gene pool is constantly leveled due to hybridization), there is no equivalence of individuals in nature. As a result of asymmetric competition, a decrease in population density occurs: weak plants die, and weak animals migrate to habitats with a lower the level of competition.
In addition to competition, other forms of relations between individuals in populations are also possible - neutrality (if there are so many resources and so few individuals that they practically do not interfere with each other) and positive relationships.
Mutually beneficial (or beneficial for some individuals) relationships between animals are well known: parental care for offspring, the formation of large family groups, a herd lifestyle, collective defense from enemies, etc. "Caravans" of birds lining up in lines, wedges, ledges, etc. ., allow the wings of individual individuals, due to aerodynamic effects, to acquire greater lift (it is easier to fly in a team). There is an opinion that fish swimming in a flock also receive hydrodynamic advantages.
Much less known is the role of mutual aid in plants. Plants sown in a group develop better, since in this case they more easily form symbiosis with fungi and bacteria of the mycorrhiza and rhizosphere (the so-called “group effect”).
Phenomena of mutual assistance of plants are possible during the "collective defense" from phytophages, which exhibit excessively high activity and can seriously damage plants. In this case, after the start of active eating by phytophages, biochemical reactions occur in plants and the concentration of substances that reduce their palatability (cyanides, etc.) increases. Cases are described when individuals attacked by phytophages released signal substances into the atmosphere (“they eat me” signal), which caused an increase in the formation of cyanides in those individuals that were not yet damaged.
⇐ Previous45678910111213Next ⇒
Related information:
Site search:
Competition is the competition of organisms of the same trophic level (between plants, between phytophages, between predators, etc.) for the consumption of a resource that is available in limited quantities.
a special role is played by competition for the consumption of resources 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 both cases when intraspecific competition is more acute than interspecific, and vice versa. At the same time, the intensity of competition within a population and between populations can vary in various conditions. If conditions are unfavorable for one of the species, then competition between its individuals may increase. In this case, it can be displaced (or, more often, displaced) by a species for which these conditions are more suitable.
However, in multi-species communities, pairs of "duelists" most often do not form, and competition is diffuse in nature: many species simultaneously compete for one or more environmental factors. "Duelists" can only be mass plant species that share the same resource (for example, trees - linden and oak, pine and spruce, etc.).
Plants can compete for light, for soil resources, and for pollinators. On soils rich in mineral nutrition resources and moisture, dense dense plant communities are formed, where the limiting factor for which plants compete is light.
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. At the same time, large ungulates can compete with insects like locusts or mouse-like rodents that can destroy most of the grass in years of mass reproduction. 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 relations between individuals of the same population, competition between species (their populations) can be symmetrical or asymmetric. At the same time, the situation when environmental conditions are equally favorable for competing species is quite rare, and therefore relations of asymmetric competition arise more often than symmetrical ones.
With fluctuating resources, which is usually in nature (moisture or mineral nutrients for plants, primary biological products for different species of phytophages, the density of prey populations for predators), different competing species alternately receive advantages. This also leads not 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 survive the deterioration of environmental conditions with a decrease in the level of metabolism or even transition to a state of rest.
The outcome of competition is also influenced by the fact that a population with more individuals and which, accordingly, will more actively reproduce “its own army” (the so-called mass effect) is more likely to win the competition.
23. The relationship of the plant phytophage and prey predator
RELATIONSHIP "PLANT-PHYTOPHAGE".
The relationship "phytophage - plant" is the first link in the food chain, in which the substance and energy accumulated by producers are transferred to consumers.
It is equally “unprofitable” for plants to be eaten to the end or not eaten at all. For this reason, in natural ecosystems, there is a tendency to form an ecological balance between plants and phytophages that eat them. For this plant:
- are protected from phytophages by thorns, form rosette forms with leaves pressed to the ground, inaccessible to grazing animals;
- protect themselves from complete grazing biochemically, producing toxic substances with increased consumption, which make them less attractive to phytophages (this is especially true for slow-growing patients). In many species, when they are eaten, the formation of "tasteless" substances is enhanced;
- emit odors that repel phytophages.
Protection from phytophages requires a significant expenditure of energy, and therefore trade off can be traced in the relationship “phytophage – plant”: the faster the plant grows (and, accordingly, the better conditions for its growth), the better it is eaten, and vice versa, the slower the plant grows, the less attractive it is for phytophages.
At the same time, these means of protection do not ensure the 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 start 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 can generally be restored;
– in the savannah, a decrease in the consumption of tree shoots by branch-eating animals (antelopes, giraffes, etc.) leads to the fact that their crowns close. As a result, fires become more frequent and the trees do not have time to recover, the savannah is reborn into thickets of shrubs.\
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 relations "phytophage - plant" leads to the fact that quite often there are short-term outbreaks of the density of phytophage populations and temporary suppression of plant populations, followed by a decrease in the density of phytophage populations.
RELATIONSHIPS "VICTIMS-PREDATOR".
Relationships "predator - prey" represent the links in the process of transfer of matter and energy from phytophages to zoophages or from predators of a lower order to predators of a higher order.
As with the “plant-phytophage” relationship, a situation in which all prey will be eaten by predators, which ultimately will lead to their death, is not observed in nature.
The ecological balance between predators and prey is maintained by special mechanisms that exclude the complete extermination of prey.
So victims can:
- to run away from a predator.
In this case, as a result of adaptation, the mobility of both victims and predators increases, which is especially characteristic of steppe animals, which have nowhere to hide from their pursuers (“Tom and Jerry principle”);
- acquire a protective color (“pretend” as leaves or twigs) or, on the contrary, bright (for example, red, 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 disguise itself in the foliage in summer, and in winter against a white background snow;
– spread in groups, which makes their search and fishing for a predator more energy-intensive;
- hide in shelters;
- switch to active defense measures (herbivores, 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 victims, but also the sense of smell, which allows them to determine the location of the victim by smell.
At the same time, they themselves do everything possible not to reveal their presence. This explains the cleanliness of small cats, which spend a lot of time on the toilet and burying excrement to eliminate the smell.
With intensive exploitation of phytophage populations, people often exclude predators from ecosystems (in the UK, 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 a predator is performed by the person himself, removing a part of the individuals of the phytophage population.
⇐ Previous15161718192021222324Next ⇒
Publication date: 2015-02-18; Read: 6901 | Page copyright infringement
Studopedia.org - Studopedia.Org - 2014-2018. (0.003 s) ...
Competition is a typical phenomenon for wildlife. It is caused by the struggle for resources. But if we talk about intraspecific competition, then it should be noted that this type of competition is most intense.
This is primarily due to the fact that individuals of the same species need some strictly defined resource, which may not be needed by individuals of another species. Therefore, often with this type of competition, there is a depletion of a resource or a certain type of resource.
For example, in a grass mixture consisting of peas and barley, the most fierce competition for soil nitrogen will be between barley plants. This is due to the fact that, due to the ability of peas to fix nitrogen from the air, the need for competition between pea sprouts for nitrogen in the soil is reduced.
Distinguish operational and interference competition.
The first is that all individuals simultaneously exploit resources, but each of them uses only what is left after the competitor. In the second case, one individual does not allow another to occupy the existing habitat and use its resource. Another form of competition is called fierce competition, and the second - rivalry. The first type of competition can lead to the death of the entire population. For example, in the green carrion fly, when the population of larvae on the food source is overcrowded, this type of competition can lead to the fact that at a certain age stage the entire population of offspring will die.
The rivalry is somewhat different. For example, if 150 pairs of birds claim for 100 hollows in some forest, it becomes obvious that 50 pairs will not be able to equip their nests in this area. Therefore, the only possible option for producing offspring can be the migration of these birds to another territory (i.e. emigration).
For a number of reasons, competing individuals of the same species are not equal in their ability to compete. Therefore, in nature, the strongest survive or the one who is more fortunate due to a combination of circumstances. So, the most common sprout, which has risen a little earlier than its fellow tribesmen, will further obscure undersized specimens.
Ignorance of the laws associated with intraspecific competition can lead to sad consequences. For example, in agricultural production, a significant excess of seed sowing rates per unit area can lead to a complete loss of the crop. Exhausted by competition, numerous plants will simply not be able not only to produce a crop, but even to survive to reproductive age.
Competition is directly related to such a concept as an ecological niche, which is not only certain environmental conditions to which an organism is adapted, but also a way of life and a way of obtaining food. Often this term is applied mainly to interspecific competition, but in fact, the ecological niche is characteristic even for each individual organism of the same species.
Another interesting factor in intraspecific competition is the body size of organisms. So, the growth of fish does not stop even after reaching puberty, and is determined by food reserves. The American ecologist R. Whittaker gives an example of this. There are two identical ponds. In the first pond, 100 fry are released, and in the second - 50. As a result, after an equal period of time, the size of the fish in the first pond can be half that in the second. However, the weight of fish in both the first and second ponds may be approximately the same.
In addition to the monotonous depletion of resources, intraspecific competition can also lead to intoxication of the entire population. This is because the excretory products of organisms of the same species are, in fact, poison for them. For example, in a plant community, the root secretions of some plant species can be nutrients for other plant species. Therefore, in the wild, it is not often possible to find communities represented by a single species.
Even grandfather Darwin in his evolutionary theory noted that the severity of the struggle for existence is most pronounced among representatives of one species. And although in the field of recent achievements in genetics and a number of other biological sciences, an increasing number of remarks and claims arise to the theory of Charles Darwin, nevertheless, so far no one has come up with anything more significant in biology.
According to the Ukrainian ecologist V. Kucheryavy: “Intraspecific competition has many negative consequences. It not only impoverishes resources and leads to environmental intoxication, but also promotes self-aggression and cannibalism, social and reproductive failure.”
The above quote willy-nilly evokes associations with human society. There was a time when analogies of the laws of nature with relationships within human society led a number of thinkers to create such a doctrine as social Darwinism, which, according to the ecophilosopher M. Bookchin, "connected all the wild features of civilization with our genetic constitution." According to this doctrine, property inequality in society is explained as interspecific competition between individuals of one species of one population.
And geopolitical inequality between states is explained as intraspecific competition between populations of the same species.
At first glance, everything is correct. However, if we take social Darwinism seriously, then it turns out that a reasonable person, in fact, is not such, but is a typical biological species. It is obvious that this is not the case. But the main flaw of this teaching is that it does not try to change something in better side, and tries not so much to explain as to justify the existing state of affairs. Social Darwinism does not reflect the most important thing - the future perspective. Indeed, in the current environmental realities, it becomes clear that both intraspecific and interspecific human competition depletes the resources of the biosphere so much that it undermines the biological diversity of the entire global ecosystem, and therefore threatens the human species itself.
In modern biological science, scientists are increasingly paying attention not to competition, but to mutual assistance and cooperation. But more on that in one of the next posts. Briefly, we can say the following. Man is a social being, therefore a number of biological laws are leveled due to artificial social institutions and established norms of behavior. At the same time, one should not underestimate the biological laws in the life of the human species. It can be said that many social mechanisms are only a means that simply delays the reaction of biological laws. And as soon as this mechanism is destroyed due to spontaneous, competitive or resource overload, then the biological laws of survival manifest themselves in their entirety.
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 import from North America 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 E. Mayr (1968) notes, 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 pressure of predators played a decisive role in this case is the disappearance of the polar hare from those areas where the mountain hare did not penetrate, but which, due to the nature of the vegetation, are convenient for chasing hares at a trot. Thus, the hypothesis of competitive exclusion in this case, although not completely rejected, should have given way to a hypothesis that takes into account the relationship of three species: two potential competitors and one predator.
Coexistence of competing species. Models of dynamics determined by the concentration of resources
If there are very few reliably proven cases of competitive displacement of one species by another in natural conditions, and there are endless discussions about the importance of competition as a factor determining the dynamics of populations and communities, then in themselves numerous facts of the coexistence of ecologically close and therefore most likely competing species do not raise doubts. . So, 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, in different species that depend on one resource, the values of threshold concentrations may not coincide, but if the resource in environment a lot, then both species grow at maximum rates, and the species that has a greater difference in birth rate and mortality at a given concentration (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 direct isocline on the graph under consideration 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.
Let's now 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 data obtained, he constructed zero growth isoclines for them depending on the concentration of two irreplaceable resources - phosphorus and silicon (Fig. 60).
Within the framework of this model, it is relatively easy to explain the coexistence of different species if they are limited by different resources. However, the very concept of “different resources” needs to be clarified. So, probably, everyone will agree that different types of plants for phytophagous animals can be considered as different resources. With somewhat lesser grounds, but, apparently, one can also say that different parts of one plant can be interpreted as different resources. However, the amount of mineral nutrients needed by plants along with light and moisture is very limited. In any case, it is much less than the number of 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 big number 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 resource equilibrium point is just the intersection point of the isoclines. On fig. 62 shows the consumption vectors (and the supply vectors that continue them) emanating from the equilibrium point. The coexistence of species in this case is stable, since each of the competing species consumes to a greater extent the resource that more restricts the growth of its own population. In particular, in fig. 62 type A consumes the second resource more, and type B - the first. If the situation were reversed, then the coexistence of species would be unstable. Referring to the diagram shown in Fig. 62, where the numbers indicate individual areas 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 from the idealized model to nature, we will find that even closely spaced 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 ensure the real possibility of the coexistence of a large number of species at once (in any case, much more than the number of limiting resources ). Another curious conclusion follows from this: when the environment is enriched with resources, we have the right to expect a decrease in species diversity. Such a reduction in the number of species and an increase in the numerical predominance of a few species are indeed observed both in the aquatic environment (the phenomenon of eutrophication) and in the terrestrial environment (depletion of the species composition of meadows with long-term fertilization).
Conclusion
In nature, any population of a species of organisms enters into a network of relationships with populations of other species: Predator-prey (or resource-consumer) relations and competitive relations are one of the most important in the life of any organism and at the same time one of the most studied. With an increase in the number of prey, both a functional response of the predator (i.e., an increase in the number of prey consumed per unit of time by one individual of the predator) and a numerical one (i.e., an increase in the size of the predator population) are observed. Owing to the ability of predators to react functionally and numerically, their pressure on the prey population acts as a density-dependent factor and therefore has a regulatory effect.
According to the theory developed by mathematicians, the system of interconnected predator and prey populations should most likely demonstrate an oscillatory regime, but even 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 a combination 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, edited by 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 somewhat modified definition of ecology proposed by the Australian researcher G. Andrewartha (Andrewartha. 1961), who, in turn, proceeded from ideas developed back in the 20s. C. Elton (1934; Elton, 1927).
A similar situation was observed, however, in physics. As Weiskopf (1977) noted, the progress made by this science in modern times is associated with the abandonment of attempts to establish at once the whole truth and explain the entire universe. Instead of asking general questions and getting specific answers, scientists began to ask more specific questions, but, surprisingly, they got more general answers.
Note that the expressions “sufficiently perfect” or “sufficiently adapted” do not mean at all that this species is adapted in the best way, and there is nowhere for it to improve further. It also does not follow from what has been said that each species lives in nature under the most optimal conditions. It often happens that from the most optimal (according to abiotic conditions) parts of its potential range, a species is forced out by competitors or predators. It is enough to refer at least to the above example with St. Chrysolina.
In the English-language literature devoted to the evolutionary aspects of ecology, the English proverb “Jack of all trades is a master of none” is very often quoted, which can be roughly translated into Russian as follows: “He who undertakes to do any job does not do any of them well ".
Taxonomic specialists notice (Skvortsov, 1988) that certain names of taxonomic categories are rather proper names, rather than common nouns. For example, when we say “class of monocots” or “class of reptiles”, we first of all imagine monocots and reptiles, and not a certain “class in general” - a conventional unit of taxonomists who agreed that classes are divided into orders, and united into types.
Among domestic scientists, this point of view was defended by S. S. Schwartz (1969). A. V. Yablokov (1987) is currently holding a close opinion, who in his book “Population Biology” defines a population as “... a minimal self-reproducing group of individuals of the same species, inhabiting a certain space for an evolutionary long time, forming an independent genetic system and forming its own ecological space” (p. 150). Explaining his definition, A. V. Yablokov emphasizes that “... a population is always a fairly large group of individuals, over a large number of generations, to a high degree isolated from other similar groups of individuals” (p. 151).
Clones are usually called groups of individuals descended from one ancestral form by vegetative or parthenogenetic reproduction and therefore are very close relatives. Ecologists often use clones of algae, protozoa, rotifers and other organisms in their experiments.
Phytocenologists often adhere to this point of view with particular strictness. Instead of the term "population", they prefer to use the term "coenopopulation", thus 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).
The world of wildlife is surprisingly diverse. The same can be said about the relationship between all the species that inhabit the planet. Just like people, animals can exploit, interfere in each other's affairs, or not interact at all. Examples of competition in nature are a fairly common and natural phenomenon. Which of them are the most striking and interesting?
Examples of competitive relations in nature
Interspecific competition has always been difficult to demonstrate in the field and therefore not many concrete examples can be observed. Just because two species share the same resource does not mean they are competing. Animals simply do not have to fight where everything that is necessary for survival is available in unlimited quantities. Similar examples can be found in natural systems.
To say that species compete, they must occupy the same ecosystem and use a common resource, and as a result this should lead to a decrease in the number of one of the populations, or even to its complete destruction or expulsion. As a rule, it is much easier to demonstrate interference competition. This is when one species directly prevents another species from accessing a limited resource, and this results in reduced survival.
One example of the competition of organisms in nature is the Argentine ant. It is native to South America and is one of the worst invasive ant species in the entire world. When a colony finds a food resource, they physically and chemically defend it, preventing the native ants from accessing the food resource. They often attack and drive out other brethren colonies in the area. This leads to a decrease in the number of ant populations. Because they physically interact with other ant colonies, this is a classic example of interspecific competition in nature.
Invisible competition
It is much more difficult to find examples of competition in nature in animals that do not directly interact with each other. Turtles only eat shrubs that they can reach by stretching their necks. Goats also eat bushes, but they have a wider choice than turtles. As a result, the second gets less vegetation, which is necessary for survival and prosperity. This example of interspecific competition in nature proves the fact that some animals can reduce the number of others even without direct physical interaction.
Exploitation and intervention (interference)
Interspecific competition occurs when different types species in an ecosystem compete for the same resources: food, shelter, light, water, and other essential needs. Such struggle can reduce the abundance of a particular species, moreover, an increase in the population of competitors also tends to limit the growth of a particular species. Thus, competition can be carried out in two ways at the level of individual organisms, namely: exploitative competition and interference competition.
Examples of competition in nature of the first type include the often invisible competition for limited resources. As a result of their use by a certain species, they become insufficient for others. Intervention or interference means direct interaction to obtain resources.
Examples of intraspecific competition in nature, as well as interspecific competition, may include the struggle between predators for prey. So, there can be a fierce confrontation within a species (between two tigers), and between several species (between a lion and a hyena).
Possible effects
- As a result, there may be limits to population sizes, as well as changes in communities and species evolution.
- According to the principle of competitive exclusion, no two species using the same limited resources in the same way and in the same space can exist together.
- While local extinction is rare compared to competitive exclusion and niche differentiation, it also happens.
Examples of competitive relationships
In a dense forest, interspecific competition may occur between treelike plants. This is due to the fact that when mixed species trees, some may have easier access to resources than others. For example, taller trees are able to absorb more sunlight, making it less available to lower tree species.
Wild animals such as lions and tigers are also prime examples of competition in nature. They hunt for the same prey, which may cause less availability of food resources for one of them. In addition, spotted hyenas compete with the African lion for food. The same thing happens with brown bears and tigers. Zebras and gazelles fight for grass.
Competitive relationships can be seen in the oceans, such as sponges and corals vying for space. In desert areas, the coyote and the rattlesnake fight fiercely for food and water. Interspecific competition is also seen in small animals such as squirrels and chipmunks, which tend to compete for nuts and other foods.
Where both organisms live in the same niche and are in competition for resources or space, there will inevitably be a negative outcome for each organism, since the available resource for both parties will decrease.
Intraspecific struggle for existence
This competition is the most fierce and especially stubborn. This confrontation involves the oppression and violent displacement, expulsion or destruction of less adapted individuals. Nature does not like the weak in the struggle for resources and living space. One of the most bloody are the fights for the female during the mating season.
Examples of competition in nature can be very different, including competition in choosing a sexual partner for procreation (deer), the struggle for living space and food (a stronger crow pecks a weak one), and so on.
Interspecies struggle for existence
If individuals of different species fight for something directly or indirectly, then here we are talking about interspecies competition. A particularly stubborn confrontation is observed between closely related creatures, for example:
- A gray rat displaces black from its living space.
- The mistletoe thrush causes a decrease in the population of the song thrush.
- The Prussian cockroach successfully surpasses and infringes on the black relative.
Competition and the struggle for existence are important driving forces of evolution. An important role is played by natural selection and hereditary variability. It is difficult to imagine how diverse and complex are the relationships between living beings that inhabit our planet. Intraspecific and interspecific competition are of great, if not decisive, importance in the formation of biological diversity and the regulation of the size of populations.
Types of interaction between two views
The essence of interspecific competition lies in the fact that individuals of one species have reduced fertility, survival or growth rate as a result of resource use or interference from individuals of another species. However, behind this simple formulation lies a large number of very diverse nuances. The influence of interspecific competition on the population dynamics of competing species is many-sided. Dynamics, in turn, can influence the distribution of species and their evolution.
All these types of interactions are shown in Table 1.
Table 1 Analysis of interactions between populations of two species
|
Type of interactions |
General nature of interaction |
||
|
1. Neutralism |
Neither population affects the other |
||
|
2. Competition |
Direct mutual suppression direct both types |
||
|
3. Competition |
Indirect suppression in case of shortage of a shared resource |
||
|
4. Amensalism |
Population 2 suppresses population 1, but is itself not adversely affected. |
||
|
6 Predation |
Predators are usually larger than prey |
||
|
7. Commensalism |
Population 1, the commensal benefits from overeating; population 2 this merger is indifferent |
||
|
8. Protocooperation |
The interaction is favorable for both species, but not necessarily |
||
|
9. Mutualism |
The interaction is favorable for both species and is mandatory |
- 1. 0 means no significant interactions; + means improved growth, survival, and other benefits to the population (a positive term is added to the growth equation); - means a slowdown in growth and deterioration in other characteristics (a negative term is added to the growth equation).
- 2. Types 2-4 can be considered "negative relationships", types 7-9 - "positive relationships", and types 5 and 6 can be attributed to both of these groups.
Three principles based on these categories should be emphasized:
- · Negative interactions appear at the initial stages of community development or in disturbed natural conditions, where high mortality is neutralized by r-selection.
- In the process of evolution and development of ecosystems, there is a tendency to reduce the role of negative interactions at the expense of positive ones that increase the survival of interacting species
- • Newly formed or new associations are more likely to have strong negative interactions than old associations.
Effect on growth rate or mortality
One population often affects the growth rate or mortality of another. Thus, members of one population may eat members of another population, compete with them for food, release harmful substances, or interact with them in other ways. In the same way, populations can be useful to each other, and the benefit in some cases is mutual, and in others - one-sided. As shown in Table 1, interactions of this kind fall into several categories.
To clarify the action of various factors in complex natural situations, as well as to more accurately define concepts and make reasoning clearer, it is useful to use "models" in the form of equations. If the growth of one population can be described by an equation, then the effect of another population can be expressed by a term that changes the growth of the first population. Depending on the type of interaction, different terms can be substituted into the equation. For example, in the presence of competition, the growth rate of each population is equal to the rate of unlimited growth minus the influence of its own abundance (which increases with the growth of the population) and minus the value characterizing the negative influence of another species, N2 (which also increases as the numbers of both species N1 and N2 increase). ), or
growth rate;
Unlimited growth;
Influence of own numbers;
Negative influence of another kind.
When the species of two interacting populations have a beneficial rather than a damaging effect on each other, a positive term is introduced into the equation. In such cases, both populations grow and prosper, reaching equilibrium levels, which is beneficial for both species. If for the growth and survival of each of the populations their mutual influence on each other is necessary, then such relationships are called mutualism. If, on the other hand, these favorable influences only cause an increase in the size of the population or the rate of its growth, but are not necessary for its growth and survival, then such an interaction corresponds to cooperation or proto-cooperation. (Since such cooperation is not the result of conscious or "intelligent" activity, it is preferable to use the latter term.) Both mutualism and protocooperation lead to a similar result: population growth in the absence of the other is either slowed down or equal to zero. Upon reaching equilibrium, both populations continue to coexist, usually maintaining a certain ratio.
Competition and coexistence of species
In the broadest sense, competition is the interaction of two organisms seeking to obtain the same resource. Interspecific competition is any interaction between populations of two or more species that adversely affects their growth and survival. As shown in Table 1, it can appear in two forms. The tendency towards ecological separation observed when closely related or otherwise similar species compete is known as the principle of competitive exclusion. At the same time, competition contributes to the emergence of many adaptations in the process of selection, which leads to an increase in the diversity of species that coexist in a given space or community.
Competitive interactions may involve space, food or nutrients, light, unused substances, dependence on predators, exposure to disease, etc., and many other types of interactions. The results of the competition are of great interest; they have been repeatedly investigated as one of the mechanisms of natural selection.
Interspecific competition, no matter what it is based on, can either lead to an equilibrium between two species, or, with more severe competition, to the replacement of a population of one species by a population of another, or to one species crowding out another in another place. or force him to switch to the use of other food. It has been repeatedly noted that closely related organisms that lead a similar way of life and have a similar morphology do not live in the same places. If they live in the same place, they often use different resources or are active at different times.
The explanation for the ecological separation of closely related (or otherwise similar) species has come to be known as the Gause principle, after the Russian biologist who in 1932 first confirmed its existence experimentally or as a principle of competitive exclusion (Harden, 1940).
To understand the causes of competition, it is necessary to consider not only the characteristics of populations and the conditions that determine competitive exclusion, but also situations in which similar species coexist, since in open natural systems a large number of species actually use common resources. The table shows a situation that could be called the Tribolium (hrushchaki) - Trifolium (trefoil) model; this model clearly demonstrates the competitive exclusion in a pair of beetle species (Tribolium) and the coexistence of two clover species (Trifolium).
One of the most rigorous and lengthy experimental studies of interspecific competition was conducted in the laboratory of Dr. Thomas Park at the University of Chicago. Park and his students and staff have worked with mealworms, in particular species of the genus Tribolium. These small beetles can complete their entire life cycle in a very simple and homogeneous environment - in a jar of flour or wheat bran. In this case, the environment serves both as food and as a habitat for larvae and adults. By adding fresh media regularly, the beetle population can be maintained. for a long time. From the point of view of energy flow concepts, such an experimental system can be described as a stabilized heterotrophic ecosystem in which food energy import is balanced by respiration costs.
Table 2. Case of competitive exclusion in mealworm (Tribolium) populations. (According to Park, 1954).
1. Each of the 6 variants of experiments was carried out in 20 - 30 repetitions. In a pure culture, each species survives under any combination of conditions, but when two species are cultivated together, only one survives. The percentage expresses the relative number of repetitions in which only one species was preserved, while the other disappears.
Using the data obtained in model experiments on Tribolium, it is easy to create conditions in which species would not exclude each other, but coexist. If crops are placed alternately between hot and humid and dry and cold conditions (to simulate seasonal changes in the weather), the advantage of one species over the other will not be long enough to destroy the other. If the culture system were "open" and individuals of the dominant species were forced to emigrate (or removed, as predators do) quickly enough, then competition would be so weak that both species could coexist. Many other conditions could also favor existence.
Interesting experiments on competition in plants were carried out by J. L. Harper and his colleagues at the University College of North Wales. Due to differences in the nature of growth, two types of clover can coexist in the same environment (under the same lighting conditions, temperature, on the same soil, etc.). Of these two species, Trifolium repens grows faster and reaches its maximum leafiness sooner. However, T. fragiferum has longer petioles and higher set leaves, so it can move to the topstory earlier than the fast growing species (especially after T. repens' growth rate has waned) and thus avoid shading. In mixed grass stands, due to these features, each species inhibits the development of the other, but both of them are able to complete the life cycle and produce seeds, although the density of each species is reduced (however, the total density in mixed grass stands of the two species was approximately equal to the density in pure grass stands) . In this case, both species, despite strong competition for light, can coexist, and this coexistence is due to morphological features and differences in the time of maximum growth. Harper (Naggreg, 1961) concluded that two plant species can coexist for a long time if their populations are independently regulated by one or more of the following mechanisms: 1) differences in nutritional requirements (eg, legumes and non-legumes); 2) differences in the causes of mortality (for example, different sensitivity to grazing); 3) sensitivity to different toxins; and 4) sensitivity to the same regulatory factor (light, water, etc.) at different times (as in the case of the clover example just described).
In examining the literature on competition, the general impression is that in systems where immigration and emigration are absent or reduced, competition is fiercer and competitive exclusion is more likely. Such systems include laboratory cultures, islands, or other natural situations with insurmountable barriers to entry and exit. In ordinary natural open systems, the probability of coexistence is higher.
An example of competition with direct suppression is described by Crombie (1947). He found that co-cultivation in flour of Tribolium and Oryzaephilus (another genus of mealworms) ends up killing Oryzaephilus because Tribolium is more aggressive in cultivating immature stages of Oryzaephilus.
However, if glass tubes are placed in the flour, in which immature individuals of the smaller Oryzaephilus can hide, then both populations will survive. Thus, if there are shelters in the environment that allow one to hide from direct influence (in this case, predation), then competition is reduced so much that both species are preserved.
But enough laboratory examples. It is clear that crowding in laboratory experiments can be quite significant, leading to excessive competition. In field studies, interspecific competition has been studied in detail in plants; the results of these studies led to the conclusion (at present, this conclusion is generally accepted) that competition is an important factor causing the change of species. Keever (Keever, 1955) described the case when the fallow of the first year was almost entirely occupied by a pure herbage of a high weed, later it was gradually replaced from here by another species, previously not known in these places. These two species, although they belong to different genera, have very similar life cycles (the time of flowering and seed maturation) and life forms, fell into conditions of intense competition. Careful subsequent studies of these fallow fields showed that the newcomer did not crowd out the previously growing species; it turned out that both species coexist, but their numerical ratio depends on the soil, time and degree of disturbance.
The following example concerns two species of terrestrial salamanders, Plethodon glutinosus and P. jordani, found in the southern Appalachian Mountains in the United States.
P. jordani is usually found at higher altitudes than P. glutinosus, but in some areas their ranges overlap. Hairston (1980) experimented on two sites, one in the Great Smoky Mountains, where overlap was observed only over a small range of altitudes, and the other in the Balsam Mountains, where the species coexisted over a much wider area. Both sites were inhabited by populations of both species and, in general, the salamander fauna was similar; the populations were at the same altitude and were subjected to the same influences. At each site
Hairston set up seven experimental plots: P. jordani specimens were removed from two of them, P. glutinosus specimens were removed from the other two, and the remaining three served as controls. This work was started in 1974, and over the next 5 years, the number of individuals of each species was counted 6 times a year at all sites; All individuals were divided into three groups: one-year-olds, two-year-olds, and all the rest.
On the control plots, as expected, P. jordani was much more numerous of the two species under consideration; and on the sites from which it was removed, a statistically significant increase in the abundance of P. glutinosus was observed. The sites from which P. glutinosus was removed did not show a corresponding significant increase in P. jordani abundance. However, in both plots, a statistically significant increase in the proportion of P. jordani among yearlings and two year olds was observed. Apparently, this was due to increased fecundity and (or) increased survival of juveniles; both of these factors are the main reasons that determine the rate of reproduction.
An important point is that individuals of both species initially experienced adverse effects from another species; after the removal of one of their species, the remaining one showed a significant increase in the number and (or) fertility and (or) survival. It follows that in the control plots and in other places of joint habitat, these species usually competed with each other, but still coexisted.
As another example, I will cite an experiment performed by one of the most famous "founding fathers" of plant ecology, A.G. Tansley, who studied competition between two species of bedstraw (Tansley, 1917). Galium hercinicum is a species that grows in the UK on acidic soils, while Galium pumilum is limited to more alkaline soils.
Growing the species separately, Tensley found that each of them grew well in both the acidic soil from the Galium hercinicum locality and the alkaline soil from the Galium pumilum locality. However, only Galium hercinicum grew successfully in acidic soil, and Galium pumilum in alkaline soil. Apparently, these results indicate competition between species when they are grown together. In the competitive struggle, one species wins, while the other loses so much that it is forced out of the biotype. The outcome of competition depends on the conditions in which it occurs.
