What is the ability of the population. Disturbances in the equilibrium state of populations: mutations, natural selection, migrations, isolation

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Biology Lesson Plan

Topic: Genetic composition of populations

genetics mutational hereditary population

Type of lesson: a lesson that reveals the content of the topic.

The purpose of the lesson: continue to deepen and expand knowledge about populations, to characterize the concept of the gene pool of populations.

Tasks:

Educational. To form the concept of population genetics; characterize the gene pool of a population; find out that the mutation process is a constant source of hereditary variability.

Developing. Continue to form the ability to observe and note the main thing when listening to messages, working with textbook material.

Educational. Continue to form a scientific outlook, love for nature, work culture based on keeping records in a notebook.

Equipment

Tables, textbook.

During the classes

1. Organizational moment 1-2 min. Interview homework: 1) What is a population? 2) Why do biological species exist in the form of populations? 5-7 min.

2. Learning new material. 25 min.

3. Consolidation of the studied material. Grading.

4. Homework.

2. Learning new material

Consolidation of the studied material

4. Homework

population genetics. At the time of Darwin, the science of genetics did not yet exist. It began to develop at the beginning of the 20th century. It became known that the carriers of hereditary variability are genes.

Representations of genetics have introduced additional in-depth explanations into the theory of natural selection by Charles Darwin. The synthesis of genetics and classical Darwinism led to the birth of a special area of research - population genetics, which made it possible to explain from new positions the processes of changing the genetic composition of populations, the emergence of new properties of organisms and their consolidation under the influence of natural selection.

Gene pool. Each population is characterized by a certain gene pool, i.e. the total amount of genetic material that is made up of the genotypes of individual individuals.

The necessary prerequisites for the evolutionary process are the occurrence of elementary changes in the apparatus of heredity - mutations, their distribution and fixation in the gene pools of populations of organisms. Directed changes in the gene pools of populations under the influence of various factors are elementary evolutionary changes.

As already noted, natural populations in different parts The ranges of the species are usually more or less distinct. Within each population there is free interbreeding of individuals. As a result, each population is characterized by its own gene pool with ratios of various alleles inherent only to this population.

The mutation process is a constant source of hereditary variability. In a population consisting of several million individuals, several mutations of literally every gene present in this population can occur in each generation. Due to combinative variability, mutations spread in a population.

Natural populations are saturated with a wide variety of mutations. This was noticed by the Russian scientist Sergey Sergeevich Chetverikov (1880-1959), who found that a significant part of the variability of the gene pool is hidden from view, since the vast majority of the resulting mutations are recessive and do not appear outwardly. Recessive mutations seem to be “absorbed by a species in a heterozygous state”, because most organisms are heterozygous for many genes. Such latent variability can be revealed in experiments with crossing closely related individuals. With such a cross, some recessive alleles that were in a heterozygous and therefore latent state will go into a homozygous state and will be able to appear.

Significant genetic variability of natural populations is easily detected in the course of artificial selection. In artificial selection, those individuals are selected from the population in which any economically valuable traits are most pronounced, and these individuals are crossed with each other. Artificial selection is effective in almost all cases when it is resorted to. Therefore, in populations there is genetic variability for literally every trait. given organism.

The forces that cause gene mutations operate randomly. The probability of a mutant individual appearing in an environment in which selection will favor it is no greater than in an environment in which it will almost certainly perish. S.S. Chetverikov showed that, with rare exceptions, most of the newly emerging mutations are harmful and in the homozygous state, as a rule, reduce the viability of individuals. They persist in populations only through selection in favor of heterozygotes. However, mutations that are detrimental in some conditions may increase viability in other conditions. Thus, a mutation that causes the underdevelopment or complete absence of wings in insects is certainly harmful in normal conditions, and wingless individuals are quickly replaced by normal ones. But on oceanic islands and mountain passes, where strong winds blow, such insects have advantages over individuals with normally developed wings.

Since any population is usually well adapted to its environment, major changes usually reduce this fitness, just as large accidental changes in the mechanism of a clock (removal of some spring or addition of a wheel) lead to its failure. There are large stocks of such alleles in populations that do not bring it any benefit at a given place or at a given time; they remain in the population in a heterozygous state until, as a result of a change in environmental conditions, they suddenly turn out to be useful. As soon as this happens, their frequency under the influence of selection begins to increase, and eventually they become the main genetic material. This is where the population's ability to adapt lies, i.e. adapt to new factors - climate change, the emergence of a new predator or competitor, and even human pollution.

An example of such adaptation is the evolution of insecticide-resistant insect species. Events in all cases develop in the same way: when a new insecticide (a poison that acts on insects) is introduced into practice, a small amount of it is enough to successfully control an insect pest. Over time, the concentration of the insecticide has to be increased until, finally, it is ineffective. The first report of insecticide resistance in insects appeared in 1947 and related to housefly resistance to DDT. Subsequently, resistance to one or more insecticides has been found in at least 225 species of insects and other arthropods. Genes capable of conferring insecticide resistance appear to have been present in each of the populations of these species; their action and ensured the ultimate reduction in the effectiveness of poisons used for pest control.

Thus, the mutation process creates material for evolutionary transformations, forming a reserve of hereditary variability in the gene pool of each population and species as a whole. By maintaining a high degree of genetic diversity in populations, it provides the basis for the operation of natural selection and microevolution.

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1. What is natural selection?

Answer. Natural selection is a process originally defined by Charles Darwin as leading to the survival and preferential reproduction of individuals who are more adapted to given environmental conditions and have useful hereditary traits. In accordance with Darwin's theory and the modern synthetic theory of evolution, the main material for natural selection is random hereditary changes - recombination of genotypes, mutations and their combinations.

2. What is a genotype?

Answer. The term "genotype" was introduced into science by Ioganson in 1909. Genotype (genotype, from the Greek genos - genus and typos - imprint, shape, pattern) - the totality of the body's genes, in a broader sense - the totality of all hereditary factors of the body, as nuclear , and non-nuclear. The combination of unique genomes (sets) obtained from each of the parents creates the genotype that underlies the genetic personality. The concepts of genotype and phenotype are very important in biology. As mentioned above, the totality of all the genes of an organism makes up its genotype. The totality of all signs of an organism (morphological, anatomical, functional, etc.) is the phenotype. Throughout the life of an organism, its phenotype can change, but the genotype remains unchanged. This is due to the fact that the phenotype is formed under the influence of the genotype and environmental conditions. The word genotype has two meanings. In a broad sense, it is the totality of all the genes of a given organism. But in relation to experiments of the type that Mendel set up, the word genotype denotes a combination of alleles that control a given trait (for example, organisms can have the genotype AA, Aa or aa).

Thus, the genotype is: - the totality of genetic (genomic) characteristics characteristic of a given individual and the characteristics of certain pairs of alleles that the individual has in the region of the genome under study.

Questions after § 55

1. What is the gene pool of a population?

Answer. Each population is characterized by a certain gene pool, that is, the total amount of genetic material that is made up of the genotypes of individual individuals.

As already noted, natural populations in different parts of the range of a species are usually more or less different. Within each population there is free interbreeding of individuals. As a result, each population is characterized by its own gene pool with ratios of various alleles inherent only to this population.

2. Why most of mutations are not shown outwardly?

Answer. Natural populations are saturated with a wide variety of mutations. This was noticed by the Russian scientist Sergey Sergeevich Chetverikov (1880–1959), who found that a significant part of the variability of the gene pool is hidden from view, since the vast majority of the resulting mutations are recessive and do not appear outwardly. Recessive mutations seem to be “absorbed by a species in a heterozygous state”, because most organisms are heterozygous for many genes. Such latent variability can be revealed in experiments with crossing closely related individuals. With such a cross, some recessive alleles that were in a heterozygous and therefore latent state will go into a homozygous state and will be able to appear. Significant genetic variability of natural populations is easily detected in the course of artificial selection. In artificial selection, those individuals are selected from the population in which any economically valuable traits are most pronounced, and these individuals are crossed with each other. Artificial selection is effective in almost all cases where it is resorted to. Consequently, in populations there is genetic variability for literally every trait of a given organism.

3. What is the ability of a population to adapt (adapt) to new conditions?

Answer. Since any population is usually well adapted to its environment, major changes usually reduce this fitness, just as large accidental changes in the mechanism of a clock (removal of some spring or addition of a wheel) lead to its failure. There are large stocks of such alleles in populations that do not bring it any benefit at a given place or at a given time; they remain in the population in a heterozygous state until, as a result of a change in environmental conditions, they suddenly turn out to be useful. As soon as this happens, their frequency under the influence of selection begins to increase, and eventually they become the main genetic material. This is where the ability of a population to adapt lies, i.e., to adapt to new factors - climate change, the emergence of a new predator or competitor, and even to human pollution.

An example of such adaptation is the evolution of insecticide-resistant insect species. Events in all cases develop in the same way: when a new insecticide (a poison that acts on insects) is introduced into practice, a small amount of it is enough to successfully control an insect pest. Over time, the concentration of the insecticide has to be increased until, finally, it is ineffective. The first report of insecticide resistance in insects appeared in 1947 and related to housefly resistance to DDT. Subsequently, resistance to one or more insecticides has been found in at least 225 species of insects and other arthropods. Genes capable of conferring insecticide resistance appear to have been present in each of the populations of these species; their action and ultimately ensured a decrease in the effectiveness of poisons used for pest control

4. How can recessive alleles be identified?

Answer. Recessive allele (recessive allele, from Latin recessus - retreat) - an allele whose phenotype does not appear in heterozygotes, but manifests itself in a homozygous or hemizygous genotype for this allele. If recessive alleles are in the homozygous state, then they will appear in the phenotype. If you need to find out if they are present in the genotype of an organism with a dominant phenotype, then analyze crosses are used. To do this, the tested organism is crossed with a carrier of a recessive phenotype. If there are recessive individuals in the offspring, then the tested organism is the carrier of the recessive gene.

Current page: 15 (total book has 26 pages) [accessible reading excerpt: 18 pages]

§ 53. View, its criteria

1. What is a view?

2. What types of plants and animals do you know?

View. With the development of biology came the understanding that, compared with the infinite variety of conditions in which life takes place, the variety of forms of organisms is finite; it is, as it were, assembled into "nodes" - biological species.

Species - this is a set of individuals that have the ability to interbreed with the formation of fertile offspring; inhabiting a certain area; having a number of common morphological and physiological features and similarities in their relationship with the biotic and abiotic environment.

Biological species is not only a systematic category. This is a holistic and isolated element of wildlife from other species. The integrity of a species is manifested in the fact that its individuals can live and reproduce only by interacting with each other due to the mutual adaptations of organisms developed in the process of evolution: the peculiarities of the coordination of the structure of the maternal organism and the embryo, signaling and perception systems in animals, the common territory, the similarity of life habits and reactions to seasonal climate changes, etc. Species adaptations ensure the preservation of the species, although sometimes they can damage individual individuals. River perch, for example, feeds on their own young, due to which the species survives with a lack of food, even despite the loss of part of the offspring. Each species exists in nature as a historically emerged integral formation.

The isolation of the species is maintained by reproductive isolation (see § 59), which prevents it from mixing with other species during reproduction. Isolation is provided by differences in the structure of the genital organs, disunity of ranges, divergence in terms or places of reproduction, differences in behavior, ecological disunity, and other mechanisms that you will learn about in the following sections. The isolation of species prevents the emergence of intermediate forms. Warty birch, for example, does not grow in moss swamps, where dwarf birch usually grows. Due to isolation, the species do not mix with each other.

View criteria. Characteristic features and the properties by which some species differ from others are called criteria kind.

Morphological criterion is the similarity of external and internal structure organisms. Carl Linnaeus, for example, defined species as integral groups of organisms that differ from other life forms in terms of structure. In other words, the presence of structural features that make a certain group of organisms similar friend on a friend and at the same time different from all other groups, and there is a criterion for classifying them as a given species.

Individuals within a species are sometimes so variable that only morphological criterion it is not always possible to determine the species. There are species morphologically similar. These are twin species that are open in all systematic groups. For example, in black rats, two twin species are known - with 38 and 49 chromosomes; the malarial mosquito has 6 twin species, and the small loach fish, which is widespread in fresh water, has 3 such species. Twin species are found among the most various organisms: fish, insects, mammals, plants, however, individuals of such twin species do not interbreed (Fig. 72).

Genetic criterion is a set of chromosomes characteristic of each species; their strictly defined number, size and shape, DNA composition. The chromosome set is the main species trait. individuals different types have different sets of chromosomes, so they cannot interbreed and are reproductively restricted from each other in natural conditions.

Rice. 72. Twin species: tetraploid (left) and diploid (right) loach species

Physiological criterion - the similarity of the body's reactions to external influences, the rhythms of development and reproduction. This criterion is based on the similarity of all life processes, and above all reproduction. Representatives of different species, as a rule, do not interbreed or their offspring are sterile. However, there are exceptions. For example, dogs can produce offspring by mating with wolves. Hybrids of some species of birds (canaries, finches), as well as plants (poplars, willows) can be fruitful. Consequently, the physiological criterion is also insufficient to determine the species belonging of individuals.

Environmental criterion - this is a characteristic position for the species in natural communities, its relationship with other species, sets of factors external environment necessary for existence.

Geographic criterion - area of distribution, a certain area occupied by a species in nature.

Historical criterion - a commonality of ancestors, a single history of the emergence and development of the species.

The criteria of the species are interconnected and determine the qualitative feature of the species. But none of them is absolute. For example, two different species may not differ in anatomical structure and have the same chromosome sets. But if they differ in behavior, then they do not interbreed and, therefore, are isolated from one another. It is only in the aggregate that these criteria make it possible to establish with sufficient reliability the belonging of an organism to one species or another.

Species represent a certain level of organization of living matter - species.

biological view. Species criteria: morphological, genetic, physiological, ecological, geographical, historical.

1. Define a species.

2. What kind of criteria do you know?

3. What is the integrity of the species, how does it manifest itself?

4. Why is it important to preserve species in nature?

Make lists of plant and animal species you know. Try to group the species known to you according to the degree of similarity: a) morphological; b) ecological.

§ 54. Populations

1. Why do organisms of most of the species known to us live in groups in nature?

2. Why are groups of single-species organisms (for example, thickets of plants such as buttercup, nettle, sedge, etc.) not found everywhere, but only in certain areas? What are these areas?

In reality, a species is a much more complex formation than just a collection of interbreeding individuals similar to each other. It breaks up into smaller natural groupings of individuals - populations inhabiting separate, relatively small parts of the range of this species.

population - a group of single-species organisms occupying a certain area of the territory within the range of the species, freely interbreeding with each other and partially or completely isolated from other populations.

The existence of species in the form of populations is a consequence of the heterogeneity of external conditions.

Populations remain stable in time and space, although their numbers may change from year to year due to changes in the conditions of reproduction and development of organisms. Within populations, there are even smaller groups in which individuals with similar behavior or on the basis of family ties can unite (for example, flocks of fish or sparrows, prides of lions). However, such groups can disintegrate under the influence of external factors or mix with others. They are unable to sustain themselves.

Interrelations of organisms in populations. The organisms that make up a population are related to each other in various ways. They compete with each other for certain types of resources, they can eat each other or, on the contrary, defend themselves against a predator together. Internal relationships in populations are very complex and contradictory. The reactions of individual individuals to changes in living conditions and population reactions often do not coincide. The death of individual weakened organisms (for example, from predators) can improve the qualitative composition of the population (including the quality of the hereditary material that the population has), increase its ability to survive in changing environmental conditions.

Within each population of sexually reproducing organisms, there is a constant exchange of genetic material; interbreeding of individuals from different populations occurs much less often, so the genetic exchange between different populations is limited. As a result, each population is characterized by its own specific set of genes (gene pool - see below) with a ratio of frequencies of occurrence of different alleles inherent only to this population. Under the influence of this, properties may arise in individual populations that distinguish them from each other. Thus, existence in the form of populations increases the internal diversity of the species, its resistance to local changes in living conditions, and allows it to establish itself in new conditions. The direction and speed of evolutionary changes occurring within the species largely depend on the properties of populations. The processes of formation of new species originate in changes in the properties of individual populations.

population.

1. What is a population?

2. Why do biological species exist in the form of populations?

3. What properties of populations contribute to the sustainable existence of the species?

§ 55. Genetic composition of populations

1. What is natural selection?

2. What is a genotype?

population genetics. At the time of Darwin, the science of genetics did not yet exist. It began to develop at the beginning of the 20th century. It became known that the carriers of hereditary variability are genes. Representations of genetics have introduced additional in-depth explanations into the theory of natural selection by Charles Darwin. The synthesis of genetics and classical Darwinism led to the birth of a special area of research - population genetics, which made it possible to explain from new positions the processes of changing the genetic composition of populations, the emergence of new properties of organisms and their consolidation under the influence of natural selection.

Gene pool. Each population is characterized by a certain gene pool, i.e., the total amount of genetic material that is made up of the genotypes of individual individuals.

The necessary prerequisites for the evolutionary process are the occurrence of elementary changes in the apparatus of heredity - mutations their distribution and fixation in the gene pools of populations of organisms. Directed changes in the gene pools of populations under the influence of various factors are elementary evolutionary changes.

The mutation process is a constant source of hereditary variability. In a population consisting of several million individuals, several mutations of literally every gene present in this population can occur in each generation. Due to combinative variability, mutations spread in a population.

Natural populations are saturated with a wide variety of mutations. The Russian scientist drew attention to this Sergei Sergeevich Chetverikov(1880–1959), who found that a significant part of gene pool variability hidden from view, since the vast majority of emerging mutations are recessive and do not appear outwardly. Recessive mutations seem to be “absorbed by a species in a heterozygous state”, because most organisms are heterozygous for many genes. Such latent variability can be revealed in experiments with crossing closely related individuals. With such a cross, some recessive alleles that were in a heterozygous and therefore latent state will go into a homozygous state and will be able to appear. Significant genetic variability of natural populations is easily detected in the course of artificial selection. In artificial selection, those individuals are selected from the population in which any economically valuable traits are most pronounced, and these individuals are crossed with each other. Artificial selection is effective in almost all cases where it is resorted to. Consequently, in populations there is genetic variability for literally every trait of a given organism.

The forces that cause gene mutations operate randomly. The probability of a mutant individual appearing in an environment in which selection will favor it is no greater than in an environment in which it will almost certainly perish. S. S. Chetverikov showed that, with rare exceptions, most of the newly emerging mutations are harmful and in the homozygous state, as a rule, reduce the viability of individuals. They persist in populations only through selection in favor of heterozygotes. However, mutations that are detrimental in some conditions may increase viability in other conditions. Thus, a mutation that causes the underdevelopment or complete absence of wings in insects is certainly harmful under normal conditions, and wingless individuals are quickly replaced by normal ones. But on oceanic islands and mountain passes, where strong winds blow, such insects have advantages over individuals with normally developed wings.

Since any population is usually well adapted to its environment, major changes usually reduce this fitness, just as large accidental changes in the mechanism of a clock (removal of some spring or addition of a wheel) lead to its failure. There are large stocks of such alleles in populations that do not bring it any benefit at a given place or at a given time; they remain in the population in a heterozygous state until, as a result of a change in environmental conditions, they suddenly turn out to be useful. As soon as this happens, their frequency under the influence of selection begins to increase, and eventually they become the main genetic material. This is where the ability of a population to adapt lies, i.e., to adapt to new factors - climate change, the emergence of a new predator or competitor, and even to human pollution.

population gene pool.

1. What is the gene pool of a population?

2. Why do most mutations not show up externally?

3. What is the ability of a population to adapt (adapt) to new conditions?

4. How can recessive alleles be identified?

§ 56. Changes in the gene pool of populations

1. What is the content of the concept of "population gene pool"?

2. What is the source of changes in the gene pool?

Possessing a specific gene pool under the control of natural selection, populations play a crucial role in the evolutionary transformation of a species. All processes leading to species changes begin at the level of species populations and are directed processes of transformations of the population gene pool.

Genetic balance in populations. The frequency of occurrence of various alleles in a population is determined by the frequency of mutations, selection pressure, and sometimes by the exchange of hereditary information with other populations as a result of migrations of individuals. With relatively constant conditions and a high population size, all of these processes lead to a state of relative equilibrium. As a result, the gene pool of such populations becomes balanced; genetic balance, or the constancy of the frequencies of occurrence of different alleles.

Causes of genetic imbalance. The example given earlier with the action of insecticides suggests that the action of natural selection leads to directed changes in the gene pool of the population– increasing the frequencies of “useful” genes. Microevolutionary changes are taking place. However, changes in the gene pool can also non-directional, random character. Most often they are associated with fluctuations in the number of natural populations or with the spatial isolation of a part of the organisms of a given population.

Non-directional, random changes in the gene pool may occur due to various reasons. One of them - migration, i.e., the movement of part of the population to a new habitat. If a small part of an animal or plant population settles in a new place, the gene pool of the newly formed population will inevitably be smaller than the gene pool of the parent population. For random reasons, the allele frequencies in the new population may not coincide with those of the original. Genes, hitherto rare, can quickly spread (due to sexual reproduction) among the individuals of a new population. And previously widespread genes may be absent if they were not in the genotypes of the founders of a new settlement.

Similar changes can be observed when the population is divided into two unequal parts by natural or artificial barriers. For example, a dam was built on the river, dividing the fish population that lived there into two parts. The gene pool of a small population, originating from a small number of individuals, may, again for random reasons, differ from the gene pool of the original in composition. It will carry only those genotypes that are randomly selected among a small number of the founders of the new population. Rare alleles may be common in a new population that has emerged as a result of its isolation from the original population.

The composition of the gene pool can change due to various natural disasters, when only a few organisms survive (for example, due to floods, droughts or fires). In a population that survived a catastrophe, consisting of individuals who survived by chance, the composition of the gene pool will be formed from randomly selected genotypes. Following the decline in numbers, mass reproduction begins, the beginning of which is given by a small group. The genetic composition of this group will determine the genetic structure of the entire population during its heyday. At the same time, some mutations may completely disappear, while the concentration of others will increase dramatically. The set of genes left in living individuals may differ somewhat from that which existed in the population before the disaster.

Sharp fluctuations in populations, whatever they may be caused, change the frequency of alleles in the gene pool of populations. When unfavorable conditions are created and the population is reduced due to the death of individuals, the loss of some genes, especially rare ones, may occur. In general, the smaller the population, the higher the probability of losing rare genes, the greater the impact of random factors on the composition of the gene pool. Periodic fluctuations numbers are common to almost all organisms. These fluctuations change the frequency of genes in populations that replace each other. An example is some insects; only a small number of them survive the winter. This small fraction gives rise to a new summer population, its gene pool is often different from the gene pool of the population that existed a year ago.

Thus, the action of random factors impoverishes and changes the gene pool of a small population compared to its initial state. This phenomenon is called drift of genes. As a result of genetic drift, a viable population can develop with a kind of gene pool, largely random, since selection in this case did not play a leading role. As the number of individuals increases, the effect of natural selection will again be restored, which will be extended to the new gene pool, leading to its directed changes. The combination of all these processes can lead to the isolation of a new species.

Directed changes in the gene pool occur due to natural selection. Natural selection leads to a consistent increase in the frequencies of some genes (useful under given conditions) and to a decrease in others. As a result of natural selection, useful genes are fixed in the gene pool of populations, i.e., favorable for the survival of individuals in given environmental conditions. Their share is increasing and general composition the gene pool is changing. Changes in the gene pool under the influence of natural selection should also lead to changes in phenotypes, characteristics external structure organisms, their behavior and way of life, and ultimately to a better adaptation of the population to given environmental conditions.

genetic balance. Random changes in the composition of the gene pool. Drift of genes. Directed changes in the gene pool.

1. Under what conditions is equilibrium between different alleles of the population gene pool possible?

2. What forces caused directed changes in the gene pool?

3. What factors are the cause of genetic imbalance?

4. What are the reasons for the difference in the gene pools of isolated populations of the same species?

Discuss how human activities change the gene pool of wild and domestic animal and plant species.

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. Consequently, 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 etc. 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 common biological properties 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 capabilities of the species as a whole as a system of populations are much wider adaptive features each specific individual.

Population structure of the species

The space or area occupied by a population may be different both for different species 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 different ages representing one or different offspring of one or more 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 divided, the more possibilities to isolate 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. When weak developed abilities to movement within the species, many small populations are formed, 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 environmental factors.

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 condition into another, the ability to form clones, etc. The manifestation of all these biological features, in turn, depends on the environmental conditions. 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 pass through the next stages approximately simultaneously. 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 humans exploit natural populations of animals, taking into account their age structure has essential. 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 total strength populations, but also on the placement 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 each 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.

"Securing the site" is achieved in various ways: 1) by protecting the boundaries of the occupied space and by 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. The normal behavior of animals includes an active search for contacts with members 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 type of such a connection is the care of one of the parents about the laid eggs: guarding the clutch, 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 nervous and hormonal system affects the course of many physiological processes in the animal 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.