In nature, everyone existing view is a complex complex or even a system of intraspecific groups that cover individuals with specific features of structure, physiology and behavior. Such an intraspecific association of individuals is population.

The word "population" comes from the Latin "populus" - people, population. Hence, population- a set of individuals of the same species living in a certain territory, i.e. those that only interbreed with each other. The term "population" is currently used in the narrow sense of the word when talking about a specific intraspecific grouping inhabiting a certain biogeocenosis, and in a broad, general sense - to refer to isolated groups of a species, regardless of what territory it occupies and what genetic information it carries.

Members of the same population affect each other no less than the physical factors of the environment or other species of organisms living together. In populations, to one degree or another, all forms of relationships characteristic of interspecific relations are manifested, but the most pronounced mutualistic(mutually beneficial) and competitive. Populations can be monolithic or consist of subpopulation level groupings - families, clans, herds, flocks and so on. Combining organisms of the same species into a population creates qualitatively new properties. Compared to the lifetime of an individual organism, a population can exist for a very long time.

At the same time, a population is similar to an organism as a biosystem, since it has a certain structure, integrity, a genetic program for self-reproduction, and the ability to autoregulate and adapt. The interaction of people with species of organisms that are in the environment, in the natural environment or under the economic control of man, is usually mediated through populations. It is important that many patterns of population ecology also apply to human populations.

population is the genetic unit of a species, the changes of which are carried out by the evolution of the species. As a group of individuals of the same species living together, the population acts as the first supraorganismal biological macrosystem. The adaptive capacity of a population is much higher than that of its constituent individuals. A population as a biological unit has certain structure and functions.

Population structure characterized by its constituent individuals and their distribution in space.

Population functions similar to the functions of other biological systems. They are characterized by growth, development, the ability to maintain existence in constantly changing conditions, i.e. populations have specific genetic and ecological characteristics.

Populations have laws that allow the limited resources of the environment to be used in this way to ensure that offspring are left. Populations of many species have properties that allow them to regulate their numbers. Maintaining optimal population under given conditions is called population homeostasis.

Thus, populations, as group associations, have a number of specific properties that are not inherent in each individual. The main characteristics of populations: number, density, birth rate, mortality, growth rate.

Populations are characterized by a certain organization. The distribution of individuals over the territory, the ratio of groups by sex, age, morphological, physiological, behavioral and genetic characteristics reflect population structure. It is formed, on the one hand, on the basis of the general biological properties of the species, and on the other hand, under the influence of abiotic environmental factors and populations of other species. The structure of populations, therefore, has an adaptive character.

The adaptive possibilities of a species as a whole as a system of populations are much broader than the adaptive features of each particular individual.

Population structure of the species

The space or range occupied by a population may be different for both different types and within the same species. The range of a population is largely determined by the mobility of individuals or the radius of individual activity. If the radius of individual activity is small, the size of the population range is usually also small. Depending on the size of the territory occupied, it is possible to distinguish three types of populations: elementary, ecological and geographical (Fig. 1).

Rice. 1. Spatial subdivision of populations: 1, range of the species; 2-4 - respectively geographical, ecological and elementary populations

There are sex, age, genetic, spatial and ecological structure of populations.

The sexual structure of the population represents the ratio of individuals of different sexes in it.

Age structure of the population- the ratio in the composition of the population of individuals of different ages, representing one or different offspring of one or several generations.

Genetic structure of the population is determined by the variability and diversity of genotypes, the frequency of variations of individual genes - alleles, as well as the division of the population into groups of genetically close individuals, between which, when crossing, there is a constant exchange of alleles.

The spatial structure of the population - the nature of the placement and distribution of individual members of the population and their groups in the area. The spatial structure of populations differs markedly between sedentary and nomadic or migratory animals.

Ecological structure of the population is the division of any population into groups of individuals interacting differently with environmental factors.

Each species, occupying a certain territory ( range) is represented on it by a system of populations. The more complex the territory occupied by a species is dissected, the more opportunities there are for the isolation of individual populations. However, to a lesser extent, the population structure of a species is determined by its biological characteristics, such as the mobility of its constituent individuals, the degree of their attachment to the territory, and the ability to overcome natural barriers.

Isolation of populations

If the members of a species constantly mix and mingle over vast areas, such a species is characterized by a small number of large populations. With poorly developed abilities for movement, many small populations are formed in the composition of the species, reflecting the mosaic nature of the landscape. In plants and sedentary animals, the number of populations is directly dependent on the degree of heterogeneity of the environment.

The degree of isolation of neighboring populations of the species is different. In some cases, they are sharply separated by uninhabitable territory and clearly localized in space, such as populations of perch and tench in isolated lakes.

The opposite variant is the continuous colonization of large territories by the species. Within the same species, there can be populations with both well-defined and blurred boundaries, and within a species, populations can be represented by groups of different sizes.

Relationships between populations support the species as a whole. Too long and complete isolation of populations can lead to the formation of new species.

Differences between individual populations are expressed to varying degrees. They can affect not only their group characteristics, but also the qualitative features of the physiology, morphology and behavior of individual individuals. These differences are created mainly under the influence of natural selection, which adapts each population to the specific conditions of its existence.

Classification and structure of populations

An obligatory sign of a population is its ability to exist independently in a given territory for an indefinitely long time due to reproduction, and not the influx of individuals from outside. Temporary settlements of different scales do not belong to the category of populations, but are considered intrapopulation subdivisions. From these positions, the species is represented not by a hierarchical subordination, but by a spatial system of neighboring populations of different scales and with varying degrees of connections and isolation between them.

Populations can be classified according to their spatial and age structure, density, kinetics, habitat persistence or change, and other ecological criteria.

The territorial boundaries of populations of different species do not coincide. The diversity of natural populations is also expressed in the variety of types of their internal structure.

The main indicators of the structure of populations are the number, distribution of organisms in space, and the ratio of individuals of different quality.

The individual features of each organism depend on the characteristics of its hereditary program (genotype) and on how this program is realized in the course of ontogenesis. Each individual has a certain size, gender, distinctive features morphology, behavioral features, their limits of endurance and adaptability to environmental changes. The distribution of these traits in a population also characterizes its structure.

The structure of the population is not stable. The growth and development of organisms, the birth of new ones, death from various causes, changes in environmental conditions, an increase or decrease in the number of enemies - all this leads to a change in various relationships within the population. The direction of its further changes largely depends on the structure of the population in a given period of time.

Sexual structure of populations

The genetic mechanism of sex determination provides for the splitting of offspring by sex in a ratio of 1: 1, the so-called sex ratio. But it does not follow from this that the same ratio is characteristic of the population as a whole. Sex-linked traits often determine significant differences in the physiology, ecology, and behavior of females and males. Due to the different viability of the male and female organisms, this primary ratio often differs from the secondary and especially from the tertiary ratio, which is characteristic of adults. So, in humans, the secondary sex ratio is 100 girls to 106 boys, by the age of 16-18 this ratio is leveled off due to increased male mortality and by the age of 50 it is 85 men per 100 women, and by the age of 80 - 50 men per 100 women.

The sex ratio in a population is established not only according to genetic laws, but also to a certain extent under the influence of the environment.

Age structure of populations

Birth and death rates, population dynamics are directly related to the age structure of the population. The population consists of individuals of different age and sex. For each species, and sometimes for each population within a species, its own ratios of age groups are characteristic. In relation to the population, they usually distinguish three ecological ages: pre-reproductive, reproductive and post-reproductive.

With age, the requirements of an individual to the environment and resistance to its individual factors naturally and very significantly change. At different stages of ontogenesis, a change in habitats, a change in the type of nutrition, the nature of movement, and the general activity of organisms can occur.

Age differences in the population significantly increase its ecological heterogeneity and, consequently, its resistance to the environment. The probability increases that in case of strong deviations of conditions from the norm, at least a part of viable individuals will remain in the population, and it will be able to continue its existence.

The age structure of populations has an adaptive character. It is formed on the basis of the biological properties of the species, but always also reflects the strength of the impact of factors. environment.

Age structure of populations in plants

In plants, the age structure of the cenopopulation, i.e. population of a particular phytocenosis is determined by the ratio of age groups. The absolute, or calendar, age of a plant and its age state are not identical concepts. Plants of the same age can be in different age states. The age or ontogenetic state of an individual is the stage of its ontogenesis, at which it is characterized by certain relationships with the environment.

The age structure of the cenopopulation is largely determined by the biological characteristics of the species: the frequency of fruiting, the number of produced seeds and vegetative primordia, the ability of vegetative primordia to rejuvenate, the rate of transition of individuals from one age state to another, the ability to form clones, etc. The manifestation of all these biological features, in turn, depends on the conditions external environment. The course of ontogenesis also changes, which can occur in one species in many variants.

Different plant sizes reflect different vitality individuals within each age group. The vitality of an individual is manifested in the power of its vegetative and generative organs, which corresponds to the amount of accumulated energy, and in resistance to adverse effects, which is determined by the ability to regenerate. The vitality of each individual changes in ontogenesis along a single-peak curve, increasing on the ascending branch of ontogenesis and decreasing on the descending one.

Many meadow, forest, steppe species when grown in nurseries or crops, i.e. on the best agrotechnical background, reduce their ontogeny.

The ability to change the path of ontogenesis ensures adaptation to changing environmental conditions and expands the ecological niche of the species.

Age structure of populations in animals

Depending on the characteristics of reproduction, members of a population may belong to the same generation or to different ones. In the first case, all individuals are close in age and approximately simultaneously go through the next stages of the life cycle. The timing of reproduction and the passage of individual age stages are usually confined to a specific season of the year. The size of such populations is, as a rule, unstable: strong deviations of conditions from the optimum at any stage of the life cycle affect the entire population at once, causing significant mortality.

In species with a single reproduction and short life cycles, several generations are replaced during the year.

When human exploitation of natural populations of animals, taking into account their age structure is of paramount importance. In species with a large annual recruitment, a larger part of the population can be removed without the threat of undermining its numbers. For example, in pink salmon, which matures in the second year of life, it is possible to catch up to 50-60% of spawning individuals without the threat of further population decline. For chum salmon that matures later and has a more complex age structure, the removal rates from a mature herd should be lower.

An analysis of the age structure helps to predict the size of the population over the life of a number of next generations.

The space occupied by the population provides it with the means of subsistence. Each territory can feed only a certain number of individuals. Naturally, the completeness of the use of available resources depends not only on the total size of the population, but also on the distribution of individuals in space. This is clearly manifested in plants whose feeding area cannot be less than a certain limiting value.

In nature, an almost uniform ordered distribution of individuals in the occupied territory is occasionally found. However, most often the members of the population are distributed unevenly in space.

In every specific case the type of distribution in the occupied space turns out to be adaptive, i.e. allows optimal use of available resources. Plants in a cenopopulation are most often distributed extremely unevenly. Often the denser center of the cluster is surrounded by less densely spaced individuals.

The spatial heterogeneity of the cenopopulation is related to the nature of the development of clusters in time.

In animals, due to their mobility, the methods of ordering territorial relations are more diverse than in plants.

In higher animals, intrapopulation distribution is regulated by a system of instincts. They are characterized by a special territorial behavior - a reaction to the location of other members of the population. However, sedentary life is fraught with the threat of rapid depletion of resources if the population density is too high. The total area occupied by the population is divided into separate individual or group areas, which achieves an orderly use of food supplies, natural shelters, breeding grounds, etc.

Despite the territorial isolation of the members of the population, communication is maintained between them using a system of various signals and direct contacts at the borders of possessions.

"Fixing the site" is achieved different ways: 1) protection of the boundaries of the occupied space and direct aggression towards the stranger; 2) special ritual behavior that demonstrates a threat; 3) a system of special signals and marks indicating the occupation of the territory.

The usual reaction to territorial marks - avoidance - is hereditary in animals. The biological benefit of this type of behavior is clear. If the possession of a territory was decided only by the outcome of a physical struggle, the appearance of each stronger alien would threaten the owner with the loss of the territory and elimination from reproduction.

Partial overlap of individual territories serves as a way to maintain contacts between members of the population. Neighboring individuals often maintain a stable mutually beneficial system of connections: mutual warning of danger, joint protection from enemies. Normal animal behavior includes active search contacts with representatives of their own species, which often intensifies during a period of decline in numbers.

Some species form widely nomadic groups that are not tied to a specific territory. This is the behavior of many fish species during feeding migrations.

There are no absolute distinctions between different ways of using the territory. The spatial structure of the population is very dynamic. It is subject to seasonal and other adaptive rearrangements in accordance with place and time.

The patterns of animal behavior are the subject of a special science - ethology. The system of relationships between members of one population is therefore called the ethological or behavioral structure of the population.

The behavior of animals in relation to other members of the population depends, first of all, on whether a solitary or group way of life is characteristic of the species.

A solitary lifestyle, in which the individuals of a population are independent and isolated from each other, is characteristic of many species, but only at certain stages of the life cycle. Completely solitary existence of organisms does not occur in nature, since in this case it would be impossible to carry out their main vital function - reproduction.

With a family lifestyle, the bonds between parents and their offspring are also strengthened. The simplest form of such a connection is the care of one of the parents about the laid eggs: the protection of the masonry, incubation, additional aeration, etc. With a family lifestyle, the territorial behavior of animals is most pronounced: various signals, markings, ritual forms of threat and direct aggression ensure possession of a plot sufficient for rearing offspring.

Larger associations of animals - flocks, herds And colonies. Their formation is based on the further complication of behavioral relationships in populations.

Life in a group through the nervous and hormonal systems is reflected in the course of many physiological processes in the animal's body. In isolated individuals, the level of metabolism noticeably changes, reserve substances are used up faster, a number of instincts do not manifest themselves, and overall viability worsens.

Positive group effect manifests itself only up to a certain optimal level of population density. If there are too many animals, it threatens everyone with a lack of environmental resources. Then other mechanisms come into play, leading to a decrease in the number of individuals in the group through its division, dispersal, or a drop in the birth rate.

In nature, organisms of the same species exist in the form of many populations.

population- this is a set of individuals of the same species, freely interbreeding with each other, inhabiting a certain territory with relatively homogeneous living conditions.

Populations of the same species are relatively isolated groups with certain distribution boundaries. The degree of isolation of populations depends on the ability of the species to disperse, migration, and geographical conditions. One species of river perch can live in various fresh water bodies and form different populations. All spruces in the forest form a single population and are isolated from members of their own species in another forest. A population is the structural unit of a species. The main evolutionary processes take place in it, adaptive features are fixed, allowing organisms to adapt to specific living conditions.

In ecology, a population is considered as the main element of any community of living organisms and is characterized by such features as density and abundance, age and sex structure, birth and death rates, and spatial distribution.

Population size. This total number individuals living in a territory or community. Connected with the number density populations - the number of individuals (or biomass) per unit area. For example, 300 hazel bushes per 1 ha of forest, 5 million chlorella specimens per 1 m3 of water. Population density is unstable and fluctuates in different years and seasons. It depends on the migration of individuals, climatic conditions, mortality, availability of resources. In some years, there may be an outbreak in the number of any population.

Spatial structure of the population. It is determined by the characteristics of the distribution of the population in the territory. Often individual individuals form clusters, groups, flocks, "families". With the help of special signals, they mark the occupied area, expelling invading competitors. In birds, singing is used for this, in mammals, the excretion of odorous substances or excrement. Nomadic animals have certain migration routes.

With a sharp increase in numbers, mass migration of individuals sometimes occurs, entailing a change in the spatial structure of the population or the displacement of a competing population of another species.

Fertility. This property characterizes the ability of a population to reproduce, the frequency of the appearance of new individuals per unit of time (the number of young, eggs laid, eggs in animals, seeds and spores in plants). In microorganisms, fertility depends on the rate of cell division. The birth rate is determined by the rate of increase in the population in real conditions.

Mortality. It is characterized by the number of individuals who died in a certain period, i.e., the rate of decrease in the population. The death of individuals at different stages of development is not the same. The mortality of fish at the stage of eggs and fry is much higher than among adults. The stronger the instinct of caring for offspring is developed in animals, the lower the mortality rate of juveniles.

Lack of care for offspring can be compensated for by the high fertility of individuals (fish, amphibians, some insects).

Birth and death rates regulate the size of the population and its age composition.

Age structure of the population. It is determined by the ratio of individuals of different ages, which also fluctuates. In a stable population, the birth rate is equal to the death rate, the population size remains almost unchanged, and age groups are approximately in the same ratio. In growing populations, the birth rate exceeds the death rate, and the numbers increase.

Sex structure. It is determined by the sex ratio, the number of males and females in the population. Populations of different species are heterogeneous in their sex composition. For example, fur seals, seals in the harem of each male have a large number of females. In animals that form pairs, the sex ratio is approximately equal.

Population dynamics. Homeostasis. Population size depends on many factors. Favorable climatic conditions, the availability of a sufficient amount of food, the weakening of predation lead to an increase in fertility and birth rate, and an increase in numbers. And vice versa, lack of food, increased competition, unfavorable conditions reduce the number.

The change in the number of organisms over time is called population dynamics.

Periodic fluctuations are associated with regular measurements of environmental factors, seasonal rhythms. In some years, outbreaks of numbers can occur, while the size of the population increases by 20-40 times without a certain periodicity. This is how population waves arise (Fig. 95).

Rice. 95. Fluctuations in the number of lynx and hare

An important feature of the population is the ability to naturally regulate density. This is ensured by special mechanisms that maintain the population size at a certain level.

The ability of a population to self-regulate to maintain numbers at a certain level is called population homeostasis.

Usually, the population is in a state of dynamic equilibrium, which is achieved by alternating positive and negative feedbacks. With an increase in numbers, food supplies decrease, organisms are in unfavorable conditions, which leads to their mass death and a drop in fertility, i.e., a reduction in the population. The growth of its population stops, food resources are restored, which entails a re-growth of the population. In addition, with increasing density, the probability of propagation increases. infectious diseases leading to the death of some individuals. With a high density of plants, they are under pressure from the "neighbors" (lack of water, light). As a result, the death of some organisms occurs, i.e., the process of "self-thinning". § 70. The relationship of organisms. Biotic environmental factors

1.1 What is a population, composition, structure.

1.2 Population properties.

1.3 Demographic characteristics. Density. Number.

A population is a group of individuals of the same species that have the ability to interbreed freely and maintain their existence in a given habitat for a sufficiently long time.

sustainable existence various kinds Animals and plants require the presence of certain environmental conditions and the necessary resources. When moving from one area to another, both conditions and resources can change; and these changes occur inconsistently. Some factors may change smoothly (for example, temperature when moving from south to north), not change at all (for example, the content of carbon dioxide in the air), or change abruptly (as, for example, happens with changes in the composition and structure of soils). All this leads to the fact that habitats suitable for a particular species are formed in space, as it were, in the form of separate islands. Species populate these habitats - "islands" with their populations.

Consequently, the species are not distributed evenly, but by separate groups of individuals - populations. Individuals of the population, reproducing, develop suitable habitats. Populations of the same species can be separated from each other by clear boundaries. For aquatic organisms, as a rule, the boundaries are along the coastlines of water bodies. In some species, the boundaries between populations are fuzzy, blurred, for example, in plant and animal species that live in the terrestrial-air environment and have a wide geographical distribution. An example is the gray crow, or the hare, because. they are found in various habitats.

Each population has a certain structure - structure. The structure of the population is manifested in a certain quantitative ratio of individuals of different ages, sex and size. There are age, sex, size, genetic structures.

In a population of any plant or animal species, different age groups of individuals are found.

Conventionally, three ecological groups can be distinguished in the population: young (pre-reproductive), mature (reproductive), and old (post-reproductive).

prereproductive- a group of individuals whose age has not reached the ability to reproduce;

reproductive- a group that reproduces new individuals;

post-reproductive- individuals that have lost the ability to participate in the reproduction of new generations.

What groupings do animals form and how are they distributed in space?

Individuals in a population can live alone

can form groups - families

A family is the simplest permanent grouping of individuals, which after the breeding season may disintegrate, or may consist of parents and descendants of several generations: clans in hyena dogs, prides in lions, herds of many primates. Cetaceans, ungulates, primates live, as a rule, in herds.

flocks

herds

or represented by colonies.

A herd is a group of animals of the same species that remain close to each other, behave in the same way. The size of the herd and its composition by age and sex are variable over time. Herds of whales, monkeys include dozens of animals, herds reindeer, saigas, wildebeest form hundreds and thousands of individuals. Animals in the herd learn about the appearance of a predator, the presence of food, a safe path to a watering hole, a shelter by the behavior of the leader of the herd or by the behavior of their neighbors. A flock is a temporary mobile grouping of individuals, insects, fish, birds. Flocks of sedentary birds such as tits occupy a permanent territory and have a hierarchical structure. A pack of wolves consists of 5-10, at most 22 individuals, which include monogamous pairs and several generations of their offspring. The flock is united by a single habitat, where they hunt together. Individuals, families and other groups of individuals actively disperse in space, using various methods of marking and protecting the territory.

Consider how a herd of baboons meets a herd of neighbors on the border of their possessions. Fighting-age males move forward, forming a crescent-shaped formation, stop and assume threat poses. So do the neighbors. The hierarchs pass through the formation and slowly approach the border, peering at the hierarchs of another herd walking towards them. If the meeting took place on the border and the territory is not disturbed, but the herd is familiar, the hierarchs, having recognized each other, converge and embrace. After that, younger males may also meet. The herd of baboons has several dozen heads. When baboons move from place to place, they go in a certain order, which can be called marching formation. In the middle of the herd are old males - dominants. From this position, it is convenient for them to survey the herd and manage it. At the same time, this is the safest place in the herd in case of an unexpected attack by a predator.

Near the dominant males are young females, females carrying cubs younger age, and dependent cubs. On the one hand, this allows you to follow them, and on the other hand, this is the safest place. On the outskirts of the core of the herd is the youth. Ahead of the herd, at a distance of visibility, males of the second rank go in an unfolded chain. Ahead walking individuals occupy the most dangerous place. Faced with a moderately strong predator, they deploy in a crescent and try to delay it, while the herd runs away. Predators prefer not to get involved with males, which are quite strong even one by one, and even more so when they act together.

Behind the herd, also at a distance of visibility, there are males of the third hierarchical rank, not dangerous for the hierarchs. If the herd is traveling over rough terrain and visibility is poor, it may single out one or two groups of individuals to guard the herd from the sides.

The system of signals allows animals to find a mating partner, protect their territory, and ensure the survival of their offspring. Males of many ungulates seize and protect certain areas during the rut. In red deer, the territorial division between males, as it were, is superimposed on the existing long time division of territory between groups of females with young. With their roar, the smell of secretions of odorous glands and urine on the ground, marks on the bark of trees, applied by horns, males signal each other about the occupation of the place, and, if necessary, enter into a duel with an opponent. Deer that have not captured their territory do not have a harem of females. Thus, the number of males participating in reproduction is limited.

Poisonous snakes during a territorial skirmish, they stretch out, stand up, sway, push each other, but they never only never bite, but do not even show weapons. Well-armed animals can threaten each other for a long time, and when one of them gets tired, he abruptly changes his position, exposing the enemy to the most unprotected place to strike. For the enemy, the ban works like an electric shock: all his angry ardor evaporates and he hides his weapon. "He who is greater than you is stronger than you."

People have long thought that birds sing for human pleasure. Now we know that birdsong is a spoken language, a way to mark your territory, to attract the attention of a female. The crowing of a rooster is the territorial sound signal.

During the distribution of territory, during an aggressive skirmish, the animal, which assessed the enemy as a larger one, recognizes a psychological defeat, and there may be no further struggle - one yields to the other. If it comes to fighting, then in many species the goal is the same - to humiliate the enemy: to knock down or throw to the ground. The fall is sometimes accompanied by physical injury, but it can also be completely painless, like snakes dropping each other. It's still a defeat and the loser concedes.

The loser in the dispute "lays down his weapons" (thorns, tufts, teeth, horns), hides them so as not to frighten the winner. Many animals fall and turn upside down.

Many species of animals are so armed that a skirmish between rivals would end in the death of one or both of them. Therefore, animals have developed such forms of behavior, which are called instinctive prohibitions, or natural morality: in the behavior of animals, innate prohibitions are observed: “do not kill”, “do not beat the lying”, i.e. an opponent who has assumed a pose of humility, do not touch the cubs, do not encroach on someone else's territory, someone else's nest, someone else's female, do not attack unexpectedly or from behind, do not take away food, do not steal it. Such prohibitions are called biological morality.

And what is the fate of individuals who could not hold on to the territory? Their destiny is to remain lonely, they are not included in the process of reproduction and die faster than their more fortunate counterparts in the population.

A special role in the herd is occupied by old individuals. Surrounded by enthusiastically looking cubs, the old baboon shows how to dig in the ground, tear apart rotten stumps, turn over stones, crack nuts, dig for water and do many other things that he was taught in childhood and that he himself comprehended in a long life.

In herd animals, the mother-child relationship plays a special role. The birth of a cub, caring for it in many animals is a serious problem. In order for the newborn deer to remember the mother well, the female retires during calving. The first thread that connects mother and calf is the smell of a calf. The mother licks the baby, she is attracted by the smell of amniotic fluid. Mother and calf alone. Mother screams for two hours, then stops. And now, in the herd, the calf confidently distinguishes the mother's voice from the voices of other deer. The deer is endowed with an innate reaction to move towards a large dark object, i.e. to mother. Once under his mother, he tosses his head. This reaction helps to find the udder. The mother licks the deer, and he tries to stand with his head to the mother. Not a single movement of mother and fawn is accidental.

What is the main function of a population? Only a population can tirelessly reproduce new generations of a species in a particular ecosystem. Individuals of different sexes of populations of the same species find each other, while individuals of closely related species are reproductively isolated and cannot interbreed (Fig. 7).

The main properties of populations:

Self-reproduction. Populations are able to maintain their existence indefinitely in a given habitat and be stable groupings of individuals of a given species in time and space. The term "population" is not applicable to a flock of fish or sparrows, since they can easily decay under the influence of external factors or mix with others and are not able to reproduce themselves sustainably. Large groups possess the main properties of the species and are represented by all categories of its constituent individuals, for example, all perch individuals in a lake or all pine trees in a forest.

Heredity provides interrelation of generations in population.

Variability. The complex of conditions in different habitats is not the same. Influenced different conditions properties that distinguish them from each other can arise and accumulate in individual populations, which is manifested in small deviations in the structure of organisms belonging to different populations, their physiological parameters and other characteristics.

Thus, populations, like individual organisms, are subject to variability.

Variability, the most important factor in evolution. Population variability increases the internal diversity of the species, which increases the resistance of the species to local (local) changes in living conditions, allows it to penetrate and gain a foothold in new conditions and areas. From which it follows that existence in the form of populations enriches the species, ensures its integrity and self-regulation of the main species properties. It is thanks to the functioning of populations that the conditions conducive to the maintenance of life are created.

demographic indicators. Population characteristics - abundance, fertility, mortality, age composition, are called demographic indicators. Knowing them is very important for understanding the laws that govern the life of populations and predicting the constant changes taking place in them.

The study of demographic indicators is of great practical importance, for example, in order to properly plan the intensity of felling during timber harvesting, it is very important to know the rate of forest restoration. Some animal populations are used to obtain valuable food or fur raw materials. The study of others is important from a health point of view, for example, populations of small rodents, among which pathogens of diseases dangerous to humans circulate.

First of all, we are interested in changes in both the population as a whole and the causes and speed of these changes, which in turn will provide the possibility of predicting changes, their regulation, for example, reducing the number of agricultural pests.

Density measurement is also used in cases where it is more important to know not the total population size at one time or another, but its dynamics, that is, the course of changes in population over time. The population size is all the individuals in the population.

Population index. A measure of abundance can also be indicators related not to a unit of space, but to a unit of time, for example, the number of birds noted during an hour, or the number of fish caught per day. In fact, these indicators differ from density only in dimension. Both are relative indicators and are called population indices.

Population densities of different representatives of mammals can differ by tens of thousands of times. However, in animals consuming a similar type of food, the differences in densities are much smaller. The more remote the population from the primary source of organic food, the lower its density. That. population density is the number of individuals per unit area.

Ecological fertility gives an idea of ​​the rate of population growth, that is, the activity of population reproduction under actual living conditions. In general, species that do not care for offspring are characterized by high potential and low ecological fertility. So, for example, an adult female cod spawns millions of eggs, of which, on average, only 2 individuals survive to adulthood.

Mortality. If we trace the fate of a certain group of individuals born at the same time, it is easy to find that their number continuously decreases during life as a result of the death of some of the individuals. The rate of the process of population decline is characterized by an indicator called mortality. Mortality characterizes the processes of population decline in individual population subgroups (for example, only among males or only among females) or in the population as a whole.

The mortality of organisms is manifested even when the living conditions are quite favorable. In these cases, we speak of minimal mortality. Its nature is associated with defects in physiological development, leading to the death of individual organisms. Under specific environmental conditions, mortality, as a rule, is above the minimum level, since the influence of external factors (predation, lack of sufficient food, environmental pollution, and others) create additional causes of death of organisms.

To a certain extent, the death rate is opposite to the birth rate. However, mortality, like fertility, is expressed in terms of the number of individuals who died over a given period of time, but more often in the form of a relative (or specific) value. The specific indicator of mortality is the percentage of individuals that died in a single period of time, or their share of the initial size of the group. In most organisms, the rate of mortality varies throughout life. It is usually high early stages its development, then decreases and increases again in old age.

The age structure of a population characterizes the total number of age groups represented in it and the ratio of their numbers or the total mass of organisms present in the group (biomass). This ratio is usually called the age distribution (that is, the distribution of numbers by age groups) or the age spectrum of the population. The age structure of a population can change under the influence of external factors, since they control the processes of both fertility and mortality.

The analysis of the age structure of populations and the allocation of age groups in plants and animals is carried out in different ways. The ability of the population to self-maintenance of numbers and its resistance to external influences are assessed by the age spectrum. The more complex the age spectrum, the more stable the reproduction of the population. An analysis of the age structure makes it possible to predict the population size for the next few years, which is used, for example, to assess the possibilities of catching fish in a hunting economy, in some zoological studies.

The peculiarities of the age structure determine many properties of a population as a system. A population that includes many age groups is less affected by the factors that determine breeding success. After all, even extremely unfavorable conditions of reproduction, capable of leading to the complete death of the offspring of a given year, are not catastrophic for a population of a complex structure.

The life of a population is manifested in its dynamics. A population cannot exist without constant changes, due to which it, as it were, adapts to changes in external conditions.

In the course of evolution, different types of living organisms acquire different properties. Some of them are adapted to exist in harsh but stable conditions, for example, in deserts, semi-deserts, and tundras. An example is plants such as saxaul and tamarisk that live in desert zones, or some types of mosses that inhabit the tundra.

The species properties of organisms living in such conditions are also reflected in the properties of their populations. The processes of maintaining the abundance and structure of the populations of these species (reproduction processes) become highly sensitive to violations of environmental conditions. They become easily vulnerable to increasing human impact and are difficult to restore.

Other species found in the zones temperate climate, especially populations of annual animals (most insects) and plants (some types of grasses), are able to withstand significant disruption to living conditions. Fluctuations in their numbers are characterized by a wide range. During the years of minimum and maximum abundance, the number of such populations can differ by tens, hundreds, and sometimes thousands of times.

Population growth. At first glance, it is clear that the nature of the dynamics of the abundance of various species of organisms in a population should be associated with demographic indicators, which are also formed in the process of evolution and reflect the living conditions of a species in a particular habitat. Nevertheless, despite the fact that both fertility and mortality, and the age structure are very important, none of these indicators can be used to judge the properties of the dynamics of the population as a whole.

To a certain extent, these properties are revealed by the process of population growth, which characterizes its ability to restore numbers after a catastrophe or to increase numbers when organisms populate free ecological niches.

Population fluctuations. When the growth of the population is completed, its numbers begin to fluctuate (compared to a more or less constant value). This phenomenon is caused by various factors. The process of population dynamics itself can also manifest itself in different ways.

In many species of animals and plants, population fluctuations are caused by seasonal changes in living conditions (temperature, humidity, light, food supply, etc.). Examples of seasonal fluctuations in the number of populations are demonstrated - clouds of mosquitoes, forests full of birds, fields overgrown with cornflowers - in the warm season, in winter period these phenomena are practically eliminated.

Of greatest interest are the fluctuations in the number of populations that occur from year to year. They are called interannual as opposed to intra-annual, or seasonal. Interannual population dynamics may have different character and manifest itself in the form of smooth waves of changes (abundance, biomass, population structure) or in the form of frequent abrupt changes.

In both cases, these changes can be regular, that is, cyclic, or irregular - chaotic. The former, unlike the latter, contain elements that repeat at regular intervals (for example, every 10 years the population reaches a certain maximum value).

The fluctuations in the number of some species of birds (for example, the city sparrow) or fish (bleak, vendace, gobies, etc.) observed from year to year give an example of irregular changes in the size of the population, usually associated with changes in climatic conditions or changes in environmental pollution living with substances that have a detrimental effect on organisms.

The most well-known examples of cyclical fluctuations include joint fluctuations in the abundance of some species of northern mammals. For example, cycles of three- and four-year periodicity are characteristic of many northern murine rodents (mice, voles, lemmings) and their predators (polar owl, arctic fox), as well as hares and lynxes.

In Europe, lemmings sometimes reach such high densities that they begin to migrate out of their overcrowded habitats. In both lemmings and locusts, not every case of an increase in numbers is accompanied by migration.

Sometimes cyclic fluctuations in population size can be explained by complex interactions between populations of different animal and plant species in communities.

As an example, let us consider fluctuations in the number of certain insect species in European forests, for example, butterflies of the pine moth and larch leafworm (Fig. 24), the larvae of which feed on the leaves of trees. The peaks of their numbers are repeated in about 4-10 years.

Fluctuations in the abundance of these species are determined both by the dynamics of tree biomass and fluctuations in the abundance of insect-eating birds. As the biomass of trees in the forest increases, the largest and oldest trees become susceptible to budworm caterpillars and often die from repeated defoliation (loss of leaves).

Dying and decomposition of wood returns to the forest soil nutrients. They are used for their development by young trees that are less sensitive to attack by insects. The growth of young trees is also facilitated by an increase in illumination due to the death of old trees with large crowns. In the meantime, the birds are reducing the number of budworms. However, as a result of the growth of trees, it (number) again begins to increase and the process repeats.

If we consider the existence of coniferous forests over long periods of time, it becomes clear that the leaf roller periodically rejuvenates the ecosystem of the coniferous forest, and is an integral part of it. Therefore, the increase in the number of this butterfly does not represent a catastrophe, as it may seem to anyone who sees dead and dying trees at a certain stage of the cycle.

The reasons for sharp fluctuations in the number of some populations can be various abiotic and biotic factors. Sometimes these fluctuations are in good agreement with changes in climatic conditions. However, in some cases, it is impossible to explain changes in the size of a particular population by the influence of external factors. The causes that cause population fluctuations may lie in themselves; then one speaks of internal factors of population dynamics.

population regulation. Population regulation is understood as the ability of a population to self-repair the number of its individuals to its usual size, determined by the conditions and resources of its population. ecological niche. This ability is provided by a system of mechanisms that, as it were, automatically work when the population density reaches either too high or too low values. Regulatory mechanisms can have the character of behavioral, demographic, physiological reactions of organisms to changes in their density.

Cases are known when, under conditions of overpopulation, a number of mammals undergo sharp changes in their physiological state. Such changes primarily affect the organs of the neuroendocrine system, affecting the behavior of animals, changing their resistance to diseases and other types of stress. Sometimes this leads to increased mortality of individuals, and then to a decrease in population density. White hares, for example, during periods of peak numbers often die suddenly from “shock sickness”. In some fish species, with a high abundance of individuals, adults switch to feeding on their juveniles, as a result of which the population begins to decline.

One should not think that the presence of regulatory mechanisms should always stabilize the population. In some cases, their action can lead to cyclic fluctuations in numbers even under constant living conditions. Traces of the manifestation of various actions of regulatory factors are quite often found in the dynamics of populations, which are characterized by cyclic fluctuations in numbers.

Species populations are the main functional units of wildlife. They are elements of communities, ecosystems, participating in the main processes of matter transformation and energy transfer.

Populations have characteristic indicators that are unique to them, such as structure, density, abundance, birth rate, and mortality. Some characteristics of populations are interrelated: mortality determines the structure, fertility - density, etc.

The processes of changes in populations over time are called population dynamics. These changes are the result of the action of many environmental factors, as well as internal mechanisms of population regulation.

The number, density, sex and age composition of the population change all the time. These changes are associated both with external causes in relation to the population, and with internal mechanisms of regulation inherent in each population. All these changes are important for the population, helping it survive and adapt to changing living conditions. The ratio of internal and external regulators is different. The importance of some in comparison with others is still disputed by various scientists.

Based on the information currently available in the environmental literature about the population, answer the questions and explain your answers with specific examples.

But first, find out what is Environmental challenge (situation)?

- this is a situation that has arisen in natural conditions or artificially formulated in which it is required to obtain a certain useful result in harmonizing relationships in the systems "man - environment", "nature - society", "organism - environment".

Similar information.

1. What is a population?

Answer. A population is a structural unit of a species, a set of individuals of the same species that have a common gene pool and occupy a certain territory.

The population of any kind is distributed unevenly in space, in groups. For example, stinging nettle is found within its range only in moist, shady places with fertile soils. Cabbage whites can be found where cabbage is grown - in vegetable gardens and fields. The settlements of the European mole, which we notice on the mounds of the earth (molehills), are found on forest edges and meadows.

Habitats suitable for the life of individuals of the species do not cover the entire range, therefore, it makes no sense to look, for example, for a mole in the swamp, and cabbage whites in the forest.

Groups of individuals of the same species can be large or small, exist for a long time (over the life of hundreds of generations or more) or not for long - only during the life of two or three generations. As a result of the spring flooding of rivers, temporary reservoirs are formed, in which frog eggs can be laid, as well as dragonfly and mosquito larvae. But these small groups of animals are doomed to death if under the rays summer sun the pond will dry up.

Much more important for evolution is the fate of a group of individuals, which is stably preserved for many generations. For example, the population of a large lake, either increasing or decreasing in number, can exist for quite a long time. Such groups of individuals of the same species, existing for a long time in a certain part of its range, are called populations (from the French population - the population of a territory).

The population is a supraorganismal system. In the process of cohabitation between individuals in a population, regular connections are formed. This is especially evident in animal populations. At the same time, many connections are aimed at the reproduction of the population: individuals of different sexes find each other by smell, sounds, enter into marriage relationships, build shelters, feed their young, and take care of their offspring.

Original ways of caring for offspring are known in some amphibians. The male midwife toad wraps eggs on its hind legs and sits with it for about two weeks in an earthen hole; then it moves to the nearest body of water to get rid of the eggs. The female pipa toad bears eggs on her back, in special depressions on the skin. Javanese copepod frogs, living on trees and shrubs, during spawning, together with eggs, secrete a slimy liquid, which they beat with their feet into a thick foam; after spawning, the female forms an ovoid lump from the mucous mass with her feet, to which she tightly presses the leaves located nearby. Juveniles leave the nest already in the form of small frogs.

2. Can a species consist of one population?

Answer. They can and do exist. But without human protection, such species are doomed. For example, blue fox, Iranian fallow deer or Californian condor. This rare species subject to international protection.

3. What is the role of populations in evolution?

Answer. The role of populations is great, since almost all mutations occur within it. These mutations are primarily associated with the isolation of populations and the gene pool, which differs due to their isolation from each other. The material for evolution is mutational variation, which begins in a population and ends with the formation of a species.

Question after § 79

1. Perch, ruff, crucian carp, pike, roach live in the same lake. Perch, pike, pike-perch, bream, and roach live in the adjacent water body, isolated from the first one. How many species and how many populations inhabit both reservoirs?

Answer. 10 populations 7 species

2. What are the demographic indicators of populations? How can they be used in business?

Answer. To understand the functioning of this complex system, it is very important to know not only the characteristics of the biology of certain types of organisms, but most importantly, their population characteristics, in particular, the density of settlement, the total number of individuals, the growth rate, life expectancy, the number of offspring produced. These characteristics, called population demographics, are extremely important for predicting possible changes occurring both in individual populations and in the entire community or ecosystem.

Demographic characteristics, such as fertility, mortality, age composition (structure) and number of individuals (abundance), characterize the population as a whole, reflecting the speed of the processes occurring in it. An individual organism is born, ages and dies. With regard to an individual, it is impossible to talk about fertility, mortality, age structure, abundance - characteristics that make sense only at the group level.

They are used to predict processes further development, use, recovery.

3. What is the practical significance of studying populations? Give examples.

Answer. The study of populations is important for predicting the changes occurring in them and their regulation. For example, when harvesting timber, it is very important to know the rate of forest restoration in order to correctly plan the intensity of felling. The situation is similar with animal populations that are used by humans to obtain food or fur raw materials. Practically significant from a health point of view is the study of populations of small rodents - carriers of the causative agent of a disease dangerous to humans - plague.

4. What properties of a population are determined by the characteristics of its age composition?

Answer. The age structure of a population is characterized by the ratio of the number or biomass of individuals of different ages. This ratio is called the age distribution of the population, i.e., the distribution of numbers by age groups. The age composition of the population depends on the intensity of mortality of organisms and on the magnitude of the birth rate.

Even within the same population, significant changes in age structure can occur over time. Such changes, however, automatically turn on mechanisms that return the population back to some normal age distribution characteristic of this population.

An analysis of the age structure makes it possible to predict the number of populations for a number of next generations and years, which is used, for example, to assess the possibilities of fishing, in hunting, and in some zoological studies.

5. Why are populations of different ages less sensitive to sudden short-term changes in the conditions of reproduction?

Answer. The peculiarities of the age structure determine many properties of a population as a system. A population that includes many age groups is less affected by factors that determine breeding success in a particular year. After all, even extremely unfavorable breeding conditions that can lead to the complete death of the offspring of a given year are not catastrophic for a population of complex structure, because the same parent pairs participate in reproduction many times.

At the beginning of the season, 1000 fish were tagged. In the course of subsequent fishing, 350 tagged fish were found in the total catch of 5000 fish. What was the population size before the fishery began?

Answer. The problem is solved through the proportion

1000 tagged - x (population size)

350 tagged - 5000 caught

x \u003d 1000 * 5000 / 350 \u003d 14,285.7 \u003d 14,286 fish

Answer: the number before the start of fishing is 14,286 fish

Populations and their ecological characteristics.

Within the range of a certain species, the conditions for the existence of organisms are not the same, therefore, there will be differences between the structural groups of the species. For example, a species of river perch has coastal and deep-sea populations. The number of populations depends mainly on the size of the range and the variety of living conditions. Groups of spatially adjacent populations may form a geographic race, or subspecies. The unity of the individuals of the population ensures free crossing - panmixia. Each population is characterized by certain features that emphasize its ecological features. The section of ecology that studies the conditions for the formation, structure and dynamics of the development of populations of individual species is commonly calledpopulation ecology.

Ecological characteristics of populations is a list of features that describe the interaction of populations with a complex environmental factors certain habitat.

Any population of a species occupies a certain territory, which is commonly called population range. The range of a population can have a different size, depending largely on the degree of mobility of individuals. Each population is characterized numbering -the number of individuals that is part of the population and occupies a certain area or volume in the biocenosis. Any population is theoretically capable of unlimited growth in numbers, but it is limited by the resources that are necessary for normal functioning. The number of individuals in the population fluctuates within certain limits, but it should not be below a certain limit. Reducing the number below this limit can lead to the extinction of the population. The population size is determined births, deaths, their ratio in the form of natural increase, as well as immigration (settlement) and emigration (eviction). fertility- the number of individuals in the population, is born per unit of time, and mortality- the number of individuals in the population that die during the same time. If the birth rate prevails over the death rate, then there will be positive natural increase and the population will increase. In accordance with the size of the population area and the number of individuals, the density is calculated populations. Population density is determined by the average number of individuals per unit area or volume. For each set of environmental conditions, there is a certain optimal population density determined by the capacity of the habitat. Population density can be displayed through an indicator such as biomass. Population biomass - the mass of individuals in a population per unit area or volume.

2. Population structure.

Within a population, groups can be distinguished that determine its characteristic structure..

Population structure - division of the population into groups of individuals that differ in certain properties (size, sex, location, behavioral features, etc.).

There are the following types of population structure:

1) sexual structure- the ratio of individuals of different sexes;

2) age structure- distribution of individuals in the population by age groups;

3) spatial structure- distribution of individuals of a population over the territory it occupies;

4) ethological structure- a system of relationships between individuals, which is manifested in their behavior; Thus, the main forms of organization of animal populations are a single way of life (for example, most spiders, a mallard duck) and a group way of life in the form of families (true lions), colonies (in wild rabbits, sand martins), packs (in locusts, wolves ), herds (in ungulates, cetaceans).

3. Population waves .

population waves - these are periodic or non-periodic changes in the number of populations under the influence of various factors. This concept was introduced by S.S. Chetverikov. Population waves are one of the causes of genetic drift, causes the following : growth of genetic homogeneity (homozygosity) of the population; a change in the concentration of rare alleles, the preservation of alleles that reduce the viability of individuals; change in the gene pool in different populations. All these phenomena lead to evolutionary transformations of the genetic structure of the population, and in the future to a change in the species..

Population waves are seasonal and non-seasonal:

Seasonal population waves - due to features life cycles or seasonal change of climatic factors;

off-season population waves - caused by changes in various environmental factors.

The population itself can maintain its numbers indefinitely. At the population level, there are processes of self-regulation that bring the density of the population in line with the capacity of the habitat and manifest themselves in the form of waves of life.

The main mechanisms of regulation of population size are:

1) regulation by relationships with populations of other species (for example, the number of lynx depends on the number of hares);

2) regulation by dispersal (migration of proteins);

3) regulation of social behavior (in social insects, separate female queens and males participate in reproduction, the number of which is regulated in the process of reproduction);

4) regulation of territorial behavior (territory marking in bears, bison, tigers)

5) regulation by overpopulation and stress behavior (the phenomenon of cannibalism in gulls).

As a result of long-term adaptation to the conditions of existence, populations have developed mechanisms that allow them to avoid unlimited growth in numbers and help maintain population density at a relatively constant level.

4.Population homeostasis - ϶ᴛᴏ maintaining the population size at a certain, optimal level for a given habitat. Population homeostasis is influenced by abiotic factors, as well as interspecific and intraspecific relationships. 5. Ecosystems, their structure and properties.

Ecosystem-a set of organisms of different species and their habitats, connected by the exchange of matter, energy and information. A home aquarium, a lake on the outskirts of a village, a steppe ravine, a forest area, a spacecraft cabin, our entire planet are all ecosystems of a single biosphere. The concept of "ecosystem" was proposed in 1935 by A. Tesley. The functioning of the ecosystem is ensured by the ʼʼʼʼʼʼʼ' biological circulation of substances between the abiotic and biotic parts. Ecosystems are open biosystems, and in connection with this, for existence in time, ʼʼʼʼ external flows of energy, matter and information are needed as part of the general geological cycle.

Close to ecosystems is biogeocenoses.

Biogeocenosis-it is a certain territory with homogeneous conditions of existence, inhabited by interconnected populations of different species, united among themselves by a circle of substances and a flow of energy. The concept of biogeocenosis was introduced by V.M. Sukachev (1940). The basis of the vast majority of biogeocenoses are photosynthetic organisms that form plant groups. Biogeocenosis, unlike an ecosystem, is a specific, territorial concept, because it occupies a limited area with homogeneous conditions of existence and with the corresponding phytocenosis (plant groups).

In an ecosystem, there are biotic and abiotic parts. The biotic part of an ecosystem is a collection of interconnected living organisms that form a biocenosis. Biocenosis is a grouping of interconnected populations of organisms of different species inhabiting a site with homogeneous conditions of existence. This concept was proposed by the German hydrobiologist K. Mjobius. The basis of biocenoses is phytocenosis(plant groups), with which zoocenoses (groups of animals) and microbiocenoses (groups of microorganisms) are associated. Biocenoses exist in a certain area of ​​​​the environment, which is commonly called biotope.

The biotic part of the ecosystem make up various environmental groups of organisms united by spatial and trophic relationships - producers, consumers and decomposers.

Producers - populations of autotrophic organisms capable of synthesizing organic matter from inorganic. These are green plants, cyanobacteria, photosynthetic and chemosynthetic bacteria. In aquatic ecosystems, the main producers are algae, and on land, plant seeds.

decomposers- populations of heterotrophic organisms, which in the process of life decompose dead organic matter into minerals, which are then used by producers. These are heterotrophic saprophytic organisms - bacteria and fungi that secrete enzymes and organic residues and absorb their breakdown products. Detritophages participate in the processes of decomposition of organic compounds (they consume crushed organic matter, for example, earthworms, fly larvae), saprophages eat animal and human droppings, for example, dung beetles), necrophages (eat animal corpses, for example, dung beetles).

Part abiotic part biogeocenosis includes the following components:

inorganic substances-compounds that are included in the biogenic migration of substances (for example, CO 2, O 2, nitrogen, water, hydrogen sulfide, etc.);

organic matter- compounds that connect the abiotic and biotic parts of the ecosystem;

Microclimate, or climatic regime - a set of conditions that determine the existence of organisms (illumination, temperature regime, humidity, terrain, etc.).

Main properties ecosystems are: integrity, self-reproduction, sustainability, self-regulation, etc... Relationships between populations in ecosystems . The composition and structure of groups, their stability and change depend on complex relationships between populations of different species. There are the following link types between individual populations of different species in ecosystems:

Indirect- populations of one species affect the population of another indirectly, through the populations of the third (predators, eating prey, affect plant populations);

Trophic- these are food connections (predator-prey);

topical- these are spatial connections (orchids on tree trunks);

Antibiotic Relationships(predation, competition, predation) - each of the interacting populations of different species experiences Negative influence another;

Neutral relationships- the existence of a population of different species on the common territory does not entail any consequences for each of them (predators of different species);

6. Self-regulation of ecosystems. Agrocenoses. Self-regulation– the ability to restore internal balance after any natural or anthropogenic impact. Fluctuations in quantitative and qualitative indicators characterizing ecosystems occur around certain average (optimal) values. Ecosystem stability implies constancy (homeostasis) populations of each species. Regulatory factors that smooth out fluctuations in the number of individual species are intraspecific and interspecific relationships. The equilibrium state of a population is determined by the ratio of limiting factors that predetermine the resistance of the environment, on the one hand, and the biotic potential of reproduction, on the other. The ecosystem only strives for sustainability, but never achieves it: firstly, external conditions change, and secondly, species change their habitats.

Control of knowledge and skills:

1) What is the population structure?

2) What are the types of population structure?

3) How is the population size regulated?

4) What is the main factor influencing the homeostasis of a population?

5) what is the difference between an ecosystem and a biogeocenosis?

Homework: retelling of the abstract͵ §28.29, (30-33.47) prepare messages, Lec. No. 25.

Populations and their ecological characteristics. - concept and types. Classification and features of the category "Populations and their ecological characteristics." 2017, 2018.