Definition of population main characteristics. Characterization of populations. Spatial structure of the population

The concept of a population. Types of populations

Population(populus - from lat. people. population) is one of the central concepts in biology and denotes a collection of individuals of one species, which has a common gene pool and has a common territory. It is the first supraorganic biological system. From an environmental perspective, a clear definition of a population has not yet been developed. The most recognized was the interpretation of S.S. Schwartz, a population - a group of individuals, which is a form of existence of a species and is able to independently develop indefinitely.

The main property of populations, like other biological systems, is that they are in constant motion, constantly changing. This is reflected in all parameters: productivity, stability, structure, distribution in space. Specific genetic and environmental traits are characteristic of populations, reflecting the ability of systems to maintain their existence in constantly changing conditions: growth, development, and sustainability. The science that combines genetic, environmental, and evolutionary approaches to studying populations is known as population biology.

EXAMPLES One of several schools of fish of the same species in the lake; microgroups of the Keyske lily of the valley in the white birch forest, growing at the base of trees and in open places; curtains of trees of one species (Mongolian oak, larch, etc.), separated by meadows, curtains of other trees or shrubs, or swamps.

Ecological population -  totality of elementary populations, intraspecific groups confined to specific biocenoses. Plants of the same species in cenosis are called coenopopulation. The exchange of genetic information between them occurs quite often.

EXAMPLES Fish of the same species in all schools of a common reservoir; stands in monodominant forests, representing one group of forest types: grassy, \u200b\u200blichen or sphagnum larch (Magadan region, north of the Khabarovsk Territory); stands in sedge (dry) and mixed (wet) oak forests (Primorsky Territory, Amur Region); protein populations in pine, spruce-fir and broad-leaved forests of one region.

Geographic population - a set of ecological populations that populate geographically similar areas. Geographic populations exist autonomously, their ranges are relatively isolated, gene exchange is rare - in animals and birds - during migrations, in plants - when pollen, seeds and fruits are spread. At this level, the formation of geographical races, varieties, subtypes are distinguished.

EXAMPLES The geographical races of Daurian larch (Larix dahurica) are known: western (to the west of Lena (L. dahurica ssp. Dahurica) and eastern (east of Lena, distinguished in L. dahurica ssp. Cajanderi), northern and southern races of Kuril larch. the allocation by MA Shemberg (1986) of stone birch of two subspecies: Erman birch (Betula ermanii) and woolly (B. lanata). In the lower reaches of the Yama River, there is a focus of ordinary spruce (Picea obovata), which is located to the east from a continuous array of spruce forests per 1000 km, to the north - 500 km .. Zoologists distinguishes the tundra and steppe populations from the narrow-cranked vole (Microtis gregalis) The species "common protein" has about 20 geographical populations, or subspecies.

Key characteristics of populations

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 dynamicsand 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 rateIs 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 of 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.

Populations and their environmental characteristics.

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

Ecological characteristics of populations  - This is a list of features that describe the interaction of populations with a set of environmental factors of a particular habitat.

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

2. Population structure.

Within the population, it is possible to distinguish groups that determine its characteristic structure.

Population structure - dividing the population into groups of individuals that differ in certain properties (size, gender, location, behavior, etc.).

Distinguish the following types of population structure:

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

2) age structure  - distribution of individuals by age groups;

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

4) ethological structure  - a system of relationships between individuals that manifests itself in their behavior; Thus, the main forms of organization of animal populations are a single lifestyle (for example, most spiders, mallard duck) and group lifestyle in the form of families (truths of lions), colonies (in wild rabbits, coastal swallows), flocks (in locusts, wolves ), herds (in ungulates, cetaceans).

3.Population waves .

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

There are population waves seasonal and non-seasonal:

Seasonalpopulation waves - due to the peculiarities of life cycles or seasonal changes in climatic factors;

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

A population by itself can maintain its population for unlimited time. At the level of the population, there are processes of self-regulation that bring the density of the population into line with the capacity of the environment and are manifested in the form of waves of life.

The main mechanisms of population regulation are:

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

2) regulation of settlement (protein migration);

3) regulation of social behavior (in public insects, individual female uterus and males participate in breeding, the number of which is regulated in the process of reproduction);

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

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

Due to long-term adaptation to living conditions, populations have developed mechanisms to avoid unlimited growth in numbers and help maintain population density at a relatively constant level.

4.Population homeostasis - ϶ᴛᴏ maintaining the population at a certain level optimal for a given habitat. Abiotic factors as well as interspecific and intraspecific relationships affect the homeostasis of a population. 5. Ecosystems, their structure and properties.

Ecosystem-the totality of organisms of different species and their habitats associated with the exchange of matter, energy and information. A home aquarium, a lake on the outskirts of the village, a steppe beam, a forest, a spacecraft cabin, our whole planet are all ecosystems of a single biosphere. The concept of "ecosystem" was proposed in 1935 by A. Tesli. The functioning of the ecosystem is ensured by the “internal” biological circulation of substances between abiotic and biotic parts. Ecosystems are open biosystems, and in this regard, for existence in time, “external” flows of energy, matter and information are necessary as part of the general geological cycle.

Close to ecosystems is biogeocenosis.

Biogeocenosisit is a definite territory with homogeneous living conditions, populated by interconnected populations of different species, united by a circle through the gates of substances and the flow of energy.The concept of biogeocenosis was introduced by V.M.Sukachov (1940). The basis of the vast majority of biogeocenoses are photosynthetic organisms that form plant groups. Biogeocenosis, in contrast to the ecosystem, is a specific, territorial concept, because it occupies a limited area with uniform living conditions and with the corresponding phytocenosis (plant groups).

In the ecosystem emit biotic and abiotic parts. The biotic part of the ecosystem is a set of interconnected living organisms that form a biocenosis. Biocenosis is a grouping of interconnected populations of organisms of different species inhabiting a site with homogeneous living conditions. This concept was proposed by the German hydrobiologist K. Myobius. The basis of biocenoses is phytocenosis(plant groups) with which zoocenoses (animal groups) and microbiocenoses (a group of microorganisms) are associated. Biocenoses exist in a certain area of \u200b\u200bthe environment, which is commonly called biotope.

  The biotic part of the ecosystem  make up various environmentalgroups of organisms, interconnected by spatial and trophic connections - producers, consumers and reducers.

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

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

Part abiotic parts  Biogeocenosis includes the following components:

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

Organic matter-connections that connect the abiotic and biotic parts of the ecosystem;

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

Main properties  Ecosystems are: integrity, self-reproduction, sustainability, self-regulation, etc. Interconnections between populations in ecosystems . The composition and structure of groups, their stability and change depends on complex relationships between populations of different species. Allocate the following types of connections   between individual populations of different species in ecosystems:

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

Trophic  - these are nutrition links (predator-prey);

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

Antibiotic relationship  (predation, competition, eating) - each of the interacting populations of different species is negatively affected by the other;

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

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

Control of knowledge and skills:

1) What is a population structure?

2) What are the different types of population structure?

3) How is the population size regulated?

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

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

Homework: retelling of the synopsis28 §28.29, (30-33.47) prepare reports, Lek. 25.

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

A population is a historically developed natural totality of individuals of a given species, interconnected by certain relationships and adaptation to life in a particular area. For the first time this term was used by W. Johansen in 1903. The population has a common gene pool and occupies a certain territory. The main property of a population is its continuous change, movement, dynamics, this greatly affects the structural and functional organization, productivity, biological diversity and stability of the system.

Population  (from Latin: “populus” - people) is a collection of freely crossing individuals of the same species that exists for a long time and occupies a certain part of the range relatively separated from other populations of the same species. A population is an elementary structure of a species in the form of which a species exists in nature.

Populations as groups of individuals possess a number of specific indicators that are not characteristic of each individual individual. Quantitative and qualitative characteristics of populations are determined by external factors (mass / extent \u003d density, mass / dispersion \u003d abundance, distribution, ecological structure). At the same time, two groups of quantitative indicators are distinguished - static and dynamic.

The state of the population at a given time is characterized by static indicators. These include abundance, density, age composition.

Population size - this is the number of individuals of a given species in a population in a given territory. The population size is not constant and varies in one or another limit, it depends on the ratio of the intensity of reproduction and mortality.

Population density- this is the number of people per unit area or volume. At different stages of the life cycle, density can fluctuate significantly. This is directly related to two other indicators of the population: fertility and mortality.

Dynamic indicators  populations include fertility, mortality, growth, population growth rate.

Birth rate  - this is the ability of a population to increase in number, regardless of whether it occurs by laying eggs, by dividing, budding, germinating from a seed or otherwise. The most indicative is the specific birth rate, defined as the number of individuals that appeared in the unit of time per individual in the population (in demography, the calculation is per woman of reproductive age). Real fertility largely depends on environmental factors, therefore it is always less than the maximum birth rate, which theoretically means the maximum birth rate, determined only by the physiology of individuals with optimal values \u200b\u200bof all environmental factors.

Fertility is usually expressed as the rate determined by dividing the number of newly formed individuals over a certain period of time (d \u003d Nn / dt is the absolute birth rate) or the number of new individuals per unit of the population (dNn / Ndt is a specific, specific birth rate), where N is the population size or only a part capable of reproduction. For example, for higher organisms, fertility is expressed per female, and for a human population, per 1000 people.

Fertility can be zero or positive, but never negative.

Mortalitycharacterizes the death of individuals in a population and is expressed by the number of individuals. Mortality also depends on environmental factors and is usually much higher than the minimum mortality under ideal environmental conditions, which is determined by the physiology of a given species of organisms — even under ideal conditions individuals will die of old age.

Distinguish specific mortality - the number of deaths in relation to the number of individuals that make up the population; ecological, or realizable, mortality - the death of individuals in specific environmental conditions (the value is variable, varies depending on the state of the environment and the state of the population).

There is a certain minimum value characterizing the death of individuals under ideal conditions when the population is not affected by limiting factors. Under these conditions, the maximum lifespan of individuals is equal to their physiological life, which is on average higher than the ecological lifespan.

An ecosystem is the main functional unit of living nature, including organisms and an abiotic environment, with each of the parts influencing the other and both are necessary to maintain life in the form in which it exists on Earth. The dual nature of this complex was emphasized by V.N. Sukachev in the doctrine of biogeocenosis.

The biotic part of the ecosystem necessarily includes two main components: 1) an autotrophic component, which is characterized by the fixation of light energy, the use of simple inorganic substances, the construction of complex substances; 2) a heterotrophic component, which is characterized by the utilization, rearrangement and decomposition of complex organic substances. Very often, the organisms representing these two components are separated in space; they are arranged in tiers, one above the other. Autotrophic metabolism most intensively occurs in the upper tier - the “green belt”, i.e. where light energy is most available, and heterotrophic metabolism prevails at the bottom, in the soils and sediments of the “brown belt”, in which organic matter accumulates.

As a result of energy dissipation in food chains and due to such a factor as the dependence of metabolism on the size of individuals, each community acquires a certain trophic structure, which can be expressed either by the number of individuals at each trophic level, or by a standing crop, or by the amount of energy fixed per unit area per unit of time at each subsequent trophic level. Graphically, this can be represented in the form of a pyramid, the basis of which is the first trophic level, and the subsequent ones form the floors and the top of the pyramid (3-figure). There are three main types of ecological pyramids - pyramids of numbers, biomass and energy.

When studying the biotic structure of an ecosystem, nutritional relationships between organisms are one of the most important indicators of the state of populations. You can trace the countless paths of movement of matter in the ecosystem, in which one organism is eaten by another, and the other by the third, etc.

The food chain is the path of movement of a substance (energy source and building material) in an ecosystem from one organism to another. The food chain is a sequence of organisms in which each of them eats or decomposes the other. It represents the path of a unidirectional stream moving through living organisms, absorbed during photosynthesis, of a small part of the highly efficient solar energy received on Earth. Ultimately, this chain returns to the surrounding natural environment in the form of thermal energy. It also moves nutrients from producers to consumers and then to reducers, and then back to producers.

Thus, it consists of three main links: producers, consumers and reducers. Food chains that start with photosynthetic organisms are called eating chains (grazing), and chains starting with dead plant debris, carcasses and animal excrement are called detrital chains.

The location of each link in the power circuit is called trophic levelsthey are characterized by different intensities of the flow of substances and energy. The first trophic level is always made up by producers, herbivorous consumers belong to the second trophic level, carnivores living due to herbivorous forms to the third, consumers of other carnivores to the fourth, etc. population ecosystem indicator

Detritophages can be at the second and higher trophic level.

There are usually 3-4 trophic levels in an ecosystem. This is because a significant part of the consumed food is spent on energy (90-99%), so the mass of each trophic level is less than the previous one. Relatively little is used to form the body of the body (1--10%).

In nature, food chains are rarely isolated from each other. More often, representatives of one species (herbivorous) eat several types of plants, and they themselves serve as food for several species of predators.

Thus, food chains are not isolated from one another, but are closely intertwined. They make up the so-called food networks. The principle of food network formation is as follows. Each producer has not one, but several consumers. In turn, consumers, among which polyphages predominate, use not one, but several power sources (1-2 figures).

The food web is a complex network of food relationships.

Despite the diversity of food chains, they have common patterns: from green plants to primary consumers, from them to secondary consumers, etc., then to detritophages. Detritophages are always in last place; they close the food chain.

At each stage of the transfer of matter and energy through the food chain, approximately 90% of the energy is lost and only about 1/10 of its part goes to the next consumer. The indicated ratio in the transfer of energy in the food bonds of organisms is called the Lindemann principle.

The concept of a population in ecology

LECTURE №4

TOPIC: POPULATION ECOLOGY

PLAN:

1. The concept of a population in ecology.

2. The main characteristics of the population.

3. The structure of populations.

3.1. Spatial and ethological structure of populations.

3.2. Sexual and age structure of the population.

4. The dynamics of populations.

4.1. Survival curves.

4.2. Population growth and growth curves.

4.3. Fluctuations in population size.

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

Population mortality  - this is  the number of individuals killed over a given period. There are three types of mortality. The first is characterized by uniformity at all ages; the second is increased death of individuals in the early stages of development; the third type is characterized by increased death of adults (old) individuals.

Mortality factors are diverse. This is mainly: physical conditions (low and high temperatures, rainfall, drought, etc.), biological factors (lack of food, disease, etc.) and anthropogenic (environmental pollution, deforestation, hunting, etc.).

What is a population?

Definition 1

A population is a collection of organisms of the same species, which have been living in a given area for a long period, having a common gene pool, and also the ability to easily interbreed, to various degrees, isolated 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 the population falls into isolation from other populations of its species, this may lead to the formation of a new species of living organisms. Under the influence of environmental conditions, physiological, morphological, behavioral characteristics of organisms are formed. At the same time, the properties of organisms belonging to different populations will differ among themselves the stronger, the more dissimilar their living conditions and the weaker the exchange of individuals between them.

  Characterization of populations

A population is not an accidental accumulation of individuals of the same species on the common territory. This is a complexly organized community with its own structure, composition and complex hierarchy of relations.

The properties characterizing the population can be divided into two types:

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

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

1. strength
2. population density;
3. fertility of organisms in a population;
4. mortality of organisms in a population.

Definition 2

Population - the total number of individuals of the same species inhabiting a specific territory.

The population size varies over time (by year, season, from generation to generation) and depends on external and internal factors.

Remark 1

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

Territories occupied by different populations (ranges) can vary significantly in area, so comparing populations by the absolute number of individuals is not always advisable. In such cases, the population is expressed as density.

Definition 3

Population density is 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.

Birth rate - the number of newly minted individuals that appeared per unit time due to reproduction. Fertility in a population is determined primarily by the biological characteristics of the species, as well as the average life of an individual, the ratio of sexes in a population, food availability, weather conditions, and a number of other factors. There are two types of fertility:

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

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

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