Definition of population main characteristics. The main environmental characteristics of the population - Hypermarket of knowledge. The concept of a population in ecology

INTRODUCTION …………………. …………………………………… .. …………… ... 3

1. Population - ecological characteristic ...................... .............. 6

2. Factors in the dynamics of population numbers .......................................... ... 9

CONCLUSION ……………………………………………. …………………… 14

LIST OF SOURCES …………………………………………………………… 17

ANNEXES

Introduction

Everything is interconnected with everything - the first environmental law says. This means that you can’t even take a step without hitting, and sometimes not violating, anything from the environment. Each step of a person on a normal lawn is dozens of destroyed microorganisms, frightened insects that change migration routes, and maybe even reduce their natural productivity.

Already in the last century, human anxiety arose over the fate of the planet, and in the current century, it came to the crisis of the global ecological system due to the increasing pressure on the natural environment.

Environmental pollution, depletion of natural resources and disruption of ecological connections in ecosystems have become global problems. And if humanity continues to follow the current path of development, then its death, according to the leading ecologists of the world, in two or three generations is inevitable.

Despite the measures taken by the Russian state to improve the environment, environmental relations continue to develop in an unfavorable direction for nature and society:

a) the departmental approach still prevails, as a result of which each environmental user exploits natural resources based on his departmental interests;

6) the so-called resource approach to environmental use is applied, as a result of which many environmental relations and natural objects that have no resource value remain outside legal protection.

The interaction of society and nature crossed the line of the previous equilibrium in the last century, and at the moment it is no longer possible to do without proper legal intervention in this area. The requirement to develop a special law on the environmental safety of Russia became urgent.

Unlike legal literature, where natural objects are studied on the basis of their economic value for society, each natural object must be studied in the totality of all its elements, which affect the life of the whole environment as a whole.

Currently, during the period of the impending environmental crisis on the whole planet, all living now need to solve the problems of the transition from exploitation and conquest of nature to its conservation and cooperation with it. Under these conditions, human ecology becomes especially important, since the normal conditions of its existence directly depend on how much a person fits into nature, is able to know its laws and use them creatively in their life.

Consuming natural resources more and more intensively with the help of vastly growing technical means, mankind in a progressive form improved the conditions for the development of its civilization and its growth as a biological species of Homo sapiens. However, by “conquering” nature, it significantly undermined the natural foundations of its own life, which created a tense and in many cases a crisis situation in the interaction of man and nature, fraught with great dangers for the future civilization. Interdependent changes have led to new relationships between the global economy and global ecology. In the past, the environmental consequences of economic growth have been disturbing. Now we cannot but be alarmed by the consequences of "environmental stress" - the deterioration in the quality of soils, water regime, the state of the atmosphere and forests - for future economic development.

It is now becoming increasingly clear that the sources and causes of pollution are much more diverse, complex and interrelated, and the effects of pollution are wider, cumulative and chronic than previously thought. The science has even formulated a definition of anthropogenic environmental pollution. This is a physico-chemical and biological change in the quality of the environment (atmospheric air, water, soil) as a result of economic or other activities that exceeds the established standards for harmful effects on the environment and poses a threat to human health, the state of the plant and animal world, and material values.

Ecology, like any science, has two aspects. One is the pursuit of knowledge for the sake of knowledge itself, and in this regard, the search for patterns of development of nature, as well as their explanation, is in the first place; the other is the application of collected knowledge to solve environmental problems. The rapid increase in the importance of ecology is explained by the fact that none of the issues of enormous practical importance cannot be solved at present without taking into account the connections between living and non-living components of nature.

The practical way out of ecology can be seen primarily in resolving environmental issues; it is she who must create the scientific basis for the exploitation of natural resources. We can state that the neglect of the laws underlying the natural processes led to a serious conflict between man and nature.

Population Environmental Characterization

A population in ecology is a group of individuals of the same species interacting with each other and co-inhabiting a common territory.

A population is a collection of individuals of one species, long existing in a certain territory, freely interbreeding and relatively isolated from other individuals of the same species.

The word "population" comes from the Latin "populus" - people, population. Thus, an ecological population can be defined as a population of one species in a certain territory.

A population possesses only its inherent features: abundance, density, and spatial distribution of individuals. Distinguish between age, sex, size structure of the population. The ratio of different age and sex groups in a population determines its main functions. The ratio of different age groups depends on two reasons: on the characteristics of the life cycle of the species and on external conditions.

Composition. Conventionally, three ecological age groups can be distinguished in a population: pre-reproductive; reproductive; post-reproductive. The duration of these ages in relation to the total life expectancy varies greatly among different organisms.

Species with a simple age structure are distinguished when the population is represented by organisms of the same age, and species with a complex age structure when all age groups are represented in the population or several generations live at the same time.

Abundance and density express the quantitative characteristics of a population as a whole. The population size is expressed by the number of individuals of a given species living on a unit of the area occupied by it. The dynamics of the population over time is determined by the ratio of fertility, mortality, and survival, which in turn are determined by living conditions.

Population density is the size of a population per unit of space: the number of individuals, or biomass, of a population per unit area or volume. Density depends on the trophic level at which the population is located. The lower the trophic level, the higher the density.

In many species, under certain conditions, mainly males or females are born, and sometimes individuals that are unable to reproduce. In aphids, for example, in summer, generations consisting of only females succeed each other. Under adverse conditions, males appear. In some gastropods, polychaete worms, fish, and crustaceans, the sex of the individual changes with age.

There are several options for determining a population. A population is a collection of individuals of the same species for a long time inhabiting a certain territory or water area, connected by one degree or another of free crossbreeding and sufficiently isolated from other similar populations. As follows from the above definition of a population, it includes the following features inherent in it:

1 Existence over a large number of generations, which distinguishes the population from short-term unstable associations of individuals.

2 The presence of a certain degree of free crossing of individuals. It is this feature of the population that ensures its unity as an evolutionary structure.

3 The degree of free crossing within the population is higher than between different (even neighboring) populations.

4 A certain degree of isolation of populations from each other.

The reasons that cause individuals of the group to group within limited areas are extremely numerous and diverse, but the main one is the uneven distribution of environmental conditions in the geographical space and the similarity of the requirements for these conditions in organisms of the same species.

Three types of populations are distinguished depending on the size of the occupied territory: elementary, ecological, and geographical (see appendix 1)

Ecological characteristics of the population.

1) number - the total number of individuals in the allocated territory;

2) population density - the average number of individuals per unit area or volume of space occupied by the population;

3) fertility - the number of new individuals that appeared per unit of time as a result of reproduction;

4) mortality - an indicator that reflects the number of deaths in a population of individuals over a certain period of time;

5) population growth - the difference between fertility and mortality; growth can be both positive and negative;

6) growth rate - the average growth per unit of time.

Similar information.

Think of the population. Population   - this is a collection of individuals of the same species with a common gene pool, crossing among themselves and for a long time inhabiting a certain space.

Depending on time and space, the habitat of species changes. It depends on many environmental factors known to you. Species not adapted to climatic conditions disappear. Their place is taken by more hardy, fit. Populations of one species exist separately from each other, as there is competition for an ecological niche. Therefore, populations of the same species occupy different territories.

Modern definitions of the population are formulated in the works of Russian researchers S. S. Schwartz, A. M. Gilyarov, A. V. Yablokov. For example, according to the definition of S. S. Schwartz (1969), a population is "elementary groups of organisms of a certain species that maintain their numbers for a long time in constantly changing environmental conditions." According to A. V. Yablokov, these are "groups of organisms of the same species that inhabit a certain territory, with a common evolutionary path of development."

Developing the ideas of his compatriots, A. M. Gilyarov gave a slightly different definition of the population.

Population   - This is a combination of organisms of the same species with a common gene pool, for a long time inhabiting a certain space and maintaining a stable reproduction of numbers. Within the population there is a constant struggle for existence, and groups of individuals of the same species are isolated from each other. They form a local, ecological, geographical population. This classification of the population was introduced by the famous Russian scientist N.P. Naumov.

A population as a biological unit has its own specific structure, property and functions. The population structure is characterized by the number of individuals and their distribution in space. And the functions of the population are identical to the functions of other biological systems. The properties characteristic of a population are growth, development, reproduction, adaptability to constantly changing environmental conditions, and genetic characteristics.

Elementary (local) population- this is a collection of individuals of the same species, occupying small areas of a homogeneous territory.

The number of elementary populations in nature, the evolution of development and duration depend on the complexity and simplicity of the conditions in the biocenosis, its homogeneity.

In nature, the mixing of individuals of local populations erases the boundaries between them.

Ecological population- is formed as a set of local populations. Basically, these are intraspecific groups adapted to exist in a certain biocenosis. For example, common squirrel is widespread in various types of forests. Therefore, such ecological populations as “pine”, “spruce” can be distinguished. They are poorly isolated from each other, so there are few differences between them.

Geographic population - These are ecological populations that encompass a group of individuals that inhabit large territories with geographically homogeneous living conditions. Geographical populations are relatively isolated from each other and differ in fecundity, size of individuals, and a number of ecological, physiological, behavioral, and other features. Such prolonged isolation of a population can gradually lead to the formation of a geographic race or new species forms. Such species are usually considered as geographical speciation, race, or as a synonym for this species. For example, more than 20 geographical populations of common protein are known. The boundaries and sizes of populations in nature are determined by the characteristics of not only the inhabited territory, but also by the properties of the population itself. The research results of N.P. Naumov show that the division of the species into small territorial groups increases the diversity of the species and enriches its gene pool. Therefore, in nature there is no absolute population. Therefore, in the process of evolutionary development of each species during settlement (migration), they are constantly mixed with each other. In plants, pollen is widely distributed over long distances by wind. As a result, different forms of the population are maintained within the species. Therefore, from an environmental point of view, the population does not yet have a single definition. The definition of S. S. Schwartz deserves the greatest recognition: "A population is an intraspecific grouping, a form of existence of a species with certain quantitative and qualitative parameters."

The main indicators characterizing the population are abundance and density. The population is the total number of individuals in a given territory or in a given volume. The number of organisms is never constant. It depends on the birth rate and mortality of individuals.

Population density   determined by the number of individuals or biomass per unit area or volume, for example: 150 plants of spruce per 1 ha, or 0.5 g of daphnia in 1 m3 of water.

The population density varies depending on its size. The population density does not increase indefinitely, this requires the possibility of resettlement or free space. Resettlement continues until organisms encounter some kind of barrier. Distinguish between random, uniform and group distribution of populations.

FROMradial resettlement characteristic only for a homogeneous environment. For example, pests in the fields settle randomly, but then, as they multiply, the settlement acquires a group or spotty character.

Most common group resettlement, and it may be random. For example, in a forest, trees are distributed first in groups, and then evenly. In plants, distribution occurs when spores, seeds, fruits are spread, and in animals, the spread is fast and passive. For example, foxes, moose and other ungulates are very mobile. Slow spread occurs in sedentary animals.

In actively moving organisms, the ranges are huge, with no sharp boundaries between populations, while in inactive ones, on the contrary, the populations are clearly demarcated. These include amphibians, reptiles, mollusks. The size of the range of a population depends on the size of the organisms, activity of behavior, food supply and other abiotic factors. For example, in insects, herbaceous plants, the number of individuals can reach hundreds of thousands or more. On the contrary, the number and density of large animals and large woody plants are unstable and are associated with human activities. In addition, feed factors play a special role.

The decrease in feed yield in different years contributed to a sharp decrease in the dynamics of the population of squirrels, hares, muffins, pheasants. Therefore, in nature, the instability of the population is logical. However, in some cases, the population is replaced by a sharp drop or increase. These processes are common in nature. The reasons for their occurrence are many. This can be the gene pool of a species, environmental factors, growth rate, competition, excess food, etc.

A population in nature is capable of self-regulation of numbers. Each species has upper and lower limits for increasing the number beyond which it cannot go beyond. Therefore, the population size is kept at an optimal level. There are daily and seasonal fluctuations in the number of organisms. For example, in small animals, rodents, and some birds, fluctuations in numbers can be quite significant. So, it is known that the number of rodents increases during the season by 300-500 times, and some insects - by 1300-1500 times. Such outbreaks are often found in locusts, pathogens of infectious diseases, viruses and bacteria and cause enormous damage to agriculture and human life.

Sharp declines in population are inconsistent. In some cases, they lead to the extinction of the population. The total life span of organisms is divided into three types, i.e., there are three types of organisms survival (Scheme 6).

Scheme 6

I   - low mortality in the early stages of development and increased in the later stages (insects, large mammals); II - life expectancy is stable (some fish, birds, plants, etc.); III - maximum death in the early stages of development and low in adulthood (some fish, invertebrate animals)

Three types of survival.

The first type of survival is observed mainly in insects, large mammals, trees, and humans. Maximum death occurs in the last year (old age), where a large number of individuals have the same lifespan, and, of course, the first type of curve varies depending on genes, life expectancy, and sexual characteristics.

The second type is characteristic of organisms, where the mortality rate remains constant throughout life. These include the intestinal organisms of fresh water bodies.

The third type is common to most organisms. It is characterized by increased death of organisms in the early stages of development, for example: fish, birds, many invertebrates, characterized by fertility. Death among plants is 90-95%.

The obtained data on the patterns of survival of organisms play a large role in conducting theoretical studies and experiments with useful and harmful types of populations.

In addition to fertility and mortality, migration has a great influence on the population size or density. The population always seeks to expand its range. This mainly depends on the size and density of the younger generation. However, the population cannot expand its range indefinitely; limiting factors or adverse conditions of new habitats impede it.

There are stable, growing and shrinking populations. A balanced birth rate and mortality rate forms a stable population. In addition, the stability of a population depends on genetic, historical, biological conditions. In nature, the stability of a population also depends on birth and immigration, mortality, and emigration. Individuals appear in the population during immigration, decrease as a result of emigration.

Only with a balanced combination of these factors a stable population is formed. Knowledge of the structure and patterns of population development is of great practical importance.

Population. Elementary population. Ecological population. Geographical population. Population size. Population density. Accidental resettlement. Group resettlement. Three types of survival.

1. There are different views of environmental scientists on the problems of the population.

2. The main properties of the population - spatial distribution, abundance, density.

3. The fluctuation in the number of populations depends on environmental factors.

4.; There are three types of survival of organisms. Organisms with a high breeding potential (locusts, etc.) are found in nature.

1. What is a population?

2. How are populations classified?

3.How are the populations distributed?

1. What is the essence of the definitions of a population given by S. Schwartz, A. Yablokov, A. Gilyarov and N. Naumov?

2. What are the properties of the population and tell about their content.

1. What factors impede the widespread distribution of populations?

2. Which of the three types of survival does a person belong to?

3. Explain the types of survival of saigas and carp in the diagram.

1. How are saiga populations moving in Kazakhstan in winter and spring? Why?

2. How did populations of kulans appear in Kazakhstan and what do you know about their numbers?

Area   - part of the land surface or water area within which individuals of a given species (genus, family, or a certain type of community) are distributed and go through the full cycle of their development.

Endemic   - a species occupying a small territory.
  ■ Examples of endemic: relict plants of ginkgo and metasequoia, platypus, echidna, cysterae latimeria fish.

❖ Causes of Endemism:
  ■ geographical isolation (on oceanic islands, in mountainous regions or isolated bodies of water);
  ■ climatic and soil conditions;
  ■ biotic factors (competition, predation, symbiosis).

Cosmopolitan   - a species found on most of the inhabited areas of the Earth, widespread everywhere.
■ Examples of cosmopolitans:   weeds (large plantain, shepherd’s bag, etc.), water and marsh plants (duckweed, cattail), as well as housefly, city sparrow, gray rat and other animals that settle after the person.

❖ Factors affecting the formation and features of the range:
  ■ ecological plasticity of the species;
  ■ its ability to reproduce and resettle;
  ■ historical age;
  ■ speciation rate.

Continuous range   - This is an area within which species are found in all habitats suitable for their life.

Intermittent Range - This is an area that breaks up into several disparate territories, so remote from each other that the exchange of pollen or spores between plants or the migration of animals living in these territories is impossible.

Ecological niche species   Is a complex of living conditions of a species, i.e. the totality of all environmental factors (including the microclimate), within which the species can exist in nature.

■ Two species cannot occupy the same ecological niche; therefore, one of the species either creates a new ecological niche or disappears.

Populations and their main characteristics

Population   - this is a collection of individuals of one species, for a long time inhabiting a certain part of the range, relatively separate from other groups of individuals of the same species and interacting with each other (competing, helping each other, freely interbreeding, etc.).

■ Population is an elementary form of existence and evolution of a species.

The role of populations in evolution:   Due to the spatial fragmentation of the populations, the species exists in various environmental conditions and is exposed to natural selection of different intensities and in different directions, which leads to the formation of new varieties, subspecies and species of organisms.

The main characteristics of populations:   area, abundance, density, fertility, mortality, spatial, environmental, sexual and age structures, genetic heterogeneity.

The size of a stable population is limited by the maximum and minimum values.

■ The maximum population size is determined by environmental resources (amount of food, water, etc.).

■ The minimum population is at least several hundred individuals. With a smaller number, any random cause (fire, flood, drought, severe frosts, etc.) can lead to the extinction of the population.

Population homeostasis   - the property of a population to maintain its population at some optimal average level.

Population density   - the average number of individuals per unit area or volume of space occupied by the population.

As the number of individuals increases, population density tends to increase. It can remain unchanged only with the expansion of the range due to the resettlement of individuals.

Regulation of population density is achieved:

■ in plants   - due to intraspecific competition, leading to self-cutting (this changes not only the density, but also the vegetative power of individual individuals);

■ in animals through complex behavioral and physiological mechanisms, it manifests itself only in cases of limited environmental resources and the impossibility of their search in other territories (in small reservoirs where there are no other types of fish, adult perches feed on their own young).

Fertility (absolute)   - the number of new individuals in the population that appeared per unit time as a result of reproduction.

Birth rate   - the average number of individuals born in the population per unit time per 1, 100 or 1000 individuals of the population. This indicator allows you to compare the birth rate in populations with different numbers.

The birth rate of each species has been determined historically as an adaptation to compensate for the decline in populations and depends on:
  ■ sex ratios in a population (its sexual structure);
  ■ correlation of age groups (its age structure);
  ■ frequencies of reproductive cycles (reproduction cycles);
  ■ fertility of individuals (which, in turn, depends on the degree of development of care for the offspring and the provision of eggs with nutrients).

Usually, the birth rate in each population is balanced by its characteristic mortality.

Biotic potential   characterizes the theoretically possible number of offspring from one pair (or one individual) for a certain period of time (for example, for the entire life cycle or for a year).

■ Examples:   the number of many insects and crustaceans (aphids, daphnia) per year. may increase by 10 10 -10 30 times; the number of large mammals, even under the most favorable conditions, can increase by only 1.05-1.1 times per year.

Specific mortality   - the number of individuals killed in the population per unit time per one individual.

Survival curve   - A graph showing the percentage of individuals surviving to a particular age.

Types of organisms survival   (determined by mortality of individuals).
  ■ increased death of individuals in the early period of life (in fish);
  ■ uniform death of individuals at all periods of life (in hydra, some worms, etc.);
  ■ survival of individuals to an extreme age and mass death in later periods of life (most insects); less common; leads to outbreaks of reproduction.

Population structure

Spatial structure   population characterizes the features of the distribution of individuals on the occupied territory. It depends on the size of the population and its age and gender structure, can vary throughout the year and is determined by the habitat properties and biological characteristics of the species.

❖ Types of spatial structure of populations:
■ random   distribution over the territory;
■ uniform   distribution over the territory;
■ group   distribution when individuals live in groups: families, herds, colonies, harems. This distribution is most common, as it helps to better protect oneself from predators, to seek and obtain food.

Ecological structure   characterizes the attitude of various groups of organisms of one population to environmental conditions (for example, individuals of one plant population differ in size, number of leaves and flowers, do not bloom at the same time, their fruits also ripen not simultaneously, etc.).

■ This difference in individuals allows the population to survive as a whole when various adverse conditions occur, although one or another part of the individuals may die.

Sexual structure   expresses the ratio of the numbers of males and females in a population. As a rule, it differs from the 1: 1 ratio determined by the genetic mechanism, which is explained mainly by the different viability of males and females.

■ The predominance of the proportion of females over males provides a more intensive population growth.

■ Since males and females of many species differ in the nature of their nutrition, behavior, etc., a change in the sexual structure of a population to one degree or another changes its role in the ecosystem.

■ In human populations, the sex ratio at birth is 100 girls per 106 boys, by the age of 18 it becomes 1: 1, by 50 years old there are 85 men per 100 women, by 80 years the sex ratio becomes 2: 1 (100 women for 50 men).

Age structure of the population   reflects the ratio of different age groups in the population. It depends on the life expectancy of individuals, the time of onset of their puberty, the number of offspring in the litter, the number of offspring per season, etc.

■ The presence in the population of a large number of individuals of younger age groups indicates its well-being. The prevalence in the population of old individuals suggests that this population ends its existence.

■ The age structure reflects the adaptive nature of individuals, since the environmental resistance of individuals of different ages is not the same (adult May beetles live for several weeks, and their larvae in the soil for three years).

❖ Types of ecological age:
  ■ pre-reproductive;
  ■ reproductive;
  ■ post-reproductive.

Population dynamics

Population growth - this is the difference between birth rate and. mortality. It can be positive (the population is increasing) and negative (the population is decreasing).

Growth rate   - average population growth per unit time. In most species, it depends on population density. The highest growth rate is observed at a certain optimal population density or when a population enters a new, unoccupied ecological niche.

Population growth.   Any population, if it is not limited by environmental factors (limited resources, diseases, predators, etc.), is theoretically capable of unlimited population growth. In this case, the rate (rate) of population growth depends only on the value biotic potential , and the population growth itself occurs exponentially (called exponentially) and is called exponential.

Exponential growth conditions. A real exponential increase in population size can occur only for a limited period of time in the following cases:

■ the population is in conditions of an excess of environmental resources (food, breeding sites) and is not affected by adverse factors;

■ the population falls into new conditions where it does not have enemies and competitors (example: rabbits in Australia);

■ the population exists in artificially created laboratory conditions (bacteria, yeast, etc.).

An increase in the population leads to an increase in its density. But as the population density increases, the limited resources of the environment begin to affect, and the conditions for reproduction and growth of individuals become less favorable, which leads to a slowdown in population growth.

Logistic type of population growth   - type of growth with limited resources, characterized by a decrease in growth rate with increasing population density.

Medium capacity   - optimal population density in specific environmental conditions.

■ If the population density corresponds to the capacity of the medium, then the population size will fluctuate around the average level.

■ If the population density exceeds the capacity of the medium, then the population size and density are reduced.

Regulation of the population.Two groups of factors affecting population size:

■ modifyingthat are independent of population density (this is usually abiotic   environmental factors; for example, severe winter leads to the death of animals and birds feeding on the ground, etc.);

■ regulatorydepending on population density (as a rule, these are different biotic factors: fertility, mortality, migration, behavioral factors, exhaustion of environmental resources, etc.).

Migrations   - these are regular daily or seasonal movements of animals between essentially different, spatially separated habitats. They are caused by changes in living conditions in habitats or by changes in the requirements of animals for these conditions at different stages of development.

The role of migrations:

■ allow organisms for some time to use the optimal environmental conditions in those places where the permanent residence of organisms of this species is impossible;

■ lead to the development of new biotopes and the expansion of the general range of the species;

■ lead to the exchange of individuals between populations, which can change their structure and basic properties, prevent the death of a population on the verge of extinction, or, conversely, lead to a sharp reduction;

■ increase the unity and overall stability of the species;

■ contribute to success in the struggle for existence.

In the absence of migration, a change in population size depends on the ratio of fertility to mortality.

Examples of physiological and behavioral factorsgoverning the size and density of the population:

■ With a high population density in some animal species (rodents), the concentration of adrenaline hormone in the blood increases, causing aggression (fights) and various hormonal disorders (in the females, the embryo may resorb), which ultimately leads to a decrease in the population;

■ chemical interaction   individuals (eg. example, tadpoles release substances into the water that inhibit the growth of other tadpoles);

■ tagging   (secret of odorous glands, scratches on trees, singing of male birds, etc.), security   individual area and prevent   breeding on it of “alien” individuals allows the most rational use of the space occupied by the population. The excess part of the population does not reproduce or is forced to move out of the occupied space.

The multiplicity of mechanisms for regulating numbers leads to the fact that in nature very rarely there is a catastrophic increase in numbers, undermining resources (lack of food, shelters, space) and the death of the population.

Abundance and density are the main parameters of the population.

Number   - the total number of individuals in a given territory or in a given volume.

  Density    - the number of individuals or their biomass per unit area or volume. In nature, there are constant fluctuations in numbers and density.

Population dynamics and density is determined mainly by fertility, mortality and migration processes. These are indicators characterizing the change in the population over a certain period: month, season, year, etc. The study of these processes and their underlying causes is very important for predicting the state of populations.

Fertility is distinguished between absolute and specific. Absolute birth rate Is the number of new individuals that appeared per unit of time, and specific- the same number, but assigned to a certain number of individuals. For example, a person’s birth rate is the number of children born per 1,000 people during the year. Fertility is determined by many factors: environmental conditions, food availability, species biology (puberty rate, number of generations during the season, ratio of males and females in the population).

According to the rule of maximum fertility (reproduction) under ideal conditions, the maximum possible number of new individuals appears in populations; fertility is limited by the physiological characteristics of the species.

Example: Dandelion in 10 years is able to fill the entire globe, provided that all its seeds sprout. Extremely abundant seeds of willow, poplar, birch, aspen, most weeds. Bacteria divide every 20 minutes and for 36 hours can cover the entire planet with a continuous layer. Fertility is very high in most species of insects and low in predators, large mammals.

Mortality,   like fertility, it is absolute (the number of individuals that died in a certain time), and specific. It characterizes the rate of population decline from death due to diseases, old age, predators, lack of food, and plays a major role in the dynamics of the population.

There are three types of mortality:

The same at all stages of development; It is rare in optimal conditions;

Increased mortality at an early age; characteristic for most species of plants and animals (less than 1% of seedlings survive by age of maturity in trees, 1-2% of fry in fish, less than 0.5% of larvae in insects);

High death in old age; usually observed in animals whose larval stages pass under favorable slightly changing conditions: soil, wood, living organisms.

Stable, growing and shrinking populations

The population adapts to changing environmental conditions by updating and replacing individuals, i.e. processes of birth (renewal) and decrease (death), complemented by migration processes. In a stable population, the birth and death rates are close and balanced. They may be unstable, but the population density is slightly different from some average value. The range of the species is neither increasing nor decreasing.

In a growing population, fertility exceeds mortality. Growing populations are characterized by outbreaks of mass reproduction, especially in small animals (locusts, 28-point potato bugs, Colorado potato beetles, rodents, crows, sparrows; from plants - ragweed, Sosnowski hogweed in the northern Komi Republic, dandelion, Himalayan, partly oak) Mongolian). Populations of large animals often grow under the conditions of the conservation regime (elk in the Magadan reserve, Alaska, sika deer in the Ussuri reserve, elephants in the Kenya national park) or introductions (elk in the Leningrad region, muskrat in Eastern Europe, domestic cats in separate families) . When re-compaction in plants (usually coincides with the onset of closure of the cover, crown canopy), differentiation of individuals in size and state of life begins, self-thinning of populations, and in animals (usually coincides with the achievement of puberty of young animals), migration to adjacent free areas begins.

If mortality exceeds fertility, then such a population is considered declining. In the natural environment, it is reduced to a certain limit, and then the birth rate (fertility) again increases and the population from the declining becomes growing. Most often, populations of undesirable species are excessively growing, declining - rare, relic, valuable, both economically and aesthetically.

Population structure

Under demographic structure   populations, first of all, understand its gender and age composition. In addition, it is customary to talk about spatial structure   population - that is, about the features of the distribution of individuals in space.

Knowledge of the structure of the population allows the researcher to draw conclusions about its well-being or disadvantage. For example, if in a population there are no generative (that is, able to give offspring) individuals and there are many old-aged (senile) individuals, then an unfavorable prognosis can be made. Such a population may not have a future. It is desirable to study the structure of the population in dynamics: knowing its change over several years, one can speak much more confidently about certain trends.

Age structure of the population

This type of structure is associated with the ratio of individuals of different ages in the population. Individuals of the same age are usually combined in cohorts, that is, age groups.

The age structure of plant populations is described in great detail. The following ages (age groups of organisms) are distinguished in it (according to T.A. Robotnov):

• latent period - the state of the seed;
• pregenerative period (includes the conditions of a seedling, juvenile plant, immature plant and virgin plant);
• generative period (usually divided into three subperiods - young, mature and old generative individuals);
• postgenerative period (includes the state of the sub-senile plant, senile plant and the dying phase).

In animal populations, various age stages can also be distinguished. For example, insects that develop with complete metamorphosis go through the stages of an egg, larva, pupa, and adult (adult insect). In other animals (developing without metamorphosis), various age-related states can also be distinguished, although the boundaries between them may not be so clear.

Sexual structure of the population

The sexual structure, that is, the sex ratio, is directly related to the reproduction of the population and its stability.

It is customary to distinguish the primary, secondary and tertiary sex ratios in the population. Primary sex ratio   determined by genetic mechanisms - the uniformity of the divergence of sex chromosomes. For example, in humans, the XY chromosomes determine the development of the male, and XX - the female. In this case, the primary sex ratio is 1: 1, that is, it is equally probable.

Secondary sex ratio - This is the sex ratio at the time of birth (among newborns). It can differ significantly from the primary one for a number of reasons: the selectivity of the ovum to spermatozoa bearing the X- or Y-chromosome, the unequal ability of such sperm to fertilize, and various external factors. For example, zoologists describe the effect of temperature on the secondary sex ratio of reptiles. A similar pattern is typical for some insects. So, in ants, fertilization is provided at temperatures above 20 ° C, and at lower temperatures unfertilized eggs are laid. Males hatch from the latter, and females from the fertilized ones — predominantly.

Tertiary sex ratio   is the sex ratio among adult animals.

Spatial structure of the population

The spatial structure of the population reflects the nature of the distribution of individuals in space.

There are three main types of distribution of individuals in space:

• uniform   (individuals are distributed uniformly in space, at equal distances from each other), the type is also called uniform distribution;
• congregational, or mosaic (that is, "spotted", individuals are located in isolated clusters);
• random, or diffuse (individuals are randomly distributed in space).

Uniform distribution is rare in nature and is most often caused by intense intraspecific competition (as, for example, in predatory fish).

Random distribution can be observed only in a homogeneous environment and only in species that do not show any desire for grouping. As a textbook example of uniform distribution, the distribution of the Tribolium beetle in flour is usually given.

Group distribution is much more common. It is associated with the characteristics of the microenvironment or with the features of the behavior of animals.

The spatial structure is of great environmental importance. First of all, a certain type of use of the territory allows the population to efficiently use environmental resources and reduce intraspecific competition. Efficiency of using the environment and reducing competition between representatives of the population allow it to strengthen its position in relation to other species inhabiting this ecosystem.

Another important value of the spatial structure of the population is that it provides for the interaction of individuals within the population. Without a certain level of intrapopulation contacts, the population will not be able to perform both its species functions (reproduction, resettlement) and the functions associated with participation in the ecosystem (participation in the circulation of substances, creation of biological products, and so on).

Population Properties:   self-reproduction, variability, interaction with other populations, sustainability.



The biological term “population” was first used in 1903 by a biologist from Denmark Wilhelm Ludwig Johansen (1857 - 1927)   to indicate the group growth of one plant species.

In contact with

General concept

What is a population? She (the ancient Latins said:   populusfrom modern English. population- population) is a collection of representatives   a specific type of living organism, a long time span of living or growing in one territorial space, apart from individuals of other groups similar in similar characteristics.

The term is used in various fields of natural sciences: ecology, medicine, demography.

If we take for example, then in appropriate terminology, the concept   defined as a community of animals or plants of the same species having a single gene pool   (we will consider this term below), capable of sustainable self-reproduction. In biology, it means groups of organisms in a particular species.

The simplest example is the human population on Earth. If we take examples from the animal world: sika and red deer, brown and polar bears, cod and haddock in the seas of the Arctic Ocean basin. From the plant world: different species of pine and spruce, aspen and linden, oak and elm.

What are the characteristics of each population? Common criteria are:

• general habitat (range);
• the uniform origin of a community of organisms;
• the relative isolation of this community from other similar groups (the so-called interpopulation barriers);
• compliance with the principle of panmixia (free crossing) as part of a group, in other words, the equal probability of meeting all existing genotypes within the range.

Types of populations

There are a lot of species of living organisms in the wild. First of all, it is necessary to highlight two global populations   - animals and plants. And already in them subspecies of one or another specific group of organisms are determined

In biology, geographically determined groups are structurally distinguished, as an example, the settlement of squirrels in the forests of the Ulyanovsk region. Grouped animals of the same subspecies (in our case, squirrels) living in a geographically homogeneous space. This area is called the habitat.

In turn, geographic populations are subdivided into smaller ones - ecological ones (proteins in coniferous and mixed forests of the same region), and those into even smaller ones - elementary or local (the same proteins, but already in different parts of the same forest).

By the ability to reproduce, there is a division into:

• Permanentthat do not need an influx of individuals of their own species from outside to maintain their numbers at the level necessary for a full-fledged existence.
• Semi-dependent, in which a certain number of such individuals from outside comes from outside, but even without them the population is able to exist for a long time.
• Temporary, in them the mortality of representatives is higher than the specific birth rate, and existence is directly dependent on the influx of individuals from outside. Temporary populations are often formed in places with an unfavorable climate and an unstable food supply.

Attention!The population is very similar to a living organism, as a biosystem, also has an organized structure with its own integrity, a genetic program of self-reproduction and special characteristic mechanisms of self-regulation and adaptation.

Population structure

The structure of the predominant number of existing species settlements is determined by the representatives that form them, and the location of the latter in the habitat (remembering the squirrel - the total number and percentage of heterosexual animals in the forest). To make it clearer, consider the points.

So, the structure of the population happens

Spatial - the distribution of individuals over the occupied area - how many squirrels run and where. It, in turn, is divided into:

• Random (if the forest is the same for all squirrels, and they jump in the same natural setting). In this case, there are few animals, they do not stray into the “groups” and do not live in a heap of water.
• Uniform. It occurs mainly in animals living in conditions of fierce competition for feed resources and habitats. Some species of carnivorous fish, birds, and mammals (bears, for example) guard their hunting grounds with care and do not favor strangers on them.
• Group The most common in nature. Here we consider the example of plants. Some trees have large, heavy fruits (nuts, acorns, plane nuts, etc.), which fall next to the tree and sprout immediately, forming groups. And even lilies of the valley! But, they are obliged to this vegetative method of reproduction (offspring from rhizomes). These growing patterns are caused   the fact that the environmental conditions are heterogeneous, habitats are limited, the species has characteristic biological qualities and reproduction options.

Sexual - the ratio of heterosexual specimens (how many squirrel-boys and squirrel-girls are in the forest).

Age - the most understandable. How many individuals of different ages. In any species, and sometimes, in each population within a species, there are different ratios of age groups. As a rule, the following environmental ages are distinguished:

• pre-reproductive (organisms under puberty);
• reproductive (mature);
• post-reproductive (representatives who have lost the ability to reproduce).

For animals and plants, this structure has significant differences, but this is a separate topic for consideration.

Genetic structure of the population due to the variability and diversity of genotypes(roughly speaking the difference in protein in color and size, and their variations when mating with subsequent offspring).

The ecological structure consists in the division of a species into groups of individual representatives, interacting in their own way with the environment. It is here that the local population is often manifested. The thing is that the difference between the type and a separate group of representatives existing in the special conditions of the general area of \u200b\u200bresidence is very arbitrary.

Basically, the system functions like   almost any biological system.   Accordingly, it is characterized by: growth, development, survival in changing environmental conditions. This leads to the presence of certain parameters.

Protein population

Parameters

Most existing populations are characterized by:   abundance, density, birth rate and mortality. All these characteristics, moreover, are closely interconnected and interdependent.

Population size   - the total number of representatives of the species living in the territory. Density, respectively, the number of individuals of a given species per unit area of \u200b\u200bhabitat.

In many large groups, the average abundance does not change much annually, due to the fact that:

• from natural causes, approximately the same number of representatives die;
• the reproduction rate of organisms increases with a small population density, and with an increase, accordingly, decreases;
• constantly changing environmental conditions and climatic factors create obstacles to the high realization of reproductive potential.

But, even with a certain stability, fluctuations are characteristic of the population. The main reasons for these fluctuationsassociated with changes in living conditions. Namely:

These periodic fluctuations lead to changes in the total number, which consist of the following phenomena:

• birth rate;
• mortality;
• immigration (introduction - an influx of individuals from the outside);
• emigration (eviction of the species).

These factors are associated with the so-called population waves.

Important!Population waves - sudden significant numerical changes.

Example: a reduction in the number of foxes caused by shooting (abiotic factor) leads to a population increase in field mice (field voles).

Populations are characterized by abundance, density, fertility and mortality.

Gene pool

But of particular importance is the effective number - the number of sexually mature representatives of the species that can produce offspring. They form the gene pool. And now consider this concept specifically.

What is a population gene pool(gene pool). This is the totality of all the traits (genes) of the species and their variations, inherited. Thanks to genes, proteins from Siberia are different from proteins from Canada. Gene variations (alleles) determine the ability of organisms to adapt to constantly changing environmental features. The greater the diversity of genes, the more capable the body is to adapt to life.

In biology, there is such a thing as an ideal population. But, it is purely theoretical and is used to model processes. Perfect populationcan be defined as a hypothetical panmictic (i.e., individuals of which have equal chances of interbreeding), with infinitely growing, preserved in generations, and independent of natural selection, external factors and mutations, numbers.

What is the main role of the concept for the existence of living organisms on the planet? In ecology, it is defined as an elementary unit of a process microevolution(intraspecific small gene changes in several generations, leading to certain changes in the individual, both external and internal), responding to changing environmental factors by restructuring the gene pool.

The functioning of the population and the dynamics of its abundance in nature

Population as a form of existence of species in nature

Conclusion

Based on the foregoing ,   summarize. A population is a collection of representatives of one species living on a common territory, freely crossing, having a single gene pool, having its own structure, characteristics and parameters similar to existing biosystems, and is an elementary microevolutionary unit.