Cohabitation of populations of different species in a certain territory. Types of relationships between organisms
Abstract on ecology
All living organisms in nature necessarily exist in the form of populations.
Population (from lat. - population) - this is a collection of individuals of the same species that inhabit a certain space for a long time, having common gene pool, opportunity freely interbreed and more or less isolated from other populationsthis kind. A population is the elementary form of existence of a species in nature. Populations evolve and are the units of species evolution and speciation. Possessing all the characteristics of a biological system, a population, nevertheless, is a collection of organisms, as if isolated from the natural system, since in nature, individuals of one species always coexist with individuals of other species. The main characteristics of a population are size, density, fertility, mortality, age composition, distribution over the occupied territory and type of growth.
Population size different from different types and cannot be below certain limits below which population extinction occurs.
Population density determined by the number of individuals per unit of occupied area or volume. Each species has a certain density, deviations from which also negatively affect the life of individuals.
Fertility and mortality – this is the number of born and died individuals over a certain period. These indicators are largely determined by the biology of the species, food supply, and climatic conditions.
Age composition is of great importance for the existence of the population. Under favorable conditions, all age groups are present in the population and their ratio is maintained at a more or less stable level. In rapidly growing populations, intensively reproducing young individuals dominate, while in declining populations, old individuals, no longer capable of intensive reproduction, dominate.
The nature of the distribution of individuals across the territory may be uniform, crowded or random.
Changes in the number and density of populations have characteristics for each species and are determined by both the state environment, and the patterns of relationships between organisms, i.e., a set of abiotic and biotic factors. The number and density of populations does not remain constant and fluctuates within more or less wide limits. The importance of patterns of dynamics of population numbers and density is important to predict possible adverse events.
The ratio of birth and death rates in a population determines the balance of the population. If the birth rate is higher than the death rate, then the population grows numerically, and vice versa. However, in practice, for ecologists it is not the quantitative changes populations, and their speed.
Under fertility ( R ) understand the numerically expressed ability of a population to increase. Fertility can only be a positive or zero value, but cannot be a negative value. However, the rate of population growth can be any. Mortality ( WITH ) populations are expressed by the number of individuals that died over a certain period of time.
The proportion of individuals in a population that survive to a certain point in time or to the age of reproduction is called population survival.
The theoretical rate of natural population growth in an environment unrestricted by any factors is characterized by an exponential growth law:
Where N 0 And Nt – initial and determined at the moment t – number of individuals in the population; r = R – C – population growth.
It is clear that the ideal law cannot be implemented in real conditions and unlimited population growth is impossible. There are always some values of extremely low ( M ) and extremely high ( K ) population size or density. In practice, two options for population dynamics are possible.
The first option is that the population size stabilizes over time and its dynamics are characterized by the so-called logistic curve, expressed by the equation:
Attitude (K – M)/K sometimes called “environmental resistance,” which is understood as a set of factors that prevent unlimited population growth.
The second option for population dynamics is that after reaching the upper limit of numbers ( TO ) mass death of individuals occurs, as a result, the population size returns to a certain lower limit, after which the population growth can begin again.
Fluctuations in population numbers can be periodic or non-periodic. Cyclical dynamics of population numbers are typical for more or less large organisms, and the logistic type of growth is characteristic only for small organisms or for organisms with very simple life cycles. Any fluctuations in population size are the result of changes in the environment, and can also arise as a result of intra-population and inter-population relationships.
Any set of populations of different species of organisms inhabiting a certain territory with homogeneous abiotic properties ( biotope) , is biotic community or biocenosis . For example, we can talk about the biocenosis of a tree trunk, the biocenosis of the taiga, or the biocenosis of the ocean.
Biocenosis is a supra-organismal system in which individual species, populations and groups of species can be replaced by others, respectively, without much damage to the community, and the system itself exists by balancing the forces of antagonism between species. The stability of the biotic community is determined by the quantitative regulation of the numbers of some species by others, and its size depends on external reasons– on the size of the territory with homogeneous abiotic properties, i.e. biotope.
Biocenosis is a higher level of organization than the population that is its integral part. The biocenosis has a complex internal structure, from which species and spatial structures are distinguished.
All biotic communities can be divided into main communities, which are characterized by large sizes and completeness of organization and do not depend on neighboring communities, and small communities, to one degree or another, dependent on neighboring communities. Communities have a certain structure connections, functional and compositional unity, which provides the possibility of coexistence various types organisms.
The species structure of the biocenosis is characterized by species diversity and the quantitative ratio of species, depending on a number of factors. For the existence of a community, not only the size of the number of organisms is important, but even more important is species diversity, which is the basis biological diversity in living nature. The richness of the species composition of biocenoses is determined by the number of species. Natural biocenoses are considered poor if they contain tens and hundreds of species of plants and animals, rich - several thousand or tens of thousands of species. Species diversity is interrelated with the diversity of habitat conditions. The more organisms find suitable conditions for themselves in a given biotope. environmental requirements, the more species will settle in it.
The most favorable conditions for the existence of many species are characteristic of transition zones between communities that are called ecotones , and the trend is increasing here species diversity called the edge effect. The ecotone is rich in species, primarily because they come here from all border communities, but, in addition, it can contain its own characteristic species, which do not exist in these communities. A striking example This is the forest “edge”, on which the vegetation is lush and richer, nesting is significant more birds, more insects, etc. than in the depths of the forest.
Species that predominate in numbers are called dominant, or simply - dominants of this community. But even among them there are those without which other species cannot exist. They are called edifiers (Latin – “builders”). They determine the microenvironment (microclimate) of the entire community and their removal threatens the complete destruction of the biocenosis. As a rule, edificators are plants - spruce, pine, cedar, feather grass, and only occasionally - animals.
Relationships with other organisms of the same species play important role in the life of plants or animals. Such relationships develop in small groups, which in biology are called populations. Population refers to a collection of individuals of the same species that share a common gene pool and a common territory. Ecologists define it as the first supraorganism biological system. A more precise definition of the population was given by Russian academician Stanislav Semenovich Schwartz. He determined that a population is a grouping of individuals, which is a form of existence of a species and is capable of independently developing indefinitely for a long time. The term "population" was introduced by Wilhelm Ludwig Johansen in 1903.
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“37.Population structure. Types of interaction of different types"
Relationships with other organisms of their own species play an important role in the life of plants or animals. Such relationships develop
in small groups that
in biology are called populations.
![](https://i2.wp.com/arhivurokov.ru/multiurok/html/2017/02/06/s_58986b7e0eea6/img_s549046_0_1.jpg)
Population denotes a collection of individuals of the same species that has a common gene pool and a common territory.
![](https://i0.wp.com/arhivurokov.ru/multiurok/html/2017/02/06/s_58986b7e0eea6/img_s549046_0_2.jpg)
A more precise definition of the population was given by Russian academician Stanislav Semyonovich Schwartz. He determined that population- a grouping of individuals, which is a form of existence of a species and is capable of independently developing for an indefinitely long time.
![](https://i2.wp.com/arhivurokov.ru/multiurok/html/2017/02/06/s_58986b7e0eea6/img_s549046_0_3.jpg)
The term "population" was introduced Wilhelm Ludwig Johansen
Population is a biological system
and tends to constantly change.
Wilhelm Ludwig Johansen
1877–1939 gg.
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Each population is characterized by certain genetic And environmental signs. The science that combines genetic, ecological, and evolutionary approaches to the study of populations is called population biology .
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Population types
Geographical
Elementary
Ecological
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Elementary, or local population- this is a collection of individuals of the same species, which occupies a small area of the same territory according to the conditions. Genetic information is constantly exchanged between these individuals.
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Lungwort
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Ecological population constitutes the totality elementary populations. This intraspecific groups, which are adapted
to the conditions of a specific ecological system.
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Geographic population represents a collection of ecological populations that inhabit geographically similar areas. Geographic populations exist autonomously, their habitats are relatively isolated, and gene exchange occurs rarely.
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This is how geographical populations were formed in nature Daurian larch And Kuril larch .
Kuril larch
Dahurian larch
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The birch, which spread and moved away from its original habitat, formed two geographic populations. Now known birch warty And woolly birch .
Birch warty
Woolly birch
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Common squirrel spread over a very large area. There are currently about 20 geographic populations of squirrels.
The main characteristics of populations are number And density .
Common squirrel
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Number population is determined by the total number of individuals
in a certain area.
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Density is the number of individuals per unit area. Changes in population size and density depend on
from fertility, mortality and migration.
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A dandelion can spread throughout the planet in 10 years if all its seeds germinate. Bacteria multiply quickly, and in 3 days they can cover the entire planet with a continuous layer. High fertility is observed in many insect species.
Dandelion
Bacteria
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Mortality characterizes the rate of population decline. Causes of mortality are illness, old age, predators, lack of food.
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Population structures
Spatial
Demographic
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Under demographic structure populations understand it sexual And age composition .
Sex ratio
in populations is determined
in some species living conditions.
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In aphids, for example, in the summer generations replace each other, which consist only
from females. Under unfavorable conditions, males appear.
In a number of gastropods, polychaete worms, crustacean individuals change sex with age.
Snail
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Spatial structure population reflects the pattern of distribution of individuals
in space.
Organisms different populations settle in space
differently.
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For example, stinging nettle
within its range it occurs in moist, shady places
with fertile soils, forms thickets in floodplains of rivers, streams, around lakes,
along the edges of the swamps. Cabbage whites live where cabbage is grown -
in gardens and fields.
stinging nettle
Belyanka
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European mole
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This uniform distribution occurs
in nature is rare and most often caused by acute intraspecific competition, which is observed
at predatory fish and in sticklebacks
with their territorial instinct and purely individual character.
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Also spatial distribution may be random. Random distribution of individuals occurs only in a homogeneous environment and only
in species that do not strive
to create groups.
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WITH pine forest trees initially settle in groups, and then
their placement becomes uniform. Group distribution provides higher stability in relation to
to unfavorable conditions compared to an individual.
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Animals that lead an active lifestyle are actively distributed, which leads to intensive mixing of populations and blurring of boundaries between them. Populations of different species that live in the same territory enter
into various relationships with each other.
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But more often than not, organisms of different populations in the same territory interact with each other
with a friend in a competitive fight. Competition is heating up for the same resources. For example, plants fight for light.
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Symbiotic relationships can also arise between populations. These include adaptations that are beneficial to everyone and the close coexistence of organisms.
Euglena green
Termites
on the body of a rhinoceros, and
their takeoff is a signal of danger for the rhinoceros.
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There are relationships in which one species receives an advantage, benefit,
without causing harm to others,
no benefit. This is how populations of hyenas, vultures, and lions adapted to each other. Hyenas pick up the remains of prey left uneaten by the lions, then the vultures begin the meal.
Hyena
Vultures
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The concept of “population” should be associated in our minds not with a frozen museum collection, but with a busy airport, where some people are constantly arriving, while others are leaving.
A.M. Gilyarov
Experimental material accumulated in ecology by the first quarter of the twentieth century led to the formation of a new approach to its analysis. Gradually, ecologists, along with the study of morphology, physiology and behavior individual organisms and types(autechology), moved on to studying the properties groups of cohabiting individuals of one species or another, marking the beginning of the development of a new direction in ecology.
A collection of individuals of the same species living for a long time in a certain territory is called a population. The branch of ecology that studies population dynamics described by a number of characteristics is called demecology .
Although the term "population" has received wide use in the first half of the 20th century, the roots of this concept are found in ancient literary sources. Already in the works of Aristotle one can find indications of connections between organisms, cohabitation of animals and forms of groupings. He identified groups of nomadic and sedentary animals, leading a solitary and group lifestyle. The "Father of Botany" Theophrastus described natural plant communities as a collection of species confined to certain landscapes. Without dwelling on the history of the development of the concept of population, we note that this term took root in ecology rather slowly, and until 1930 (the publication of the book by K. Friederichs, translated into Russian in 1932 under the title " Ecological fundamentals applied zoology and entomology") was almost never used in the scientific literature. Until that time, the idea of a population as a special phenomenon organic world was missing. The clarification of the concept of “population” is associated with the rapid development in the 20th century. biological sciences such as genetics and ecology.
4.1. DEFINITION OF POPULATION
The term “population” was borrowed from demography, where it meant people, population (from the Latin populus). A population is understood as any collection of individuals of the same species living for a long time in a certain territory, freely interbreeding with each other and producing fertile offspring.
Many biologists have devoted themselves to the study of certain populations of animals, plants, and microorganisms. Each of them knew well what he understood by the word “population,” but the very definition of population differs among many researchers. This is connected primarily and mainly with the tasks that each researcher set for himself. You can study the population of the Colorado potato beetle inhabiting a single potato leaf, or study the totality of all Colorado potato beetles on a potato bush as a whole, or study these insects throughout the entire potato field.
There are many definitions of population, which indicates the ambiguity of the concept of this term by different biologists and ecologists. Let's list a few of them. First of all, one of the classic definitions of S.S. Schwartz is an animal ecologist. In his definition population is an elementary grouping of individuals of the same species, occupying a certain territory and possessing all necessary conditions to maintain stability for a long time in changing environmental conditions. It is easy to see that he defined the population from evolutionary-ecological concepts.
From the perspective of modern genetics population is a collection of individuals of the same species that have a common gene pool and inhabit a certain space, with relatively homogeneous conditions a habitat(N.F. Reimers).
The ecological aspect of population biology, in contrast to the genetic-evolutionary one, is aimed at studying the “everyday” life of a population as a form of existence of a species in specific ecosystems. From these positions, the definition of population given by I.S. Shilov is characteristic: a population is a group of individuals of the same species inhabiting a certain territory and characterized by a common morphobiological type, specificity of the gene pool and a system of stable functional relationships.
Thus, the concept of a population of a microbiologist studying bacteria may differ from that of a botanist studying meadow or forest vegetation, or a zoologist studying the natural groupings of lions, the migration of birds, or colonies of attached animals of the ocean. Often, ecologists do not think about defining a population at all, but use this term to designate any collection of individuals of the same species inhabiting some more or less homogeneous territory or contained in laboratory conditions. For example, for geneticists, the community of Drosophila flies living in a test tube will be the same population as the strains of various bacteria in Petri dishes for microbiologists. And yet, despite the discrepancies, close attention should be paid to the definition of the concept of “population” and its basic properties.
In the most general view a population can be defined as a group of organisms of one specific species that live together in a separate area and have common properties. Based on this definition, a population can be called all blackbirds living in some forest area, all daphnia inhabiting a separate pond or puddle, all flour beetles living in one jar. TO general properties, uniting all these organisms in special system, first of all, one should include the property of general relatedness (more specifically, the genetic relatedness of the organisms that make up the population) and the habitat of species in similar conditions.
For geneticists, such a definition of a population as any group of organisms of the same species in a certain territory is no longer enough. Indeed, in this case, the population is both a colony of mice in a cage and a species population of entire landscape areas, for example squirrels in Eurasia. Therefore, along with the development of the concept of population, ecologists increasingly take into account a certain internal structure of the population, its heterogeneity, and the dissimilarity of individuals of the same species. The population appeared as a complex evolutionary formation with its own internal structure and certain laws of organization and functioning.
An ecologist studying individual populations is not satisfied with the simplified definition that would satisfy an ecologist specializing in the study of ecosystems. Firstly, there are often cases when, during their life, individuals of a species move from one ecosystem to another (for example, in dragonflies, larvae develop in water). Secondly, situations are possible when several genetically isolated populations live in a large area occupied by one ecosystem, each of which may have its own environmental features. Therefore, when studying individual populations, it is necessary to closely monitor all life stages of the species being studied, regardless of what ecosystems they are part of.
In some cases, an ecologist treats the studied set of individuals as a population, while a geneticist identifies within it groups of individuals that are not related to each other and do not exchange genes with each other. Thus, among daphnia of the same species inhabiting small pond, geneticists have discovered several different parthenogenetically reproducing families. An ecologist, when solving certain problems, can neglect these genetic differences.
The most important characteristic of a population is the area it occupies. general territory. But within a population there may be groups that are more or less isolated for various reasons. Therefore, it is difficult to give an exhaustive definition of the population due to the blurred boundaries between individual groups of individuals.
Among the many species of living organisms, there are those that stay in the same territory for a long time, maintaining a more or less constant number. Other species are characterized by strong fluctuations in numbers, often accompanied by significant changes in the area of the occupied territory. A classic example is some locusts, which form a migratory “gregarious” phase and give real bursts of numbers. For example, during the formation of the “gregarious” phase, the red locust living in Africa increases its distribution area by thousands of times compared to the area where it lives permanently. Thus, in 1962, in the south of Morocco, locusts destroyed 7 thousand tons of oranges in five days (60 tons per hour). This figure exceeds the annual consumption of citrus fruits in a country like France.
In 125 BC, locusts destroyed all the wheat and barley crops in the Roman provinces of Cyrenaica and Numidia (in North Africa), and the population of these countries was 800 thousand people! - died of hunger.
Phenomena when swarms of locusts cover air space over an area of 5-12 square kilometers, are not at all rare. In such a flock there are from 700 million to 2 billion insects, and their total weight is about 3 thousand tons (2.5 tons per hectare). Moreover, there are cases when swarms of locusts completely darkened the sky for 250 km 2. Rough calculations show that approximately 35 billion insects that make up this swarm weigh 50 thousand tons. It is assumed that all the insects in such monstrous swarms weigh, apparently, only a quarter less than all the people on the planet! It's hard to believe...
The influence of locusts on the nature of Asia Minor and the Mediterranean can be assessed based on a quote from V.I. Vernadsky, in which he writes: “Several years ago I tried to more clearly express the weight of one cloud of locusts observed by Dr. Crowther over the Red Sea in 1889. before the organization of the international fight against locusts, the weight of this cloud was 4.4 * 10 7 tons. It was almost equal to the weight of copper, zinc and lead combined, produced by humanity during the (19th century) century. It’s like a rock in motion.” Let's add to this a mass with enormous potential for biological exchange!
An ecologist would most likely consider such a swarm of locusts, flying downwind thousands of kilometers from their permanent habitat, to be a population, but geneticists and evolutionists are careful not to apply this term to such groups.
Thus, to summarize, we can say that a population is a part of a species (consists of individuals of the same species), occupying a relatively homogeneous space and capable of self-regulation and maintaining a certain number. Each species within the occupied territory is thus divided into populations, i.e. consists of one or more populations, and a population is thus the form of existence of a species, its smallest evolving unit.
Any population is characterized by indicators unique to them and has a certain organization and structure. Such characteristics can be expressed by statistical functions, i.e. the population and its properties can be described using mathematics. These are, for example, structure, density, numbers, birth rates, and deaths. Some characteristics of populations are interrelated: mortality determines the structure, birth rate determines density, etc.
It should be emphasized that there is a fundamental difference between an individual organism and a population of organisms. Just as a drop of water does not reflect the properties of a river, lake, or ocean, an organism taken individually cannot characterize the entire population as a whole.
The only carrier of the characteristics of a population is a group of individuals, but not individual individuals in this group. An individual organism in a population is born, lives, dies, but ecologists are interested in this only as an opportunity, through the study of the behavior of an individual, to understand the properties of the group as a whole. The special properties inherent in a population reflect its state as a group of organisms as a whole, and not as individuals, i.e. the property of a population as a group of organisms is not a mechanical sum of the properties of each individual that composes it.
Populations are inherent as spatial (static) , so temporary (dynamic) characteristics. Spatial characteristics include total number, density, spatial distribution (dispersion), as well as various characteristics population structure- age (ratio of the number of individuals of different ages), sex (ratio of sexes). They characterize the state of the population at some point certain moment time t. Among the time (dynamic) characteristics, we note birth rate, death rate, growth rate, and growth curve. These indicators characterize the processes occurring in the population over a certain period of time D t. In addition, the population is characterized by complex relationships with its environment.
4.2. Spatial structure of populations.
Types spatial distribution
Under spatial structure population, the characteristics and nature of the distribution of population individuals in space are understood.
Spatial structure is important ecological significance. First of all, certain type use of the territory allows the population to effectively use environmental resources and reduce intraspecific competition. Efficient use of the environment and reduced competition between members of a population allow it to strengthen its position in relation to other species inhabiting a given ecosystem.
Another important significance of the spatial structure of a population is that it facilitates 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, settlement) and functions associated with participation in the ecosystem (participation in substance cycles, creation of biological products, and so on).
One of the important parameters that determine the spatial structure is the number of individuals in the population. Observing the properties of various populations, be they populations of animals or plants, one can see that their numbers vary greatly. It could be a hundred trees found on a hectare of pine forest, or millions unicellular algae in the ecosystem of a pond or lake, and several vultures living on inaccessible rocks, and clouds of starlings over a newly sown rye field.
Number of individuals in the population- one of the important characteristics when environmental research, especially when we're talking about about endangered species of plants and animals. Here we have to decide the question of acceptable minimum sizes populations in which it is capable of self-reproduction. Population size refers to the total number of individuals in a population.
When caring about preserving a species, a person must first of all think about preserving the population. For populations of various species, there are acceptable limits for the reduction in the number of individuals, beyond which the existence of the population becomes impossible. There are no exact data on critical values of population numbers in the literature. The given values are contradictory. However, the fact remains undoubted that the smaller the individuals, the higher the critical values of their numbers. For microorganisms this is millions of individuals, for insects – tens and hundreds of thousands, and for large mammals- A few dozens. The number should not decrease below the limits beyond which the probability of meeting sexual partners sharply decreases. The critical number also depends on other factors. For example, for some organisms a group lifestyle (colonies, flocks, herds) is specific. Groups within a population are relatively isolated. There may be cases when the population size as a whole is still quite large, and the number separate groups reduced below critical limits. For example, a colony (group) of a Peruvian cormorant should have a population of at least 10 thousand individuals, and a herd of reindeer - 300 - 400 heads.
Determining population size seems simple only at first glance. It’s good if we are dealing with individuals that permanently reside in a given territory: plants, sedentary, sedentary or large animals. In this case, the simplest way to determine the number is used - a simple count of all individuals.
In this case, all individuals can be counted visually without much error. Thus, wild reindeer of the Kola Peninsula in late winter - early spring accumulate on small mountain heights, where, thanks to thinner snow cover, they can get to the lichens that serve them as their main food at this time. Zoologists can fly by plane to places where animals gather and count the number of deer in the herd. In this case, it is possible to make a fairly accurate count of the individuals that make up the population.
It is even easier to count all the trees in a given forest area or herbaceous plants on a meadow plot. But what about, for example, migrating or nomadic animals, fish populations in water bodies, planktonic organisms, etc.?
Other estimates of population size are used here. For this purpose they are used various ways. One of them is tagging or banding. When animals are captured, some are tagged (random sampling) and then released back to mix with the rest of the population. After some time, a re-capture is carried out, another random sample is obtained and the proportion that is made up of marked individuals from total number caught. Then, based on the size of this proportion, the population size is determined.
Hydrobiologists studying small and minute benthic animals use a bottom grab tool, which allows them to estimate the number of individuals on a certain surface of the soil layer. Those studying plankton use a special device - a bathometer, which captures a certain volume of water with small organisms located there.
In the same cases when assess directly total number populations, plants or microorganisms is impossible, they resort to laying so-called trial census plots (round or square) or to taking separate samples and further counting the number of individuals in the resulting samples. The data obtained in this way allows one to estimate population density.
Population density is defined as the number of individuals of a species per unit area (mainly the earth's surface) or per unit volume ( water environment, experimental culture), for example, 200 trees per 1 hectare, 50 people per 1 km 2, 20 tadpoles per 1 m 3 of water. In some cases, this indicator is estimated through the number of encounters along the animal’s route (spring surveys based on the singing of male birds, assessment of migratory bird populations, winter counts of mammals based on tracks in the snow, etc.). The maximum density for different species of organisms and living conditions varies greatly. One hectare of land can contain significantly more plantains than, say, deer or wild boar. Some species of birds (penguins, seagulls) form so-called “bird colonies”. Not uncommon huge clusters pink flamingos on some lakes equatorial Africa. At the same time, many species of Central European forest songbirds never reach 1/10 of this density.
Distinguish average density, those. the number of individuals per unit of total space, and ecological density, i.e. number of individuals per unit of inhabited space.
The difference between these indicators can be understood from the example given by Yu. Odum for the wood stork living in a nature reserve in Florida. "In this area, the density of small fish with a drop in water level during the dry season winter season generally decreases, but ecological density increases, since as the water surface decreases, the number of fish per unit of water surface increases. Storks lay eggs at such a time that the hatching of the chicks occurs during the period of peak ecological density of fish. This makes it easier for parents to catch fish, which is the chicks' main food."
Individuals of living organisms (plants, animals, microorganisms) are usually distributed unevenly in space. The reasons for this can be very different: the influence of changing environmental factors, intra- and interspecific relationships of organisms, human influence, etc. That is why, when studying individual populations, an ecologist must always keep in mind that the representativeness of the sample (the correspondence of the observation indicators to the actual characteristics of the object as a whole) depends not only on the size and method of sampling, but also on how these samples are located in space. To do this, it is necessary to know the patterns of spatial distribution of individuals that make up the population.
In general, three types of distribution of individuals can be distinguished: random, regular (uniform) and group (spotted, crowded, aggregated).
Random distribution occurs when organisms are distributed in a homogeneous environment. In this case, the strength and direction of the influence of abiotic and biotic factors randomly change in time and space. Random distribution does not occur very often in nature, although the very action of random natural factors is not uncommon in itself. This random distribution characteristic, for example, of spiders living on the forest floor.
Associated with this type of placement of individuals in a population is the concept of “risk distribution” ( spreading of risk), proposed by Dutch researchers P. Boer and J. Redingius. It states that the number of any species in nature is maintained at a certain level (more precisely, within certain boundaries) insofar as the risk of death of individuals from any unfavorable factors is randomly distributed in time and space. Thus, the mechanism of influence of unfavorable environmental factors on a population is determined by random processes. Therefore, the population, even if any part of it dies as a result of a catastrophic impact, will not be destroyed, because such disasters do not occur in all or many places at once.
Group (spotted) distribution is characteristic of many organisms that live not only in terrestrial but also in aquatic ecosystems. This is the most common type of distribution of individuals in natural populations. The placement of individuals in groups is primarily due to the micro-complexity of the environment and the mosaic nature of ecological conditions (“patterned environment”).
As a result of the accumulation of individuals, groups are formed different sizes. The formation of these groups occurs for various reasons: due to local differences in habitats, under the influence of daily and seasonal changes weather conditions; in connection with reproduction processes, etc.
There are many examples of such group distribution. Many fish move from place to place in huge schools. Waterfowl gather in large flocks, preparing for long flights. Colonies of cormorants nesting on islands off the coast of Peru reach a population of 10,000 individuals with an average density of three nests per 1 m2. North American caribou reindeer form huge herds in the tundra. In the South American tropics, groups of ants, armed with powerful jaws and stings, line up in a 20-meter wide front and go on the attack, destroying along the way everyone who hesitates and is unable to escape.
The same examples can be given for plants: a spotty arrangement of clover plants in a meadow, spots of mosses and lichens in the tundra, a cluster of lingonberry shrubs in a pine forest, extensive spots of wood sorrel in spruce forest, strawberry meadows on light forest edges and so on.
Group placement of organisms is a unique adaptive factor in the life and functioning of populations of individual species. For example, in insects that form large groups, activity increases, individuals experience hormonal changes that accelerate their puberty and increasing fertility. Individuals forming groups are characterized by high survival rates. This optimization of physiological processes, leading to an increase in the viability of organisms, leading to an increase in their viability, is called the “group effect”.
The group effect is expressed in the optimization of physiological processes, leading to an increase in vitality when living together. It is most characteristic of animals and manifests itself in accelerated growth rates, increased fertility, faster formation of conditioned reflexes, increased average duration life etc. For example, in sheep outside the herd, the pulse and breathing quicken, and when they see an approaching herd, these processes normalize. In wintering fish, frogs, mollusks, and insects, there is a saving in energy costs during aggregations, which allows them to move more comfortably unfavourable conditions. Thus, even taking into account individual unfavorable deviations, the group effect contributes to the prosperity, survival and sustainability of the group of organisms as a whole.
Regular (even) distribution can be observed when there is strong antagonism of individuals (competition), when the probability of finding one individual next to another is extremely low. In nature, this type of distribution is difficult to encounter, although it is often possible to observe the distribution of organisms deviating from random towards greater regularity. Most often, when illustrating this type of distribution, reference is made to the placement of trees in a forest, where competition for light is so high that they are spaced at a more or less uniform distance from each other. As a textbook example of uniform distribution, the distribution of the Tribolium beetle in flour is usually cited. However, such examples of “uniform” distribution are quite conditional.
Regular distribution can most often be observed in artificially created agricultural systems - gardens, orchards. So, when planting, you can evenly distribute apple trees in the garden using a measuring tape. You can plant bushes in your garden this way. berry crops, some vegetable plants.
4.3. Sexual structure of populations
The sexual structure of a population determines the ratio of individuals of different sexes in it. The genetic mechanism of sex determination ensures the segregation of offspring by sex in a ratio close to 1: 1. This is the so-called primary sex ratio. It is determined by genetic mechanisms - the uniformity of divergence of sex chromosomes. For example, in humans, XY chromosomes determine the development of the male sex, and XX chromosomes determine the development of the female sex. In this case, the primary sex ratio is 1:1, that is, equally probable.
However, in a population the sex ratio is usually not 1:1. The number of males and females is different. This is because sex-linked traits often determine significant differences in the physiology, ecology and behavior of males and females. In this regard, populations often exhibit more high probability death of representatives of either sex, which means the sex ratio in the population changes.
This sex ratio at birth and in the early stages of development of organisms, when various environmental factors are superimposed on genetic determination, is called secondary ratio. It can differ significantly from the primary one for a number of reasons: the selectivity of eggs to sperm carrying the X- or Y-chromosome, the unequal ability of such sperm 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. Thus, in ants, fertilization is ensured at temperatures above 20 o C, and at more low temperatures unfertilized eggs are laid. The latter hatch into males, and from the fertilized ones, predominantly females.
In some species, sex is initially determined not by genetics, but by environmental factors. For example, a root vegetable from the araceae family, Arizema japonica, produces plants with female flowers only from the largest and most well-developed tubers. Small and weak tubers produce plants with male flowers.
In some animals (for example, amphibians), environmental factors such as temperature, hormone levels and concentrations can influence development in such a way that sex differences differ from the primary chromosome set. Thus, in Central European populations grass frog the appearance of young animals reflects the appearance of females. Only by the end of the second year of life, half of them turn into males.
In ants, bees and other social insects, the number of queens (females capable of sexual reproduction) in the population is regulated by workers through specific nutrition.
The sex ratio among sexually mature, reproducing individuals is called tertiary ratio . The sexual composition at this stage of development of organisms is very dynamic and changeable. Marked for humans and other mammals general pattern, which consists in reducing the proportion of males in older age groups Oh.
For example, in humans the secondary sex ratio is 100 girls to 106 boys. Upon reaching the age of 18, this ratio evens out due to increased male mortality. By age 50, the tertiary ratio is already 85 men per 100 women, and by age 80, 50 men per 100 women.
It should be noted that sexual structure, that is, sex ratio, is directly related to population reproduction and its sustainability.
4.4. Age structure of populations
An important characteristic when studying a population is its age structure, affecting both fertility and mortality. The ratio of different age groups in a population determines its ability to reproduce and shows the prospects of the population. In rapidly growing populations, young individuals make up a large proportion. Therefore, the state of the population after a certain period of time will depend on its current sex and age composition.
Interaction of populations of different species - section Ecology. Individual elements of the habitat of organisms are called environmental factors. They are divided into three large groups, inhabiting the same territory, the populations necessarily interact with each other...
Competition occurs when different species have similar needs for living conditions, food, and space. Competition is one of the manifestations of the struggle for existence.
Predation - relationships in which individuals of one species eat individuals of another species.
Symbiosis (mutualism) - relationships in which each species benefits from its association with another species. IN Lately Symbiosis refers to several forms of relationships between organisms (mutualism - mutually beneficial cohabitation, commensalism - freeloading, synoikia - tenantry), and not just mutualism.
ECOLOGICAL SYSTEMS
Historically established communities of populations of various species inhabiting a certain territory or water area, interconnected, mutually influencing each other, are called biocenoses.
The environment and biocenosis are connected by flows of matter and energy. Organisms absorb substances and energy from the environment, and return metabolic products and energy to it in the form of heat. Thus, the biocenosis and the environment constitute an inextricable unity, one complex system, which is called an ecosystem or biogeocenosis.
Biogeocenosis is a complex of interconnected populations of different species living in an area with more or less homogeneous living conditions. The dimensions of the biogenocenosis range from several hundred m2 to several km2, and vertically from several cm (on rocks) to several hundred meters (in the forest).
The connection between the components of biogeocenosis arises on the basis of food relationships. There are three types of food chains:
Chain eating: plants - herbivores - predators (grass → grasshoppers → oriole → snake → kite).
Chain decompositions: plant and animal remains - small carnivores, fungi, bacteria.
Food chains cannot be long, because each subsequent consumer, eating the previous one, spends a significant part of the energy on its vital activity. Only 5-20% of the energy passes into the newly built substance of the consumer's body. Therefore usually food chain has 3-5 links. When moving from one level to another, the number of individuals decreases and their size increases. Thus, approximately 9 million plants grow on 1 hectare of meadow (I nutritional level); 700,000 herbivorous insects feed on them (level II); they are eaten by 350,000 predatory insects and spiders (level III); which are food for three birds (level IV). As we can see, an ecological pyramid has formed, the base of which is 3 million times wider than the top. There are three types ecological pyramids:
- pyramid of numbers (at each level the number of individual organisms is plotted);
- biomass pyramid (characterizes the total mass of organisms at each level);
- energy pyramid (shows the amount of energy flow or productivity at successive levels).
In general, terrestrial biogeocenoses, where producers are large and live relatively long, are characterized by relatively stable pyramids of biomass with a wide base. In aquatic ecosystems, where producers are small in size and have short life cycles, the pyramid of biomass can be inverted or inverted (with the tip pointing down). Similar pyramids of biomass are observed in the ocean. Ocean phytoplankton are small in size and mass, but reproduce very intensively. The annual production of phytoplankton is hundreds of times higher than the harvest, i.e. phytomass attributed to a given point in time. However, all primary production is quickly eaten by consumers (zooplankton, lower crustaceans), and biomass accumulation practically does not occur. At the same time, zoomass accumulates in the ocean, because these organisms are larger and reproduce slowly. Thus, at the moment it turns out that there are more consumers than producers, and the pyramid of biomass has an inverted appearance compared to the pyramid of terrestrial biomass.
The population pyramid can also have an inverted appearance, for example, it can live and feed on one tree big number insects
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Individual elements of the habitat of organisms are called environmental factors. They are divided into three large groups
Fundamentals of ecology.. ecology is the science of the relationships between individual organisms or their communities and their habitat; ecology studies three..
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This term has other meanings, see Competition. Competition in biology, any antagonistic relationship associated with the struggle for existence, for dominance, for food, space and other resources between organisms or species ... Wikipedia
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- (from Lat. com “with”, “together” and mensa “table”, “meal”; literally “at the table”, “at the same table”; formerly communion) a way of coexistence (symbiosis) of two different types of living organisms, in which one population benefits... Wikipedia
- (from other Greek ἀντι against, βίος life) antagonistic relationships between species, when one organism limits the capabilities of another, the impossibility of coexistence of organisms, for example due to intoxication by some organisms (antibiotics, ... ... Wikipedia
This term has other meanings, see Symbiosis (meanings). Clown fish and sea anemone organisms coexisting in mutualistic symbiosis ... Wikipedia
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The request "Predator" is redirected here; see also other meanings. The request "Predators" redirects here; see also other meanings... Wikipedia
Between two ants of the species Oecophylla longinoda. Thailand. Trophallaxis ... Wikipedia
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Books
- Semiotic theory of biological life, N. A. Zarenkov. Is it possible to understand what life is by limiting ourselves to the study of the flesh of organisms - signs of life: molecules, chromosomes, cells, tissues and organs? IN this book a negative answer is justified...