Presentation of a population as a form of existence of a species. Populations as a form of existence of a species

A population is a collection of individuals of the same species that exists for a long time in a certain territory (range) and is separated from other populations by one form or another of isolation. The population is the elementary structure of the species, in the form of which the species exists in nature.

The population is an elementary evolutionary structure. Under the influence of environmental factors, hereditary changes (mutations) constantly occur in the population. Since mutations are passed on to offspring, as a result of crossing they spread in the population and saturate it, the population becomes heterogeneous. As a result of the action of evolutionary factors, those individuals that have acquired hereditary changes that are useful in given environmental conditions survive and leave offspring. This is how the ecological criterion of the population and the species as a whole is formed.

The main characteristics of the population are: density, abundance, birth rate, mortality, age composition, distribution within the territory and growth rate.

Population density is determined by the number of individuals per unit area or volume. The territory occupied by different populations of the same species varies and depends on the degree of mobility of individuals. Each species has a certain population density, deviations from which in both directions adversely affect the rate of reproduction and vital activity of individuals.

The number is the total number of individuals in the allocated area. The number or number of individuals in a population is different for different species and largely depends on the stability of the ecological situation. The number cannot be below certain limits; a decrease in numbers beyond these limits can lead to the extinction of the population. In sexual reproduction, the exchange of genes turns the population into a relatively complete genetic system. If there is no cross-fertilization and vegetative reproduction predominates, the genetic links are weaker and the population is a system of clones or pure lines sharing the environment. Such populations are united mainly by ecological ties.

In all cases, populations have laws that make it possible to use even limited environmental resources to leave offspring. Populations of many species have properties that allow them to regulate their numbers.

Maintaining a population that is optimal under given conditions is called population homeostasis. The homeostatic capabilities of populations are different and they are realized through the relationship of individuals with each other and with the environment.

Birth rate is the number of new individuals that appeared as a result of reproduction per unit of time. Fertility is determined by many factors, such as the biological position of the species. Low fecundity is characteristic of those species that take great care of their offspring. The birth rate depends on the rate of puberty, the number of generations per year, and the ratio of males and females in the population. To a large extent, the birth rate in nature is determined by the availability of food, the ability to feed offspring and the influence of natural conditions.

Mortality is an indicator that reflects the number of individuals who died in a population over a certain period of time. It can be very high and varies depending on environmental conditions, age and state of the population. In most species, mortality in early age always

is higher than in adults. Mortality factors are very diverse. It can be caused by the influence of abiotic environmental factors (low and high temperatures, heavy rainfall, hail, excessive or insufficient humidity), biotic factors (lack of food, infectious diseases), anthropogenic factors (environmental pollution, destruction of animals, trees).

Population growth is the difference between births and deaths, population growth can be either positive or negative.

The population growth rate is the average population growth per unit of time.

Age composition - is essential for its existence. Under favorable conditions, the population contains all age groups and maintains a more or less stable age composition. In rapidly growing populations, young individuals predominate, while in declining populations, old ones, no longer able to reproduce intensively, predominate. Such populations are unproductive and not stable enough.

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 features reflect the structure of the population. 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 population structure thus has an adaptive character. Different populations of the same species have both similar features and distinctive features that characterize the specifics of environmental conditions in their habitats.

In general, in addition to the adaptive capabilities of individual individuals, adaptive features of the group adaptation of the population as a supra-individual system are formed in certain territories.

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population- a group of individuals species inhabiting the same territory, having a common gene pool (the totality of the genotypes of all individuals of the population.) And the ability to freely interbreed.

A population is a form of intraspecific organization or a form of existence of a species that ensures the most complete use by a given group of individuals of the natural resources of the territory to which the population is confined. The biological significance of a population consists in the most complete and rational use energy resources, allowing to ensure the abandonment of offspring. During sexual reproduction, the exchange of genes turns the population into an integral genetic system. If reproduction occurs vegetatively (shoots, buds, etc.) or other means, then the population is a system of clones, or pure lines that share the environment. In modern biology, a population is considered as an elementary unit in the process of evolution, capable of responding to changes in the environment by rearranging its gene pool.

Speaking of ecological populations, it should be noted big variety their scale. In the same species in different environments, populations can vary greatly. These differences are due to:

a) the area of ​​​​the population range - they can occupy an area comparable in area to the mainland (populations of arctic fox, mallard), and may be limited to a few square meters (some amphibians and mollusks);

b) the number of individuals that form a population - a population can unite millions of individuals (mosquitoes) or only a few dozen animals ( large predators);

c) the number of micropopulations - some populations are represented by many micropopulations confined to different biotopes, others are spatially uniform.

Thus, populations are very diverse species groups, the number and characteristics of which correspond to the diversity and conditions of the habitat, the specific properties of the environment and the biology of the animals themselves.

It is important to take into account the diversity of the interaction of organisms with the environment. In accordance with this approach, populations are distinguished:

a) according to the method of maintaining the number and time of existence:

– permanent populations that arise in optimal habitats are capable of self-reproduction and do not need an influx of individuals from outside to maintain their numbers;

– temporary populations exist not only due to internal potential, but also as a result of immigration of individuals from outside;

b) by the ability to self-reproduce:

– independent populations - able to reproduce independently; the influx of individuals in their reproduction does not play a significant role;

– semi-dependent populations - can self-reproduce, but the immigration of individuals significantly increases the number;

– dependent- mortality within the population is not compensated by the offspring, without the immigration of individuals, the population dies out;

– pseudopopulations- completely incapable of self-reproduction, entirely dependent on the influx from outside. A population of warm-water molluscs lives on Moneron Island abalone. They do not spawn in these cold waters. The population is maintained by bringing larvae from the coast of Japan with the warm Tsushima Current;

– temporary, or intermittent populations - are formed due to the eviction of individuals from permanent populations to unfavorable habitats during periods of a sharp increase in the number of permanent populations;

– hemipopulations, or semi-populations- groups of individuals belonging to individual age phases of animal development, while at different stages of their age development (ontogenesis) they have sharp differences, both morphological and ecological (adult bottom mollusks and their free-swimming pelagic larvae).

Population structures:

1. Sexual ( Figure 7.1 ) . The numerical ratio of the sexes, i.e. sex composition, and especially the proportion of breeding females in the population, has great importance for further growth. The sex ratio depends primarily on the biology of the species and varies greatly among monogamous(a male mates with one female per season) and polygamous animals. For the former (for example, cranes, swans), the norm is the sex ratio of 1:1. For the latter (for example, fur seals, baboons), the predominance of females is typical. Among monogamous animals there are almost always "reserve" males. These are already sexually mature, but not yet breeding animals; they represent the reproductive reserve of the population. The uneven death of different sexes, their unequal survival rates are common among animals. As a rule, females are more viable. AT young age females and males differ in behavior. Males are usually more mobile, less attached to shelters, therefore they more often become victims of predators and bad weather.

Under unfavorable conditions, when the population is depressed, the survival rate of females increases dramatically and the percentage of females greatly exceeds the norm. This phenomenon is of great adaptive importance, since the restoration of the undermined population depends on the females. Ecological and behavioral differences between males and females can be strongly pronounced. So, male mosquitoes feed on plant nectar and lick dew, while females are blood-sucking.

Figure 7.1 - The ratio of sexually mature males and females
different ages in the common frog population

2. Age ( Figure 7.3 ) . In long-lived and multiply reproducing species, a relatively stable population structure arises with the long existence of different generations. In species with a short period of adulthood, a significant part of the population is replaced annually. The size of such a population is unstable and can vary dramatically in individual years, and the age structure of the population varies greatly. The age composition of a population is determined by several factors, among which one can indicate the time of reaching puberty, total life expectancy, the duration of the breeding season, the life expectancy of a generation, the offspring frequency, mortality, and the type of population dynamics.

Figure 7.3 - Age structure of spruce

3. Geographic - This is a large territorial grouping of individuals of the general population of the species. It is adapted to the peculiarities of climate, topography, and the composition of the living population of different biogeocenoses in a large geographic area of ​​the species range.

4. Ecological - this is a group of individuals with the property of integrity, with a special habitat, characterized by the unity of ecological reactions to external influences. The inhabitants of one natural community a special, unique, but uniform type of reactions, a way of life of biological rhythms develops. Populations of this type are demarcated, but not isolated from each other. Therefore, quite often there is an exchange of genetic information.

5. ethological– patterns of joint behavior of animals are studied by science ethology. The forms of coexistence in a population are extremely varied.

At solitary lifestyle individuals in a population are independent and isolated from each other. However, this behavior is typical for many species only at certain stages. life cycle. They often form temporary aggregations in wintering grounds, in the period preceding fertilization.

At family lifestyle the bond between parents and offspring is strengthened. For example, in birds, care for chicks continues until they are raised on the wing; in some mammals, young are raised in family groups for several years.

The animal family is based not only on the sexual instinct and the need for joint care for offspring, but also on territorial community. A peculiar family is the lion pride. The basis of the pride are lionesses, they hunt, raise lion cubs. Usually a pride includes several lionesses and their cubs, 2-3 young males and a dominant male. He is not always the largest or the strongest, but the rest of the males recognize his dominance, and he, in turn, tolerates their presence. The pride does not protect the aged and sick lions, but expels them.

Intraspecific groupings- flocks, herds, colonies, harems. Abiotic conditions in most cases equally affect both a single individual and a group. Biotic factors have a different effect on the individual and the group of individuals.

Flocks- mobile, usually temporary associations. Accumulations of animals are often associated with places of abundance of food or fairly reliable shelters.

herds- longer and more permanent associations of animals. They include individuals of the same species that remain close to each other for some time, behave similarly, and are often characterized by the same rhythm of activity. The basis of group behavior in herds is the relationship of dominance - submission.

Colonies is a group settlement of sedentary animals. They can be long-term or occur only during the breeding season (birds - gulls, loons, etc.).

Harem- a small stable group of breeding polygamous animals (grey seal, fur seal, sperm whale).

6. Elementary - this is a small grouping of individuals of the same species in a biogeocenosis. The composition includes genetically close individuals. The difference between micropopulations is determined by the habitat.

population density is the number of individuals per unit area (Figure 7.4). The upper limit of population density is determined by the amount of the scarce resource itself. A special group of organisms are plants - annuals. The density of their populations can increase practically indefinitely. This is possible due to the fact that with an increase in density, the size of an individual decreases.

Figure 7.4 - Wolf population density

Competition leads to significant fluctuations in density. Population density is not constant and fluctuates from year to year because the amount of the most scarce resource in individual years is not constant.

An outbreak of prey population density causes an outbreak of predator population density because prey predators have enough to eat. Therefore, they do not die due to lack of food. And most populations survive. After all, the higher the level of a scarce resource, the higher the population density, i.e. how more casualties the more predators. Population density depends on the amount of food, i.e. if a lot of cones, mushrooms and acorns, etc. grow in the forest, then the squirrel population will increase.

Reasons that violate the stability of the population

Excessive mining. Each population is controlled "from above" and "from below". “From below” it is controlled by the amount of resources, and “from above” by organisms of the next trophic level. If a certain part of the biological production of a population is withdrawn by a person, then it compensates for the losses due to more intensive breeding. MRL (maximum allowable yield). Example: the rate of shooting elk is 15%, and wild boar is 30%. However, often a person exceeds this norm and tries to get "super profit" from the population. This can weaken the population.

Habitat destruction . Grazing compacts the soil and impoverishes the species composition of meadows and steppes. In the European part of Russia, feather grass populations (beautiful, Lessinga, common - pinnate) have become rare in the composition of steppe grass stands. Many insect populations have disappeared as a result of the plowing of the steppes and the development of virgin lands. Habitats of populations are destroyed by tourists and vacationers, and the suburban area by citizens. Aquatic habitats are destroyed by high-speed transport. The wave that occurs during its passage destroys juvenile fish. Fish are also dying from collisions with motor boats. To preserve populations, it is necessary to preserve at least some of the habitats where they can normally reproduce and restore density.

The reasons for the widespread decline in the number of gray goose (Weekeys) are not entirely clear. Probably, first of all, this is the destruction and change of habitats. the impact of the disturbance factor and the pressure of hunting on wintering grounds and in places of migration. Studies have shown that at nesting sites, in hard-to-reach tundra regions, the Lesser Whitefronted Goose is less at risk of death than on migration routes and on wintering grounds, where there is a shortage of habitats suitable for these geese, and the hunting pressure is much higher.

Introduction of new species . Man deliberately introduces species into various regions of the world. These species can crowd out native species, destroying their populations.

Environmental pollution. Populations of many plant and animal species are reduced in density and even disappear under the influence of agricultural and industrial pollution. The inhabitants of aquatic ecosystems suffer the most from this.

Sections: Biology

Class: 10

Target: Introduce students to the concept of population. Consider the population as a form of existence of the species, as a component of biogeocenosis, as a genetic system. Discuss population types.

Tasks:

• Educational: familiarization with the concept of population. Consideration of populations from the point of view of the form of existence of a species, a component of biogeocenosis, a genetic system.
• Developing: developing skills in working with a PC, logical thinking, the ability to generalize material and draw conclusions.

During the classes

1. Learning a new topic

The topic of today's lesson: “Population as a form of existence of a species and as a special genetic system. A population is a structural unit of a species ”(slide presentation is used)

Today you must learn:

• What is a population
• Population as a form of existence of a species
• Population as a component of biogeocenosis
• Population as a genetic system
• Population types.

Work with the textbook on terminology. The term population comes from the Latin word " populus- "people", "population".

Thus, the people in the population are individuals - a set of individuals. An individual is a separate organism (a living being, an individual: lat. individuum - indivisible).

Individuals in a population differ in sex (male, female), age (rudiments, newborns, young, adults and old), in interaction with the environment.

Such a combination of interacting individuals makes it possible to consider a population as a special living system with properties of a supraorganismal character.

For life together Of great importance is the complex of devices that provides contact between them or, conversely, prevents collisions.

The individuals that make up the population continuously exchange information (hereditary, biochemical, activity, signal) - it forms the integrity of the population as a biosystem in space and time.

The population has a certain structure. The spatial structure - individual territories or plots - is characteristic of virtually all species. Density - the density of individuals in the occupied territory (slide).

Conclusion: (students do)

Each type of population may differ from each other

• by the size of the occupied territory within the species range,
• resource development
• in terms of genetic similarity.

The diversity of populations in the same species makes it possible to emphasize the adaptive capabilities of the properties of a given species, to characterize its structure, connections and relationships, and its role in nature.

Thus, populations manifest themselves as a form of existence of a species in the biosphere.

• How do populations interact?

Any species consists of smaller populations, because. uniformly distributed in space. Within the total territory occupied by the species - area - there are places both more suitable and less suitable for life. Therefore, there is some limitation populations from another. Neighboring populations communicate with each other in the processes of dispersal, transfer of seeds and primordia, and seasonal migrations. In some species, such a connection between neighboring populations is permanent, in others it is episodic. (Cm. presentation link populations)

Each population is adapted to its own conditions. As with organisms, it is impossible to find completely identical ones among populations.

Populations do not live in isolation. They interact with populations of other species, forming biotic communities - integral systems of an even higher level of organization.

• How can individuals in a group interact?
  See electr. textbook
• Number, density and structure of populations

Are populations constant?

See electr. textbook

The main characteristic of any population is its number .

The next indicator is population density. The ratio of individuals of different sexes or different ages - indicators population structure

Structure is the ratio of parts in any system. The population can be compared both by the distribution of individuals in space and by other indicators.

Give examples of population regulation in nature. In mobile animals, some individuals can move out (emigrate) outside the occupied territory and look for new habitats.

See demo

Gallery. Demonstration. General biology. Chapter 2

Silkworm

Locust. Video gallery. Population dynamics of Orthoptera.

The main processes occurring in the population.

See electronic textbook

Ecological task.

Factors affecting population size:

2. Population as a component of biogeocenosis

It is populations as parts of species, and not species as a whole, that are part of biogeocenoses. Populations of one species can be part of several biogeocenoses, which ensures the ability of the species to exist in different conditions habitat within its range.

Being part of the biogeocenosis, the population performs a certain function in it:

• serves as an energy supplier
• consumes energy on its own

Accordingly, the population occupies a certain place in the community, actively participating in the circulation of substances and the flow of energy, and occupies one or another ecological niche in the biogeocenosis (slide).

3. Population as a genetic system.

The totality of all hereditary inclinations in an individual is a genotype, and the totality of all genotypes of individuals that make up a population is called the gene pool. The gene pool characterizes the genetic system of a population.

Populations living in different geographic and ecological conditions are subject to unequal influences of abiotic and biotic environmental factors. The differences are especially pronounced in species with wide ranges. The more isolated a population is from others, the more specific it is in terms of its genetic characteristics.

Conclusions (to be done by students) Thus, populations are intraspecific groupings of individuals related by origin (kinship), for a long time co-occupying a certain space. The gene pool of a population characterizes its genetic integrity and differences from other populations of a species.

A population is an elementary evolutionary structure where elementary evolutionary phenomena take place.

4. Population - a structural unit of the species

A well-known domestic ecologist, Professor of Moscow University, Nikolai Pavlovich Naumov, in 1955 identified 3 types of populations in a heterogeneous species population:

• Geographic is a large territorial grouping of individuals of the general population of a species. Usually separated from each other by some physical barriers (seas, rivers, mountains, cities, highways, etc.). usually break up into groups confined to specific biogeocenoses or places with existing differences in the microclimate, hydrological regime, and relief. For example, some are distributed in the depths of the forest, while others are on the edge or arable land, along streams, etc.
• Ecological - this is a group of individuals with the property of integrity, inhabiting a special type of habitat in a biogeocenosis. For example, in the common vole, within a single geographical population, such ecological populations as arable and shrub-forest populations differ significantly. The first inhabits open treeless areas, meadows, arable lands, fields of cereal crops. The second settles in more closed places - among shrubs, in copses, on the edges and forest clearings.
• Elementary is a small grouping of individuals of a species in a biogeocenosis. It usually consists of genetically homogeneous (closely related) individuals. (slide)

2. Fixing. Knowledge control

• Test check (orally all)
• USE (individual cards)

3. Summing up

Conclusion: population is a structural unit of species and evolution.

Remember from the textbook "Plants. bacteria. Mushrooms and lichens”, which environmental conditions affect organisms. Give examples of such influence known to you. What is its meaning?

Species of organisms exist in nature in the form of separate populations. Each of them is characterized by certain indicators, and also has a well-defined structure of its constituent individuals.

The main indicators of the population. Number - the total number of individuals in a given area. The population is capable of self-regulation of its numbers. The maximum possible population size is determined by the resources of the environment - food, breeding grounds, shelters, etc.

Fertility - the number of new individuals that appeared in the population per unit of time and as a result of reproduction. The birth rate is determined by the ratio of sexes, age groups in the population, as well as the frequency of reproduction and the fecundity of individual individuals.

Mortality - the number of individuals who died in a population in a certain unit of time. Mortality depends on weather and climatic conditions, the actions of predators, the influence of diseases and other adverse environmental conditions.

Population growth is the difference between births and deaths. It can be positive (the population is increasing) or negative (the population is decreasing). For example, aphids living on the green shoots of various plants can give 15 generations in one summer, which increases the number of their populations hundreds of times (Fig. 137). With the onset of cold weather, the number of aphids in the population decreases sharply, since adult insects die, and only laying of their eggs hibernate.

Rice. 137. Population of aphids on plant shoots

Structural organization of the population. In each population there are individuals that differ in sex and age. This determines their gender and age structure.

Sexual structure - the ratio of individuals in a population by sex. In most populations, it corresponds to 1:1 at the time of birth. However, as a result of the death of individuals of either sex, this proportion may change. For example, in a population of mallard ducks, after wintering, the number of females decreases by 20%.

Age structure - the ratio of individuals in a population by age. The presence of individuals of different ages in a population increases its adaptive capabilities. The ratio of age groups in a population determines its ability to increase or decrease in numbers. Thus, an increase in the number of young individuals in the Asian locust population due to warm winter leads to a rapid increase in the number and the need to use plant protection products against this dangerous pest(Fig. 138).

Rice. 138. The Asiatic locust population in spring consists mainly of young individuals

Behavioral structure - a system of relationships between individuals in a population. This structure is typical only for animal populations. With a solitary lifestyle, the individuals of the population are isolated and independent of each other (Fig. 139). However, animals cannot constantly lead a solitary existence, since in this case the meeting of males with females and reproduction is difficult.

Rice. 139. Fox - an animal leading a solitary lifestyle

Some animals, such as wolves, unite to live together in packs (Fig. 140). In flocks, imitative reactions are highly developed and there is a strict order. All actions of the pack members are coordinated by sound, visual or chemical alarms. During the breeding season, the flock usually breaks up into separate pairs that give birth and raise offspring.

Rice. 140. A pack of wolves can handle a fairly large prey

In families, bonds and relationships between parents and offspring are strengthened. For example, this way of life is typical for African lions. A lion family (pride) consists of an adult male, several females and their cubs. Adult members of the pride hunt together, protect and raise offspring (Fig. 141).

Rice. 141. Pride of lions on the hunt

Longer and more permanent than a flock and a family, the association of animals is called a herd. In herds, there is usually a leader, which becomes the most powerful individual. The leader takes charge of all the activities of the herd and maintains a strict hierarchy of its members through special signals, threats or direct attacks. In such herds, all individuals have a certain rank - from the highest to the lowest, which determines, for example, the preferential right to consume food, approach a watering hole and provide protection from enemies (Fig. 142).

Rns. 142. When threatened, a herd of musk oxen forms a protective ring of strong males around weaker females with cubs.

population regulation. Population growth is being held back various conditions environment: weather and climate, lack of food, predators, the influence of diseases, etc. Thus, in rainy summers, the number of insects is noticeably reduced, which leads to the death of a significant number of nestlings in insectivorous birds. harsh winter with high snow cover is the cause of death of ungulate mammals, such as deer, feeding on the ground.

Rice. 143. Pine cocoon

Most often, the population size from year to year fluctuates around the average level. At the same time, in years favorable for the life of the population, its number can increase sharply. There is a so-called outbreak of reproduction. And then the environmental conditions begin to act, returning the population size to the initial average level.

Rice. 144. Graph of the regulation of the number of pine cocoon moths in the Siberian taiga

The multiplicity of mechanisms for regulating the size of a population leads to the fact that its catastrophic growth rarely occurs in nature, the undermining of environmental resources and the death of the population.

Lesson learned exercises

1. What do numbers, births, deaths and population growth show?
2. Describe the sex, age and behavioral structure of populations in nature.
3. What is the advantage of family, herd and herd ways of life in comparison with solitary? Give examples of animals leading solitary, family, pack and herd lifestyles.
4. How is the regulation of the population in nature?
5. Why in nature is extremely rare the death of a population of one or another type of organism? What prevents this?