1. The concept of a population: statistical indicators of a population, the concepts of genotype and gene pool

A set of individuals that have a hereditary similarity of morphological, physiological and biochemical features, capable of crossing with the formation of fertile offspring, adapted to certain living conditions and occupying a certain territory (range) in nature, is called a biological species. Species often occupy a large area, within which individuals are distributed unevenly, in groups - populations.

A population is a collection of individuals of the same species capable of self-reproduction, which exists for a long time in a certain part of the range relatively apart from other populations of the same species. The term "population" comes from the Latin word "populus" (people) and literally means "population". The population is precisely that cell of the biota, which is the basis of its existence: self-reproduction of living matter takes place in it, it ensures the survival of the species, i.e. is the structural unit of the species and the unit of evolution. Contacts between individuals of the same population occur more frequently than between individuals of different populations. For example, the level of panmixia (free crossing) within a population is higher than between individuals from different populations.

Area. The space in which a population or species as a whole occurs throughout its life is called an area - a distribution area. The range can be continuous or broken (disjunctive) if various barriers (water, orographic, etc.) arise between its parts, spaces not inhabited by representatives of this species.

2.Statistical indicators of the population

Quantitative indicators (characteristics) of the population can be divided into static and dynamic. Static indicators characterize the state of the population on this moment time. The main ones are: the number and density, as well as indicators of the structure. The dynamic indicators of a population reflect the processes occurring in the population over a certain period of time. The main ones are: birth rate, death rate, population growth rate.

The number is the number of animals or plants within a certain spatial unit: range, river basin, sea area, region, district, etc. Population size can change significantly over time. It depends on the biotic potential of the species and external conditions. The number of certain animals is determined by various methods. For example, counting from an airplane or helicopter during overflights of the territory. The size of the human population is determined by a census of the population of the entire state, its administrative divisions. The importance of the size and structure of the population (ethnic, professional, age, gender, etc.) is of great economic and environmental importance.

Density is the number of individuals or biomass of a population per unit area or volume. The larger the animal, the more area it needs to get food, therefore, the larger the body size of the individual, the lower the population density.

The population is characterized by a certain structural organization - the ratio of groups of individuals by sex, age, size, distribution of individuals over the territory, etc. In this regard, various population structures are distinguished: sex, age, size, genetic, spatial and ethological, etc. The population structure is formed, on the one hand, on the basis of the general biological properties of the species, on the other hand, under the influence of environmental factors.

Sexual structure (sex composition) - the quantitative ratio of male and female individuals in a population. The sex ratio of a population is established according to genetic laws as a result of the recombination of sex chromosomes, and then it is influenced by the environment. Theoretically, the sex ratio should be the same: 50% of the total number should be males, and 50% females. The actual sex ratio depends not only on the genetic and physiological characteristics of the species, but also on the action of various environmental factors (for example, in fish - on the pH value of the environment; in red forest ants from eggs laid at temperatures below 20 ° C, males develop, and at higher temperatures, females).

There are primary, secondary and tertiary relationships. The primary ratio is the ratio observed during the formation of germ cells (gametes). Usually it is 1:1. This ratio is determined by the genetic mechanism of sex determination. Secondary ratio - the ratio observed at birth. Tertiary ratio - the ratio observed in adult sexually mature individuals.

For example, in a person in the secondary ratio, boys somewhat predominate, in the tertiary ratio - women: 100 girls are born for 106 boys, by the age of 16 ... and by the age of 80 - 50 men and 100 women.

The genetic structure of a population is characterized by varying degrees of genetic diversity of individuals. The totality of all genes concentrated in the chromosomes of one organism is called the genotype. If the ratio of genotypes in a population is unchanged in generations, then the population is stable, there is a genotypic equilibrium in it. The totality of genes that individuals of a particular population have is called the gene pool. Despite the variability in its structural parts, the population as an integral system stably preserves the gene pool inherited from the ancestral population.

The relative spatial isolation of a population leads to its reproductive isolation - the restriction of the freedom of interbreeding of individuals from different populations. This isolation ensures the uniqueness of the gene pool of the population and the possibility of its independent evolution. However, in nature there are no completely isolated populations and migration (outflow and inflow) of genes can occur, leading to changes in their genetic structure.

Age structure (age composition) - the ratio in the population of individuals of different age groups. The absolute age composition expresses the number of certain age groups at a certain point in time. Relative age composition expresses the proportion or percentage of individuals of a given age group in relation to the total population. The age composition is determined by such indicators as: the time to reach puberty, life expectancy, the duration of the breeding season, mortality, etc.

Depending on the ability of an individual to reproduce, three groups are distinguished: pre-reproductive (individuals that are not yet able to reproduce), reproductive (individuals that are able to reproduce) and post-reproductive (individuals that are no longer able to reproduce).

The ratio of individuals in the population for these states is called the age spectrum of the population, which reflects the quantitative ratios of different age groups. The ability of the population to self-maintenance and its resistance to external influences is assessed by the age spectrum. To compare the number of individuals of different ages in populations, histograms of age structures are constructed (see Fig.).

Populations in which all ages are represented relatively evenly are distinguished by the greatest viability. Such populations are called normal. If the population is dominated by senile individuals, this indicates the presence of negative factors that disrupt reproductive functions. Such populations are called regressive, or endangered.

Age structure of populations:

Invasive (growing); 2 - normal (stable);

Regressive (shrinking)

Populations represented mainly by young individuals are considered as invading or invasive. Their vitality does not cause concern, but there is a high probability of outbreaks of an excessively high number of individuals. It is especially dangerous if such populations are represented by species that were previously absent here.

The spatial-ethological structure determines the nature of the distribution of individuals within the range. It depends on the characteristics environment and ethology (behavioral features) of the species.

There are three main types of distribution of individuals in space: uniform (regular), uneven (aggregated, group, mosaic) and random (diffuse).

In a uniform distribution, individuals are placed at more or less equal intervals, such as trees in a pine forest. In reality, a uniform distribution of individuals is rarely found in nature.

Uneven (group, mosaic) distribution is manifested in the formation of groups of individuals, between which large uninhabited territories remain. It is typical for populations living in conditions of uneven distribution of environmental factors or consisting of individuals leading a group lifestyle (for example, herds of mammals, bird colonies). Group placement provides populations with higher resistance to adverse conditions.

With a random (diffusion) distribution, individuals are distributed unevenly, and their meetings with each other are random. This type of distribution is widespread among plants and many animal species. Random distribution is the result of probabilistic processes and weak social connections between individuals.

Over large geographic areas, over time, individuals of the same population, when distributed, can form combinations of these three types of distribution. For example: trees - from group to uniform. The resettlement of aphids or the Colorado potato beetle may initially be random, and as they reproduce, it acquires a group or uniform character.

According to the type of use of space, all mobile animals are divided into sedentary and nomadic. The settled way of life is characterized by an intensive type of use of the territory, i.e. individual individuals or their groups exploit resources in a relatively limited space for a long time. It has a number of biological advantages, such as free orientation in familiar territory when looking for food or shelter, the ability to create food supplies (squirrels, field mice). Its disadvantages include the depletion of food resources at an excessively high population density.

Species characterized by a nomadic way of life are characterized by an extensive type of territory use, in which resources are usually consumed by groups of individuals constantly moving within a vast area.

According to the form of the joint existence of animals, a solitary lifestyle, family, colonies, flocks, herds are distinguished.

The spread of organisms outside a population is called dispersal. Dispersal patterns reflect how a population occupies more and more space. Among them, the following are distinguished: anemochory (spread by wind), hydrochory (by water), phytochory (by plants), zoochory (by animals) and anthropochory (by humans).

3. Aquatic life environment

From an ecological point of view, the environment -These are natural bodies and phenomena with which the organism is in direct or indirect relations. Habitat is a part of nature that surrounds living organisms (individual, population, community) and has a certain impact on them.

On our planet, living organisms have mastered four main habitats: aquatic, terrestrial-air, soil and organismal (i.e., formed by living organisms themselves).

Aquatic life environment

The aquatic environment of life is the most ancient. Water ensures the flow of metabolism in the body and the normal functioning of the body as a whole. Some organisms live in water, others have adapted to a constant lack of moisture. The average water content in the cells of most living organisms is about 70%.

4. Specific properties of water as a habitat

A characteristic feature of the aquatic environment is the high density -it is 800 times the density of the air. In distilled water, for example, it is 1 g/cm 3. With increasing salinity, the density increases and can reach 1.35 g/cm 3. All aquatic organisms experience high pressure, increasing by 1 atmosphere for every 10 m of depth. Some of them, such as anglerfish, cephalopods, crustaceans, starfish and others, live at great depths at a pressure of 400 ... 500 atm.

The density of water provides the ability to rely on it, which is important for non-skeletal forms of aquatic organisms.

The biont of aquatic ecosystems is also affected by the following factors:

1.concentration of dissolved oxygen;

2.water temperature;

.transparency, characterized by a relative change in the intensity of the light flux with depth;

.salinity, that is, the percentage (by weight) of salts dissolved in water, mainly NaCl, KC1 and MgSO4 ;

.availability nutrients, primarily compounds of chemically bound nitrogen and phosphorus.

The oxygen regime of the aquatic environment is specific. There is 21 times less oxygen in water than in the atmosphere. The oxygen content in water decreases with increasing temperature, salinity, depth, but increases with increasing flow velocity. Among hydrobionts, there are many species belonging to euryoxybionts, i.e., organisms that can tolerate low oxygen content in water (for example, some types of mollusks, carp, crucian carp, tench, and others).

Stenoxybionts, such as trout, mayfly larvae, and others, can exist only with a sufficiently high saturation of water with oxygen (7 ... 11 cm 3/l), and therefore are bioindicators of this factor.

The lack of oxygen in water leads to catastrophic phenomena. -kills (winter and summer), accompanied by the death of aquatic organisms.

Temperature regime the aquatic environment is characterized by relative stability compared to other media. In fresh waters temperate latitudes the temperature of the surface layers ranges from 0.9 °C to 25 °C, i.e. the amplitude of temperature changes is within 26 °C (except for thermal sources, where the temperature can reach 140 °C). At a depth in fresh water bodies, the temperature is constantly equal to 4 ... 5 ° C.

The light regime of the aquatic environment differs significantly from the ground-air environment. There is little light in water, as it is partially reflected from the surface and partially absorbed when passing through the water column. The passage of light is also hindered by particles suspended in water. In deep reservoirs, in connection with this, three zones are distinguished: light, twilight and the zone of eternal darkness.

According to the degree of illumination, the following zones are distinguished:

littoral zone (water column where sunlight reaches the bottom);

limnic zone (water column to a depth where only 1% of sunlight penetrates and where photosynthesis fades);

euphotic zone (the entire illuminated water column, including the littoral and limnic zones);

profundal zone (bottom and water column where sunlight does not penetrate).

In relation to water, the following ecological groups are distinguished among living organisms: hygrophiles (moisture-loving), xerophiles (dry-loving) and mesophiles (intermediate group). In particular, among plants, hygrophytes, mesophytes and xerophytes are distinguished.

Hygrophytes -plants of moist habitats that do not tolerate water deficiency. These include, for example: pondweed, water lily, reed.

Xerophytes plants of dry habitats, able to tolerate overheating and dehydration. There are succulents and sclerophytes. succulents -xerophytic plants with succulent, fleshy leaves (for example, aloe) or stems (for example, cacti) in which water storage tissue is developed. Sclerophytes are xerophytic plants with hard shoots, due to which, with a water deficit, they do not have an external wilting pattern (for example, feather grass, saxaul).

Mesophytes -plants of moderately humid habitats; intermediate group between hydrophytes and xerophytes.

About 150,000 species of animals live in the aquatic environment (which is about 7% of their total number) and 10,000 plant species (which is about 8% of their total number). Organisms that live in water are called hydrobionts.

Aquatic organisms according to the type of habitat and lifestyle are combined into the following ecological groups.

Plankton -Suspended organisms hovering in the water, passively moving due to the current. There are phytoplankton (single-celled algae) and zooplankton (single-celled animals, crustaceans, jellyfish, etc.). A special kind of plankton is the ecological group neuston -inhabitants of the surface film of water at the border with the air (for example, water striders, bedbugs, and others).

Nekton -animals actively moving in the water (fish, amphibians, cephalopods, turtles, cetaceans, etc.). Active swimming of hydrobionts united in this environmental group directly depends on the density of water. Rapid movement in the water column is possible only in the presence of a streamlined body shape and highly developed muscles.

Benthos -organisms living on the bottom and in the ground, it is divided into phytobenthos (attached algae and higher plants) and zoobenthos (crustaceans, mollusks, starfish, etc.).

5. Varieties of smog and their features

Smog (eng. Smoke - smoke, fog - thick fog) - visible air pollution of any nature. Smog occurs under certain conditions: in large numbers dust and gases in the air and the long existence of anticyclone weather conditions (areas with high atmospheric pressure) when pollutants accumulate in the surface layer of the atmosphere. Smog causes suffocation, asthma attacks, allergic reactions, eye irritation, damage to vegetation, buildings and structures.

There are three types of smog: ice (Alaskan type); wet (London type); dry or photochemical (Los Angeles type).

Wet smog is the most studied. It is common in places with high relative humidity and frequent fogs. This contributes to the mixing of pollutants, and the interaction of chemical reactions. These pollutants are directly released into the atmosphere, they are called primary pollutants. The main toxic components of wet smog are most often CO 2and SO 2. The case when in 1952 damp smog in London claimed more than 4000 lives is notorious.

Photochemical smog is a secondary air pollution that occurs during the decomposition of primary pollutants by sunlight. The main toxic component is ozone.

Ice smog occurs when low temperatures and anticyclone. In this case, emissions of even a small amount of pollutants lead to the formation of a thick fog consisting of tiny ice crystals and, for example, sulfuric acid.

Air is basically a mixture of O 2and N 2. At a high flame temperature, molecules in air can disintegrate, and even molecules of the relatively inert N 2undergo reactions:

According to the equation, an oxygen atom is formed, which enters the equation. Once an oxygen atom has arisen in a flame, it will be recreated and participate in the entire reaction chain leading to the formation of NO. If we sum these two reactions, we get:

The equation shows how nitrogen oxides are formed in a flame. They appear because the fuel is burned in air and not in oxygen O 2. In addition, some fuels contain nitrogen compounds as impurities, and as a result, the combustion products of these impurities serve as a source of other nitrogen oxides. Oxidation of nitric oxide in smog produces nitrogen dioxide, a brown gas. This color means that the gas absorbs light (with a wavelength of at least 310 nm), is photochemically active and undergoes dissociation:

Thus, according to the equation, nitric oxide reappears, but also a single and reactive oxygen atom, which can react to form ozone - O3 :

Ozone is the only pollutant that most clearly characterizes photochemical smog. However, O 3, which presents such a problem, is not emitted by the car (or any major pollutant). This is a secondary pollutant.

So, volatile organic compounds released due to the use of gasoline-based fuels contribute to the conversion of NO to NO 2(and underlie photochemical smog).

In the process of hydrocarbon oxidation in the atmosphere, the role of the OH* radical should be especially noted. Consider the oxidation of methane (CH 4) as a simple example of this process:

These reactions show the conversion of nitric oxide (NO) to dioxide (NO 2) and a simple alkane of the type CH 4to an aldehyde (in this case formaldehyde HCHO). In this case, the OH* radical is reproduced at the end of the chain of reactions, so it can be considered a catalyst in some way. Despite the fact that the reaction takes place in photochemical smog, the effect of the OH* radical on large and complex organic molecules is quite effective. Aldehydes can also be attacked by OH* radicals.

Methyl radical (CH 3*) from the equation can return to the equation.

An important addition to this series of reactions is the following:

leading to the formation of peroxyacetyl netrate (PAN), which is irritating to the eye.

6. Environmental law and its main sources

Environmental law is a branch of law that regulates social relations in the field of interaction between society and nature.

Environmental law is an important tool used by the state in the interests of conservation and rational use of the environment. natural environment.

The sources of environmental law are the following legal acts: 1) The Constitution Russian Federation; 2) laws and codes in the field of nature protection; 3) decrees and orders of the President on issues of ecology and nature management; government environmental regulations; 4) normative acts of ministries and departments; 5) normative decisions of local self-government bodies.

1. The constitutional foundations for the protection of the natural environment are enshrined in the Constitution of the Russian Federation, adopted on December 12, 1993. The Constitution proclaims the right of citizens to land and other natural resources, establishes the right of every person to a favorable environment (environmental safety) and to compensation for damage caused to his health. It also defines the organizational and control functions of higher and local authorities for the rational use and protection of natural resources, establishes the duties of citizens in relation to nature, the protection of its wealth.

2. Laws and codes in the field of environmental protection constitute the natural resource legal basis. These include laws on land, subsoil, atmospheric air protection, on the protection and use of wildlife, etc. The system environmental legislation heads the Federal Law "On Environmental Protection" dated January 10, 2002 No. 7-FZ. In matters of environmental protection, the norms of other laws must not contradict the Constitution of Russia and this legislative act.

1. The Land Code of the Russian Federation (2001) regulates the protection of land and the protection of the natural environment from possible harmful effects when using land. The main legal functions of land protection are: preservation and improvement of soil fertility, preservation of the fund of agricultural lands. Damage, pollution, clogging and depletion of land are considered environmental violations. The Code regulates the purchase and sale of land and other land transactions.

2. The Water Code of the Russian Federation (1995) regulates legal relations in the field of rational use and protection of water bodies, establishes liability for violation of water legislation. Legal norms are aimed at protecting water from pollution, clogging and depletion.

3. The legal basis for the protection of atmospheric air is reflected in the Law of the Russian Federation "On Environmental Protection" (2002), as well as the Law "On the Protection of Atmospheric Air" (1982). The most important general measures for the protection of the air basin are the establishment of standards for maximum permissible harmful effects (MAC, MPE) and fees for emissions of pollutants into the atmosphere.

4. Legal protection of people involved in the use of nuclear and radiation installations and radioactive substances is guaranteed by the Law of the Russian Federation "On Radiation Safety of the Population" (1995) (as well as the Federal Law "On the Use of Atomic Energy").

In the event of an accident, the Law guarantees compensation for damage to the health and property of citizens, establishes compensation for the increased risk of those living near nuclear and radiation installations in the form of improved social and living conditions.

5. The Law of the Russian Federation "On Subsoil" (1992) establishes legal relations in the study, use and protection of subsoil. Among the environmental and legal violations affecting the subsoil as part of the natural environment, the Law primarily refers to their pollution.

6. Fundamentals of forest legislation (1977) fix the requirements for forest management. The main legal norms are aimed at the use of the forest as natural resource, reforestation, conservation and protection of forests, etc.

7. Law of the Russian Federation "On the Fauna" (1995). It contains environmental, legal and administrative norms, taking into account new economic relations. According to the Law, environmental and legal violations include: illegal fishing, the destruction of rare and endangered animals, etc.

8. The Law of the Russian Federation “On Production and Consumption Waste” (1998) defines legal framework management of production and consumption waste in order to prevent their harmful effects on human health and the environment.

9. The most important environmental requirements are also reflected in the Law of the Russian Federation "On the sanitary and epidemiological welfare of the population" (1999) and the Fundamentals of the legislation of the Russian Federation on health protection (1993).

Federal Law No. 26-FZ dated February 23, 1995 "On natural healing resources, health-improving areas and resorts";

Federal Law "On Specially Protected natural areas"dated March 14, 1995 (as amended on December 30, 2001) No. 33-FZ;

Federal Law "On Ecological Expertise" of November 23, 1995 (as amended on April 15, 1998) No. 174-FZ;

Federal Law "On the Use of Atomic Energy" dated November 21, 1995 (as amended on March 28, 2002) No. 170-FZ;

Federal Law "On the Continental Shelf" dated November 30, 1995 (as amended on June 30, 2003) No. 187-FZ;

Decrees and orders of the President, resolutions of the Government cover a wide range of environmental issues. An example is the Decree of the President of April 1, 1996 on the concept of the transition of the Russian Federation to sustainable development.

1. Normative acts of environmental ministries and departments are issued on a wide variety of issues of rational use and protection of the natural environment, in the form of resolutions, instructions, orders, and are considered binding on all individuals and legal entities.
2. Regulatory decisions of local administrative bodies (mayor's offices, rural and settlement authorities) supplement and specify the current regulatory legal acts on environmental protection.

The current Federal Law “On Environmental Protection” (2002) significantly expands the powers state power subjects of the Russian Federation and local governments in the field of relations related to environmental protection. In particular, the subjects of the Federation have been granted the right to develop and issue laws and other regulations in the field of environmental protection, taking into account geographical, natural, socio-economic and other features, to restrict or prohibit economic and other anti-environmental activities on their territories, etc.

population genetic structure

List of sources used

Ecology: A textbook for technical universities / Tsvetkova, Alekseev et al. Ed. L.I. Tsvetkova. - M.: Publishing House of ASV; St. Petersburg: Himizdat, 1999. - 488 p.

Korobkin V.I., Peredelsky. Ecology in questions and answers.

Korobkin V.I., Peredelsky L.V. Ecology for university students.

Www. ekolog.org

Tutoring

Need help learning a topic?

Our experts will advise or provide tutoring services on topics of interest to you.
Submit an application indicating the topic right now to find out about the possibility of obtaining a consultation.

What is a population?

Definition 1

A population is a collection of organisms of the same species, living in a given territory for a long period, having a common gene pool, as well as the ability to easily interbreed, isolated to varying degrees from other populations of this species.

Organisms of each species are represented by several populations inhabiting different territories. Between populations of the same species, there are various relationships that support the species as a whole. However, if for some reason a population becomes isolated from other populations of its own species, this can lead to the formation of a new species of living organisms. Under the influence of environmental conditions, physiological, morphological, and behavioral characteristics of organisms are formed. At the same time, the properties of organisms belonging to different populations will differ from each other the stronger, the more dissimilar the conditions of their habitat and the weaker the exchange of individuals between them.

Characteristics of populations

A population is not a random accumulation of individuals of the same species in a common area. This is a complexly organized community with its own structure, composition and complex hierarchy of connections.

The properties that characterize a population can be divided into two types:

1. biological properties - properties inherent in each organism included in the population;
2. group (emergent) properties - properties that are inherent not to individual individuals, but to the population as a whole.

In other words, the association of organisms of the same species into a population (group) is carried out on the basis of its qualitatively new, emergent properties. These properties include:

1. number;
2. population density;
3. the birth rate of organisms in a population;
4. mortality of organisms in a population.

Definition 2

Population size is the total number of individuals of the same species inhabiting a particular area.

The population size changes over time (by years, seasons, from generation to generation) and depends on external and internal factors.

Remark 1

Fluctuations in the number of individuals in a population were called by the Russian biologist S.S. Chetverikov "waves of life".

The territories (ranges) occupied by different populations can differ significantly from each other in area, so it is not always advisable to compare populations by the absolute number of individuals. In such cases, the population size is expressed as a density.

Definition 3

Population density - the ratio of the number of representatives of one species (or the corresponding biomass) and the volume or area occupied by the population (biomass) of space.

fertility- the number of newly minted individuals that appeared per unit of time as a result of reproduction. The birth rate in a population is determined primarily biological features species, as well as the average life span of an individual, the sex ratio in the population, food availability, weather conditions, and a number of other factors. There are two types of fertility:

1. maximum (absolute, or physiological) birth rate - the theoretically permissible number of individuals that can be born in ideal conditions ecological environment without any limiting factors, determined only by the physiological potentials of organisms;
2. ecological (realizable) birth rate - the number of individuals born in a certain period in specific environmental conditions.

Mortality is the number of individuals in a population that died in a given time period. It depends primarily on environmental factors and can be very high during natural disasters, during periods of adverse climatic conditions or in epidemics. Distinguish:

1. physiological mortality (death of an individual in ideal conditions as a result of physiological old age);
2. environmental mortality (death of an individual in real conditions for various reasons).

The number and density are the main parameters of the population.

population - 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 abundance and density.

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

Fertility is divided into absolute and specific. Absolute fertility is the number of new individuals that appeared per unit of time, and specific- the same number, but related to a certain number of individuals. For example, a measure of human fertility is the number of children born per 1,000 people during the year. Fertility is determined by many factors: environmental conditions, availability of food, biology of the species (rate of puberty, number of generations during the season, the ratio of males and females in the population).

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

Example: Dandelion in 10 years is able to fill the entire Earth provided that all of its seeds germinate. Willows, poplars, birches, aspens, and most weeds produce exceptionally abundant seeds. Bacteria divide every 20 minutes and within 36 hours can cover the entire planet in a continuous layer. Fertility is very high in most insect species and low in predators, large mammals.

Mortality, like the birth rate, it can be absolute (the number of individuals who 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 leading role in population dynamics.

There are three types of mortality:

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

The increased mortality in early age; characteristic of most species of plants and animals (in trees, less than 1% of seedlings survive to the age of maturity, in fish - 1-2% of fry, in insects - less than 0.5% of larvae);

High death in old age; usually observed in animals whose larval stages take place in favorable little changing conditions: soil, wood, living organisms.

Stable, growing and declining populations

The population adapts to changing environmental conditions by updating and replacing individuals, i.e. processes of birth (renewal) and decrease (death), supplemented by migration processes. In a stable population, the birth and death rates are close and balanced. They may not be constant, but the population density differs slightly from some average value. In this case, the range of the species neither increases nor decreases.

In a growing population, the birth rate exceeds the death rate. Growing populations are characterized by outbreaks of mass reproduction, especially in small animals (locust, 28-spotted potato ladybug, Colorado potato beetle, rodents, crows, sparrows; from plants - ambrosia, Sosnovsky's hogweed in the northern Komi Republic, dandelion, Himalayan sticky, partly oak Mongolian). Often, populations of large animals become growing under the conditions of a protected regime (moose in the Magadan Reserve, in Alaska, spotted deer in the Ussuri Reserve, elephants in national park Kenya) or introductions (moose in the Leningrad region, muskrat in Eastern Europe, domestic cats in separate families). When overcrowding in plants (usually coincides with the beginning of the cover density, crown canopy), differentiation of individuals in size and life condition, self-thinning of populations begins, and in animals (usually coincides with the achievement of puberty of young animals), migration begins to adjacent free areas.

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

Population structure

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

Knowledge of the population structure allows the researcher to draw conclusions about its well-being or disadvantage. For example, if there are no generative (that is, capable of producing offspring) individuals in the population and at the same time there are many old-aged (senile) individuals, then an unfavorable forecast 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 into cohorts i.e. age groups.

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

• latent period - the state of the seed;
• pre-generative period (includes the states of seedling, juvenile plant, immature plant and virginal plant);
• generative period (usually divided into three sub-periods - young, mature and old generative individuals);
• post-generative period (includes the states of a subsenile plant, a senile plant and the dying phase).

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

The sexual structure of the population

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

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

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 eggs for spermatozoa carrying the X- or Y-chromosome, the unequal ability of such spermatozoa to fertilize, and various external factors. For example, zoologists have described the effect of temperature on the secondary sex ratio in reptiles. A similar pattern is characteristic of some insects. So, in ants, fertilization is ensured at temperatures above 20 C, and at lower temperatures, unfertilized eggs are laid. Males hatch from the latter, and females from the fertilized ones.

Tertiary sex ratio is the sex ratio of adult animals.

Spatial structure populations

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 evenly spaced in space, at equal distances from each other), the type is also called uniform distribution;
• congregational, or mosaic (that is, "spotted", individuals are placed 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 only be observed in a homogeneous environment and only in species that do not show any tendency to group together. As a textbook example of uniform distribution, the distribution of the Tribolium beetle in flour is usually given.

Grouping is much more common. It is associated with the characteristics of the microenvironment or with the characteristics of the behavior of animals.

The spatial structure is of great ecological importance. First of all, a certain type of territory use allows the population to efficiently use environmental resources and reduce intraspecific competition. The efficiency of using the environment and the reduction of 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 a population is that it ensures the interaction of individuals within a population. Without a certain level of intrapopulation contacts, the population will not be able to perform both its species functions (reproduction, resettlement) and functions associated with participation in the ecosystem (participation in the cycles of substances, the creation of biological products, and so on).

Population properties: self-reproduction, variability, interaction with other populations, stability.



The concept of population in ecology

LECTURE №4

TOPIC: POPULATION ECOLOGY

PLAN:

1. The concept of a population in ecology.

2. Main characteristics of the population.

3. Structure of populations.

3.1. Spatial and ethological structure of populations.

3.2. Sex and age structure of the population.

4. Population dynamics.

4.1. survival curves.

4.2. Population growth and growth curves.

4.3. population fluctuations.

fertility- (fertility) is determined the number of new individuals that appeared per unit of time as a result of reproduction. Low fecundity is characteristic of those species that take great care of their offspring. In addition, fertility depends on the rate of maturation, the number of generations per year, the ratio of males and females in the population, the availability of food, the influence of weather conditions, and other factors.

Population mortality- This the number of individuals that died in a given period. There are three types of mortality. The first is characterized by the sameness at all ages; the second - increased death of individuals on early stages development; the third type is characterized by increased death of adult (old) individuals.

The factors of mortality are varied. These are mainly: physical conditions (low and high temperatures, heavy rainfall, drought, etc.), biological factors(lack of food, diseases, etc.) and anthropogenic (environmental pollution, deforestation, hunting, etc.).

THEORETICAL PART

The concept of a population and its main group characteristics.

population- a set of organisms of the same species, jointly inhabiting a common territory, interacting with each other and interbreeding freely. A population is an elementary form of existence of a species in nature. One species of organisms may include several, sometimes many populations, more or less isolated from each other. In populations, to varying degrees, all forms of relationships characteristic of interspecific relations are manifested, but mutualism and competition are most pronounced. There are also specific intraspecific relationships: a) between individuals of different sexes; b) between parent and child generation. The most important property of a population is the ability to reproduce.

A population as a group association of individuals has the following main characteristics:

1) number- the total number of individuals in the allocated territory; the number is not constant, because depends on many factors (reproduction rates, death of individuals as a result of old age, diseases, destruction by predators, migration); if for some reason it is impossible to determine the population size, then its density is determined;

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

3) fertility - the number of new individuals (eggs, seeds) that appeared in a population per unit of time, based on a certain number of its members (for example, the number of offspring produced by one female per year; in humans, fertility is usually expressed as the number of births per 1000 people per year); distinguish absolute And specific birth rate; the first is characterized by the total number of born individuals (for example, if in a population reindeer, numbering 16 thousand heads per year. 2,000 fawns appeared in a year, this number expresses the absolute birth rate); specific fertility is calculated as the average change in the number per individual over a certain time interval (in this example, it will be, i.e. one newborn per eight members of the population per year);

4) mortality - an indicator that reflects the number of individuals who died in a population over a certain period of time, expressed either as a percentage of total number individuals, or the average number of deaths per 1000 individuals per year; distinguish accordingly absolute And specific mortality; the value of specific fertility or specific mortality is used to compare fertility or mortality in different populations;

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

6) growth rate is the average population growth per unit of time.

The study of populations has important practical applications: for example, to control the number of pests, restore the number of wild animals, rational use of biological resources (fishing, etc.), conservation of rare species.

Population structure.

A population is characterized by a certain organization (structure). It is formed on the basis of the general biological properties of the species, under the influence of populations of other species and abiotic environmental factors.

The structure of the population has an adaptive character. different populations of the same species distinctive features characterizing the specifics of environmental conditions in their habitats.

The structure of a population can be spatial, age, sex, genetic and ecological.

Spatial structure determined by the distribution of individuals in the population area. All individuals in a population have individual and group space. There are certain radii of trophic (feeding) and reproductive activity. There are two opposite processes in the population - isolation and aggregation. Isolation factors - competition between individuals for food with its lack and direct antagonism. This leads to uniform or random distribution of individuals. Aggregation - the association of individuals into groups - although it increases competition between them, it contributes to the survival of the group as a whole due to mutual assistance. Aggregation leads to crowded distribution of individuals in a population. For example, organisms of many species prefer to stay in flocks (birds) or herds (mammals).

Age structure population is determined by the number and ratio of individuals of different ages, reflects the intensity of reproduction, mortality rate, the speed of generational change. In a stable population, groups of different ages are approximately in the same ratio, the birth rate is equal to the death rate, and the population size remains almost unchanged. The growing population is represented mainly by young individuals, here the birth rate exceeds the death rate. If the population is dominated by senile individuals, then its number decreases.

Sex structure- the number and ratio of males and females of the population. Genetic two-factor chromosomal sex determination provides an equal number of sexes. But in some cases, the sex ratio is determined by hormonal factors that act after fertilization, as well as environmental ones. As a result, the sex ratio in the population fluctuates over the years, deviating from 1:1.

genetic structure is determined by the variability and diversity of genotypes, the frequency of variations of individual genes, as well as the division of the population into groups of genetically close individuals, between which there is a constant exchange. The diversity of genotypes depends on the size of the population and external factors affecting its structure. In small, isolated and stable populations, the frequency of inbreeding naturally increases, which reduces genetic diversity and increases the threat of extinction.

ecological structure- this is the subdivision of a population into groups of individuals that interact differently with environmental factors. Groupings are revealed by nutrition (individuals of different sex and age have different food preferences), by orientation behavior, and by physical activity. Often there is a distribution of functions when hunting for prey, when caring for offspring. All populations are also characterized by phenological differentiation (different dates for the beginning and end of seasonal cycles of development and behavior: hibernation, sexual activity, molting, flowering, fruiting, leaf fall, etc.).

Population dynamics.

A population cannot exist without constant changes, due to which it adapts to changing environmental conditions. Changes in the number of organisms over time are called dynamics populations. The concept of population growth is necessary to understand their ability to restore numbers, as well as to understand some of the properties of dynamics.

Any population is theoretically capable of unlimited growth in numbers, if it is not limited by factors external environment. In this case, the population growth rate will depend only on the magnitude biotic potential (b.p.), characteristic of the species. B.P. reflects the theoretical maximum of offspring from one pair or individual per unit of time. B.P. is expressed by the coefficient r and calculated according to the following formula:

where ΔN - population growth;

Δt is the period of time for which there is an increase in ΔN;

N 0 - initial population size.

In nature, the B.P. of a population is never fully realized. Usually, its value is added as the difference between births and deaths in populations:

where: in - the number of births,

d - the number of dead individuals in the population for the same period of time.

Population growth and growth curves. If the birth rate in a population exceeds the death rate, then the population will grow (if the change due to migration is negligible). To understand the patterns of population growth, it is useful to first consider a model that describes the growth of a bacterial population after inoculation on a fresh culture medium. In this new and favorable environment, conditions for population growth are optimal and exponential growth (J-shaped) is observed. This growth curve is called exponential, or logarithmic (Fig. 1).

Fig.2. Logistic population growth curve (S - shaped)

Eventually, a point is reached where, for several reasons, including diminishing food resources and the accumulation of toxic waste products of metabolism, exponential growth becomes impossible. It begins to slow down so that the growth curve takes on a sigmoid (S-shaped) shape and is called logistic(Fig. 2).

Sigmoid and J-shaped curves are two patterns of population growth. It is assumed that all organisms are very similar to each other, have an equal ability to reproduce and an equal probability of dying, so that the population growth rate in the exponential phase depends only on its size and is not limited by environmental conditions, which remain constant.

In nature after the exponential phase further development population follows a logistic model, while the population growth rate decreases linearly as the population grows up to zero at a certain value of K. The value of K is called biological capacity of the medium(the degree of ability of the natural or natural-anthropogenic environment to ensure the normal functioning of a certain number of organisms without a noticeable violation of the environment itself).

A survival curve can be obtained by starting with a population of newborns and then plotting the number of survivors over time. On the vertical axis, either the absolute number of surviving individuals or their percentage of the original population is usually laid:

Each species has a characteristic survival curve, the shape of which depends in part on the mortality of immature individuals. Typical examples are shown in Figure 3.

100

Fig.3. Three Types of Survival Curves

Most animals and plants are subject to senescence, which manifests itself in a decrease in vitality with age after a period of maturity. As soon as aging begins, the probability of death in a certain period of time increases. The immediate causes of death may be different, but they are based on a decrease in the body's resistance to the action of adverse factors (for example, diseases). Curve A in Fig. 2 is very close to the ideal survival curve for a population in which aging is the main factor influencing mortality. An example would be the human population in modern developed country with a high level of medical care and rational nutrition, where most people live to old age. A curve similar to curve A is also characteristic of annual cultivated plants, when they age simultaneously in a given field.

The Type B curve is characteristic of populations of organisms with high early mortality, such as mountain sheep, or a human population in a country where famine and disease are widespread. A smooth curve of type B can be obtained if mortality is constant throughout the life of the organisms (50% per unit of time). This can be when chance becomes the main factor determining mortality, and individuals die before noticeable aging begins. A similar curve is typical for populations of some animals (for example, hydra) that are not particularly endangered at an early age. Most invertebrates and plants also exhibit this type of curve, but the high juvenile mortality causes the initial part of the curve to descend even more steeply.

There are small intraspecific differences in survival curves. They can be due to various reasons and are often associated with gender. In humans, for example, women live slightly longer than men, although the exact reasons for this are unknown.

Drawing survival curves for various kinds, it is possible to determine mortality for individuals of different ages and, thus, to find out at what age a given species is most vulnerable. By establishing the causes of death at this age, one can understand how the size of the population is regulated.

Similar information.