Characteristics of populations in ecology. The main characteristics of the population. Environmental Population Strategies
Populations: structure and dynamics Lecture 7.
Moskalyuk T.A.
List of references
Stepanovskikh A.S. General ecology: Textbook for universities. M .: UNITY, 2001.510 p.
Radkevich V.A. Ecology. Minsk: Higher School, 1998.159 s.
Bigon M., Harper J., Townsend K. Ecology. Individuals, Populations, and Communities / Transl. from English M .: Mir, 1989. Vol. 2 ..
Shilov I.A. Ecology. M.: Higher School, 2003.512 p. (LIGHT, loops)
1. The concept of a population. Types of populations
2. The main characteristics of populations
3. The structure and dynamics of populations
4. The dual nature of population systems
a) the evolutionary and functional nature of the population
b) biological inconsistency of population functions (Lotka – Volterra model; law of emergence)
5. Fluctuations in numbers
6. Ecological population strategies
1. 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 (Micr otis gregalis). The common squirrel species has about 20 geographical populations, or subspecies.
2. The main 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.
Stable, growing and shrinking populations.The population adapts to changing environmental conditions by updating and replacing individuals, i.e. processes of birth (renewal) and decrease (death), complemented by migration processes. In a stable population, the birth and death rates are close and balanced. They may be unstable, but the population density is slightly different from some average value. The range of the species is neither increasing nor decreasing.
In a growing population, fertility exceeds mortality. Growing populations are characterized by outbreaks of mass reproduction, especially in small animals (locusts, 28-point potato bugs, Colorado potato beetles, rodents, crows, sparrows; from plants - ragweed, Sosnowski hogweed in the northern Komi Republic, dandelion, Himalayan, partly oak) Mongolian). Populations of large animals often grow under the conditions of the conservation regime (elk in the Magadan reserve, Alaska, sika deer in the Ussuri reserve, elephants in the Kenya national park) or introductions (elk in the Leningrad region, muskrat in Eastern Europe, domestic cats in separate families) . When re-compaction in plants (usually coincides with the onset of closure of the cover, crown canopy), differentiation of individuals in size and state of life begins, self-thinning of populations, and in animals (usually coincides with the achievement of puberty of young animals), migration to adjacent free areas begins.
If mortality exceeds fertility, then such a population is considered declining. In the natural environment, it is reduced to a certain limit, and then the birth rate (fertility) again increases and the population from the declining becomes growing. Most often, populations of undesirable species are excessively growing, declining - rare, relic, valuable, both economically and aesthetically.
3. The structure and dynamics of populations
The dynamics, condition, and reproduction of populations are consistent with their age and gender structure. The age structure reflects the rate of population renewal and the interaction of age groups with the environment. It depends on the features of the life cycle, which varies significantly between different species (for example, birds and mammals of predators), and external conditions.
In the life cycle of individuals, three age periods are usually distinguished: pre-reproductive, reproductive and post-reproductive. The plants are also characterized by a period of primary dormancy, which they pass in the stage of singing seeds. Each of the periods can be represented by one (simple structure) or several (complex structure) age stages. Annual structures, many insects, have a simple age structure. The complex structure is characteristic of trees of different ages, for highly organized animals. The more complex the structure, the higher the adaptive capacity of the population.
One of the most famous classifications of animals by age G.A. Novikov:
Newborns - until the moment of sight;
Young - growing individuals, "adolescents";
Semi-adult - close to sexually mature individuals;
Adults are sexually mature animals;
Old - individuals that have ceased to breed.
In geobotany, the classification of plants by age N.M. Chernova, A.M. Old:
Resting seeds;
Sprouts (seedlings) - plants of the first year of life, many of them live at the expense of nutrients in the cotyledons;
Juvenile - go on to self-nutrition, but in size and morphologically still different from adult plants;
Immature - possess transitional characteristics from juvenile to adult plants, are still very small, they have a change in the type of growth, the branching of shoots begins;
Virginia - "adult teens", can reach the size of adults, but there are no regenerative organs;
Young generative - the presence of generative organs is characteristic, the formation of the appearance typical of an adult plant is being completed;
Middle-aged generative - differ in maximum annual growth and maximum reproduction;
Old generative - plants continue to bear fruit, but they completely stop the growth of shoots and root formation;
Sub-senile - bear fruit very weakly, vegetative organs die off, shoots are neoplasm due to sleeping buds;
Senile - very old, decrepit individuals, features of juvenile plants appear: large single leaves, shoots overgrown.
Coenopopulation, in which all of these stages are presented, is called normal full member.
In forestry and taxation, classification of stands and stands by age classes is accepted. For conifers:
Sprouts and self-sowing - 1-10 years, height up to 25 cm;
Stage of young growth - 10-40 years, height from 25 to 5 m; under the forest canopy corresponds to small (up to 0.7 m), medium (0.7-1.5 m) and large-sized (\u003e 1.5 m) undergrowth;
Stage of the pole - middle-aged stands 50-60 years old; trunk diameters from 5 to 10 cm, height - up to 6-8 m; under the forest canopy, the young generation of the stand, or tonkomer with similar dimensions;
Ripening stands - 80-100 years; in size they can slightly inferior to the mother trees, in the open and in open woods they abundantly bear fruit; in the forest can still be in the second tier, do not bear fruit; in no case shall be assigned to the cabin;
Ripe forest stands - 120 years and older, trees of the first tier and trees of the second tier lagging in growth; bear fruit abundantly, at the beginning of this stage they reach technical ripeness, at the end - biological;
Perestoyny - over 180 years old, continue to bear fruit abundantly, but gradually become decrepit and dry out or fall out while they are still alive.
For hardwoods, gradations and grades are similar in size, but due to their faster growth and aging, their age class is not 20, but 10 years.
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The ratio of age groups in the population structure characterize its ability to reproduce and survive, and is consistent with fertility and mortality rates. Young (non-reproductive) individuals predominate in growing populations with high fertility (Fig. 2), while in stable populations they are usually of different ages, full-bodied populations, in which a regularly determined number of individuals pass from younger age groups to older ones, the birth rate is equal to the decrease in population. In declining populations, the basis is made up of old individuals; regeneration is absent in them or only slightly. |
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Sexual structure according to genetic laws, it should be represented by an equal ratio of males and females, i.e. 1: 1. But due to the specifics of physiology and ecology inherent to different sexes, due to their different viability, the influence of environmental factors, social, anthropogenic, there may be significant differences in this ratio. And these differences are not the same in different populations, as well as in different age groups of the same population. This is clearly shown in fig. 3, representing sections of the age and gender structure for the population of the former USSR and the African Republic of Kenya. In the context of the USSR, against the background of the natural distribution of age groups in the life cycle, a decrease in the birth rate during the war years and its increase in the postwar years is evident. The imbalance between the female and male gender is also undoubtedly associated with the war. In Kenya, there is a logical relationship between the distribution of sexes and the apparent population decline in pre-reproductive age with a low standard of living, depending on natural conditions. |
The study of the sexual structure of populations is very important, because both environmental and behavioral differences are strongly expressed between individuals of different sexes.
EXAMPLE.Males and females of mosquitoes (family Culicidae) differ greatly among themselves: in terms of growth rates, puberty, and resistance to temperature changes. Males in the adult stage do not eat at all or eat nectar, and females need to drink blood to fully fertilize the eggs. In some species of flies, populations consist of only females.
There are species in which sex was initially determined not by genetic, but by environmental factors, as, for example, in Japanese Arisema, when tuber mass is formed, female inflorescences are formed on plants with large fleshy tubers, and male ones on plants with small flesh. The role of environmental factors in the formation of the sexual structure in species with alternating sexual and parthenogenetic generations is well traced. At the optimum temperature in daphnia (Daphnia magna), the parthenogenetic females form the population, and when deviating from it, males also appear.
The spatial distribution of individuals in populations is random, group and uniform.
Random (diffuse) distribution - uneven, observed in a homogeneous environment; relationships between individuals are poorly expressed. Random distribution is characteristic of populations in the initial period of settlement; plant populations experiencing severe oppression by community edificators; animal populations whose social connection is poorly expressed.
EXAMPLESAt the initial stages of settlement and survival - insects pests on the field; sprouting of explant (pioneer) species: willow, chosenia, larch, woodpecker, etc., in disturbed areas (mountain ranges, quarries);
Group distribution is most common; reflects heterogeneity of living conditions or different ontogenetic (age) patterns of the population. It provides the greatest sustainability of the population.
EXAMPLES No matter how homogeneous the structure of the forest may seem, there is no such uniformity in the distribution of vegetation as in a field or on a lawn. The more pronounced the microrelief, which determines the microclimate in the forest community, the more pronounced the different ages of the stand, the more clearly expressed the parcellular structure of the plantation. Herbivorous animals unite in herds to successfully resist predator enemies. Group character is characteristic for sedentary and small animals.
Uniform placement in nature is rare. They are characterized by secondary forest stands of equal age after closure of crowns and intensive self-thinning, rare-growing stands growing in a homogeneous environment, unpretentious plants of lower tiers. Most predator animals leading an active lifestyle are also characterized by even distribution after they have settled and occupied the entire habitable territory.
How to determine the nature of plant placement?
This can be done using the simplest mathematical processing of accounting data. The plot or trial area is divided into registration sites of the same size - at least 25, or plants are counted at located at approximately the same distance accounting areas of the same size. The set of sites is a sample. Denoting the average number of individuals of the species at sites in the sample by the letter m, the number of sites (counts) in the sample is n, the actual number of individuals of the species at each site is x, one can determine the variance, or the scattering measure s2 (deviation of the value of x from m):
s2 \u003d S (m-x) 2 / (n-1)
With a random distribution s2 \u003d m (assuming a sufficient sample size). With a uniform distribution, s2 \u003d 0, and the number of individuals on each site should be equal to the average. With a group distribution, always s2\u003e m, and the greater the difference between the deviation and the average, the more pronounced is the group distribution of individuals.
4. The dual nature of population systems
a) the evolutionary and functional nature of the population
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Attention should be paid to the dual position of the population in the ranks of biological systems belonging to different levels of organization of living matter (Fig. 4). On the one hand, the population is one of the links in the genetic evolutionary series, which reflects the phylogenetic relationships of taxa of different levels, as a result of the evolution of life forms: organism - population - species - genus - ... - kingdom In this series, the population acts as a form of existence of a species whose main function is survival and reproduction. Playing an important role in the microevolutionary process, a population is an elementary genetic unit of a species. Individuals in a population possess characteristic features of structure, physiology, and behavior, i.e. heterogeneity. These features are developed under the influence of living conditions and are the result of microevolution taking place in a particular population. Changing populations in the process of adaptation to changing environmental factors and fixing these changes in the gene pool determines the evolution of the species. |
On the other hand, under the same specific environmental conditions, the population enters into trophic and other relationships with populations of other species, forming simple and complex biogeocenoses with them. In this case, it is a functional subsystem of biogeocenosis and represents one of the links of the functional-energy series:
organism - population - biogeocenosis - biosphere
b) biological inconsistency of population functions
The "duality" of populations is also manifested in the biological inconsistency of their functions. They are composed of individuals of the same species, and, therefore, are identical in environmental requirements to environmental conditions, and have the same adaptation mechanisms. But the populations themselves contain:
1) a high probability of acute intraspecific competition
2) the possibility of the absence of stable contacts and interconnections between individuals.
Intense competition takes place during overpopulation, leading to the depletion of life-supporting resources: in animals, food, plants moisture, fertility and (or) light. If the number of individuals is too small, the population loses the properties of the system, its stability decreases. The resolution of this contradiction is the main condition for maintaining the integrity of the system. It consists in the need to maintain an optimal number and an optimal ratio between the intra-population processes of differentiation and integration.
Trays – Volterra model. As an example of the natural regulation of the process of intraspecific competition, the Lotka – Volterra rule can be cited, which reflects the relationship in the food chain of consumers and producers, or a predator and prey. It is represented by two equations. The first expresses the success of the victim’s meetings with the predator:
Fertility naturally depends on the efficiency (f) with which food passes into offspring, and on the rate of food intake (a × C "× N).
The growth in the number and density of populations is not endless. Sooner or later, there is a threat of a lack of environmental resources (feed, shelters, breeding places, soil depletion, excessive shading). Each population has its own resource limits, called environmental capacity. As it decreases, intraspecific competition intensifies. Different mechanisms of regulation of numbers are included. In plants, self-thinning and differentiation of plants by size and physiological state begins, in animals fertility decreases, aggression intensifies, they begin to settle in free territories, epidemics begin within populations. The reaction of each species to its own overpopulation is different, but the result is the same for all - inhibition of development and reproduction.
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In fig. 5 depicts the Lotka – Volterra graphical model. It allows us to show the main trend in the predator-prey relationship, which consists in the fact that fluctuations in the number of predator populations are consistent with fluctuations in the prey population. Moreover, the cycles of increase and decrease in the number of predators and prey are shifted in relation to each other. When the number of preys is high (food resource), the number of predators increases, but not infinitely, but until there is tension with food. A decrease in food supplies leads to increased intraspecific competition and a decrease in the number of predators, and this, in turn, again leads to an increase in the number of prey. |
The law of emergence. As an integrated system, a population can be stable only with close contacts and interaction of individuals with each other. Only a herd can resist artiodactyl predators. Only in a pack do wolves hunt successfully. In forest communities, as a rule, undergrowth of trees grows better in biogroups (group effect), forest restoration in disturbed areas is better with plentiful seeding and friendly emergence of tree shoots. Animals live in herds, birds and fish in packs.
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Moreover, the population, as a system, acquires new properties that are not equivalent to a simple sum of similar properties of individuals in the population. For example, when daphnia, the food of perch, is knocked together in a group, a protective biofield is formed in the group (Fig. 5), due to which fish do not “notice” the food. One daphnia does not have such a biofield, and it quickly becomes prey for fish. The same pattern also manifests itself in the unification of populations into a system of biocenosis — in this case, the biocenosis obtains such properties that none of its blocks individually possess. This law - the law of emergence, was formulated by N.F. By reimers. |
5. Fluctuations in numbers
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Under favorable conditions, an increase in population is observed in populations and can be so rapid that it leads to a population explosion. The totality of all factors contributing to population growth is called biotic potential. It is high enough for different species, but the probability of the population reaching the population limit in vivo is low, because this is opposed by limiting (limiting) factors. The set of factors limiting the growth of the population is called environmental resistance. The equilibrium state between the biotic potential of the species and the resistance of the medium (Fig. 6), which maintains a constant population size, is called homeostasis or dynamic equilibrium. If it is violated, fluctuations in the population number occur, i.e., changes in it. |
Distinguish periodic and non-periodic fluctuations in the number of populations. The former occur within a season or several years (4 years — a periodic cycle of fruiting of cedar, increase in the number of lemmings, arctic fox, polar owl; apple trees in orchard plots bear fruit in a year), the latter are outbreaks of mass reproduction of some pests of useful plants, if environmental conditions are disturbed habitats (droughts, unusually cold or warm winters, too rainy vegetation seasons), unforeseen migrations to new habitats. Periodic and non-periodic fluctuations in the number of populations under the influence of biotic and abiotic environmental factors, characteristic of all populations, are called population waves.
Any population has a strictly defined structure: genetic, gender and age, spatial, etc., but it cannot consist of fewer individuals than is necessary for the stable development and resistance of the population to environmental factors. This is the principle of minimum population size. Any deviation of the population parameters from the optimal ones is undesirable, but if their excessively high values \u200b\u200bdo not pose a direct danger to the existence of the species, then a decrease to the minimum level, especially the population size, poses a threat to the species.
EXAMPLESThe minimum size of the populations is characterized by very many species in the Far East: the Amur tiger, the Far Eastern leopard, the polar bear, the mandarin duck, many butterflies: the Maca tail and the Xusa tail, the admiral, marshmallows, the beautiful Artemis, Apollon, the relic barbel, and the stag beetle; from plants: all araliaceae, orchids, whole-leaved fir, densely flowered pine, Manchurian apricot, solid juniper, yew spiky, two-row lily, calloused, Daurian lily, etc., Ussuri grouse, Kamchatka trillium and many other species.
However, along with the principle of minimum population size, there is also the principle, or rule, of a population maximum. It lies in the fact that the population cannot increase indefinitely. Only theoretically is it capable of unlimited growth in numbers.
According to the theory of H.G. Andrevarty - L.K. Bircha (1954) - the theory of population limits, the number of natural populations is limited by the depletion of food resources and breeding conditions, the inaccessibility of these resources, too short a period of accelerated population growth. The theory of "limits" is supplemented by the theory of biocenotic regulation of the population size of K. Fredericks (1927): the growth of the population size is limited by the influence of a complex of abiotic and biotic environmental factors.
What are these factors or causes of fluctuations?
Sufficient stocks of food and its lack;
Competition of several populations due to one ecological niche;
External (abiotic) environmental conditions: hydrothermal regime, illumination, acidity, aeration, etc.
6. Ecological population strategies
No matter what the individuals adapt to living together in the population, whatever the adaptation of the population to one or another factor, all of them are ultimately aimed at long-term survival and continuation of themselves in any living conditions. Among all the devices and features, one can distinguish a complex of basic features, which are called environmental strategy. This is a general characteristic of the growth and reproduction of this species, including the growth rate of individuals, the period they reach puberty, the frequency of reproduction, age limit, etc.
Environmental strategies are very diverse and although there are many transitions between them, two extreme types can be distinguished from them: r-strategy and K-strategy.
r-strategy- fast breeding species (r-species) possess it; it is characterized by selection for increasing the population growth rate in periods of low density. It is characteristic of populations in an environment with abrupt and unpredictable changes in conditions or in ephemeral, i.e. existing for a short time (drying puddles, water meadows, temporary streams)
The main features of the r-species are: high fertility, short regeneration time, high abundance, usually small individuals (small seeds in plants), short lifespan, high energy consumption for reproduction, short habitats, low competitiveness. R-species quickly and in large numbers populate unoccupied territories, but, as a rule, soon - during the life of one or two generations are replaced by K-species.
The r-species includes bacteria, all annual plants (weeds) and pests (aphids, leaf beetles, stem pests, herd locust phase). From perennials - pioneer species: Ivan tea, many cereals, wormwood, ephemeral plants, from woody species - willow, white and stone birch, aspen, chosenia, from coniferous - larch; they appear first on disturbed lands: burnt areas, mountain ranges, construction pits, along roadsides.
K-strategy - species with a low breeding rate and high survival rate (K-species) have this strategy; it determines the selection for increased survival with a high population density approaching the limit.
The main features of K-species: low fecundity, significant life expectancy, large sizes of individuals and seeds, powerful root systems, high competitiveness, stability on the occupied territory, high specialization of lifestyle. The breeding rate of K-species with approaching the limiting population density decreases and rapidly increases at low density; parents care about their descendants. K-species often become dominant biogeocenoses.
K-species include all predators, humans, relic insects (large tropical butterflies, including Far Eastern, relic barbel, stag beetle, ground beetles, etc.), a single locust phase, almost all trees and shrubs. The most striking representatives of plants are all conifers, Mongolian oak, Manchurian walnut, hazel, maple, forbs, sedge.
Different populations use the same habitat in different ways, therefore, both types of strategies can exist in it at the same time.
EXAMPLES In the forests, on the ecological profile of “Gornotaiga” in the spring, before the leaves bloom on the trees, ephemeroids rush to bloom, bear fruit and finish the vegetation: Corydalis, Amur adonis, anemones, oriental violet (yellow). Under the forest canopy, flowering of peonies, lilies, and Vorontsa spiky begins. In open areas in dry oak forests of the southern slope, sheep fescue and pink mariannik grow. Oak, fescue, and other species are K-strategists, Mariannik is an r-strategist. Forty years ago, after a fire, aspen (r-species) parcels formed in the fir-broad-leaved type of forest. Currently, aspen leaves the stand, giving way to K-species: linden, oak, hornbeam, walnut, etc.
Any population of plants, animals and microorganisms is a perfect living system, capable of self-regulation, restoration of its dynamic equilibrium. But it does not exist in isolation, but in conjunction with populations of other species, forming biocenoses. Therefore, interpopulation mechanisms regulating the relationships between populations of different species are widespread in nature. A biogeocenosis, consisting of many populations of different species, acts as a regulator of these relationships. In each of these populations, interactions between individuals occur, and each population has an effect on other populations and on the biogeocenosis as a whole, just like a biogeocenosis with the populations included in it has a direct effect on each specific population.
As I.I. writes Schmalhausen: "... In all biological systems, there is always the interaction of different cycles of regulation, leading to self-development of the system according to the given conditions of existence ..."
When optimal ratios are reached, a more or less prolonged stationary state (dynamic equilibrium) of a given system occurs under given conditions of existence. "... For a population, this means the establishment of a certain genetic structure, including various forms of balanced polymorphism. For a species, this means the establishment and maintenance of a more or less complex structure. ... For biogeocenosis, this means the establishment and maintenance of its heterogeneous composition and the existing relationships between components When the conditions of existence change, the stationary state, of course, is violated. There is a reassessment of the norm and options, and, therefore, a new transformation, that is neck ... the self-development of these systems. " Moreover, in the biogeocenosis, the relationships between the links change, and in the populations, the genetic structure is being restructured.
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Abundance and density are the main parameters of the population.
Number - the total number of individuals in a given territory or in a given volume.
Density - the number of individuals or their biomass per unit area or volume. In nature, there are constant fluctuations in numbers and density.
Population dynamics and density is determined mainly by fertility, mortality and migration processes. These are indicators characterizing the change in the population over a certain period: month, season, year, etc. The study of these processes and their underlying causes is very important for predicting the state of populations.
Fertility is distinguished between absolute and specific. Absolute birth rate Is the number of new individuals that appeared per unit of time, and specific- the same number, but assigned to a certain number of individuals. For example, a person’s birth rate is the number of children born per 1,000 people during the year. Fertility is determined by many factors: environmental conditions, food availability, species biology (puberty rate, number of generations during the season, ratio of males and females in the population).
According to the rule of maximum fertility (reproduction) under ideal conditions, the maximum possible number of new individuals appears in populations; fertility is limited by the physiological characteristics of the species.
Example: Dandelion in 10 years is able to fill the entire globe, provided that all its seeds sprout. Extremely abundant seeds of willow, poplar, birch, aspen, most weeds. Bacteria divide every 20 minutes and for 36 hours can cover the entire planet with a continuous layer. Fertility is very high in most species of insects and low in predators, large mammals.
Mortality, like fertility, it is absolute (the number of individuals that died in a certain time), and specific. It characterizes the rate of population decline from death due to diseases, old age, predators, lack of food, and plays a major role in the dynamics of the population.
There are three types of mortality:
The same at all stages of development; It is rare in optimal conditions;
Increased mortality at an early age; characteristic for most species of plants and animals (less than 1% of seedlings survive by age of maturity in trees, 1-2% of fry in fish, less than 0.5% of larvae in insects);
High death in old age; usually observed in animals whose larval stages pass under favorable slightly changing conditions: soil, wood, living organisms.
Stable, growing and shrinking populations
The population adapts to changing environmental conditions by updating and replacing individuals, i.e. processes of birth (renewal) and decrease (death), complemented by migration processes. In a stable population, the birth and death rates are close and balanced. They may be unstable, but the population density is slightly different from some average value. The range of the species is neither increasing nor decreasing.
In a growing population, fertility exceeds mortality. Growing populations are characterized by outbreaks of mass reproduction, especially in small animals (locusts, 28-point potato bugs, Colorado potato beetles, rodents, crows, sparrows; from plants - ragweed, Sosnowski hogweed in the northern Komi Republic, dandelion, Himalayan, partly oak) stuck Mongolian). Populations of large animals often grow under the conditions of the conservation regime (moose in the Magadan reserve, Alaska, sika deer in the Ussuri reserve, elephants in the Kenya national park) or introductions (elk in the Leningrad region, muskrat in Eastern Europe, domestic cats in separate families) . When re-compaction in plants (usually coincides with the onset of closure of the cover, crown canopy), differentiation of individuals in size and state of life begins, self-thinning of populations, and in animals (usually coincides with the achievement of puberty of young animals), migration to adjacent free areas begins.
If mortality exceeds fertility, then such a population is considered declining. In the natural environment, it is reduced to a certain limit, and then the birth rate (fertility) again increases and the population from the declining becomes growing. Most often, populations of undesirable species are excessively growing, declining - rare, relic, valuable, both economically and aesthetically.
Population structure
Under demographic structure populations, first of all, understand its gender and age composition. In addition, it is customary to talk about spatial structure population - that is, about the features of the distribution of individuals in space.
Knowledge of the structure of the population allows the researcher to draw conclusions about its well-being or disadvantage. For example, if in a population there are no generative (that is, able to give offspring) individuals and there are many old-aged (senile) individuals, then an unfavorable prognosis can be made. Such a population may not have a future. It is desirable to study the structure of the population in dynamics: knowing its change over several years, one can speak much more confidently about certain trends.
Age structure of the population
This type of structure is associated with the ratio of individuals of different ages in the population. Individuals of the same age are usually combined in cohorts, that is, age groups.
The age structure of plant populations is described in great detail. The following ages (age groups of organisms) are distinguished in it (according to T.A. Robotnov):
- latent period - the state of the seed;
- pregenerative period (includes the conditions of a seedling, juvenile plant, immature plant and virgin plant);
- generative period (usually divided into three subperiods - young, mature and old generative individuals);
- postgenerative period (includes the state of the sub-senile plant, senile plant and the dying phase).
In animal populations, various age stages can also be distinguished. For example, insects that develop with complete metamorphosis go through the stages of an egg, larva, pupa, and adult (adult insect). In other animals (developing without metamorphosis), various age-related states can also be distinguished, although the boundaries between them may not be so clear.
Sexual structure of the population
The sexual structure, that is, the sex ratio, is directly related to the reproduction of the population and its stability.
It is customary to distinguish the primary, secondary and tertiary sex ratios in the population. Primary sex ratio determined by genetic mechanisms - the uniformity of the divergence of sex chromosomes. For example, in humans, the XY chromosomes determine the development of the male, and XX - the female. In this case, the primary sex ratio is 1: 1, that is, it is equally probable.
Secondary sex ratio - This is the sex ratio at the time of birth (among newborns). It can differ significantly from the primary one for a number of reasons: the selectivity of the ovum to spermatozoa bearing the X- or Y-chromosome, the unequal ability of such sperm to fertilize, and various external factors. For example, zoologists describe the effect of temperature on the secondary sex ratio of reptiles. A similar pattern is typical for some insects. So, in ants, fertilization is provided at temperatures above 20 ° C, and at lower temperatures unfertilized eggs are laid. Males hatch from the latter, and females from the fertilized ones — predominantly.
Tertiary sex ratio is the sex ratio among adult animals.
Spatial structure of the population
The spatial structure of the population reflects the nature of the distribution of individuals in space.
There are three main types of distribution of individuals in space:
- uniform (individuals are distributed uniformly in space, at equal distances from each other), the type is also called uniform distribution;
- congregational, or mosaic (that is, "spotted", individuals are located in isolated clusters);
- random, or diffuse (individuals are randomly distributed in space).
Uniform distribution is rare in nature and is most often caused by intense intraspecific competition (as, for example, in predatory fish).
Random distribution can be observed only in a homogeneous environment and only in species that do not show any desire for grouping. As a textbook example of uniform distribution, the distribution of the Tribolium beetle in flour is usually given.
Group distribution is much more common. It is associated with the characteristics of the microenvironment or with the features of the behavior of animals.
The spatial structure is of great environmental importance. First of all, a certain type of use of the territory allows the population to efficiently use environmental resources and reduce intraspecific competition. Efficiency of using the environment and reducing competition between representatives of the population allow it to strengthen its position in relation to other species inhabiting this ecosystem.
Another important value of the spatial structure of the population is that it provides for the interaction of individuals within the population. Without a certain level of intrapopulation contacts, the population will not be able to perform both its species functions (reproduction, resettlement) and the functions associated with participation in the ecosystem (participation in the circulation of substances, creation of biological products, and so on).
Population Properties: self-reproduction, variability, interaction with other populations, sustainability.
Ecologically, the population is characterized by a value estimated by the occupied territory (area), the number of individuals, age and gender composition. Range Sizes depend on the radii of the individual activity of organisms of a given species and the characteristics of natural conditions in the corresponding territory. Number of individuals in populations of organisms of different species varies. So, the number of dragonflies Leucorrhinia albifrons in the population on one of the lakes near Moscow reached 30,000, while the number of earthen snails Cepaea nemoralis estimated at 1000 copies. There are minimal abundance values \u200b\u200bat which a population is able to maintain itself over time. A reduction in numbers below this minimum leads to the extinction of the population.
The size of the population is constantly fluctuating, which depends on changes in the environmental situation. So, in the fall of a year favorable in terms of feed conditions, the population of wild rabbits on one of the islands off the southwestern coast of England consisted of 10,000 individuals. After a cold low-feed winter, the number of individuals decreased to 100.
Age structure populations of organisms of different species varies depending on life expectancy, reproduction intensity, age of puberty. Depending on the type of organisms, it can be more or less complex. So, in herd mammals, such as beluga dolphins Delphinapterus leucas, in the population at the same time there are calves of the current year of birth, young growth of the last year of birth, matured, but usually not breeding animals at the age of 2-3 years, adult breeding individuals at the age of 4-20 years. On the other hand, in shrews Sorex In the spring, 1-2 offspring are born, after which adult individuals die out, so in autumn the entire population consists of young immature animals.
Sexual composition populations is determined by evolutionarily fixed mechanisms of formation of the primary (at the time of conception), secondary (at the time of birth) and tertiary (in the adult state) sex ratios. As an example, consider the change in the sexual composition of a population of people. At the time of birth, it is 106 boys per 100 girls, equalized at the age of 16-18, at the age of 50 it is 85 men per 100 women, and at the age of 80 it is 50 men per 100 women.
Genetic characteristics of the population
Genetically, a population is characterized by its gene pool (allele pool). It is represented by a set of alleles that form the genotypes of the organisms of a given population. The gene pools of natural populations are distinguished by hereditary diversity (genetic heterogeneity, or polymorphism), genetic unity, dynamic equilibrium of the proportion of individuals with different genotypes.
Hereditary diversity consists in the presence in the gene pool of simultaneously different alleles of individual genes. Initially, it is created by a mutational process. Mutations, being usually recessive and not affecting the phenotypes of heterozygous organisms, are preserved in the gene pools of populations in a state hidden from natural selection. Accumulating, they form reserve of hereditary variation. Due to combinational variability, this reserve is used to create new combinations of alleles in each generation. The volume of such a reserve is huge. So, when crossing organisms differing in 1000 loci, each of which is represented by ten alleles, the number of genotype variants reaches 10 1000, which exceeds the number of electrons in the Universe.
Genetic unity the population is determined by a sufficient level of panmixia. Under conditions of random selection of mating individuals, the entire gene pool of the population is the source of alleles for the genotypes of organisms of successive generations. Genetic unity is also manifested in the general genotypic variability of the population with changing living conditions, which determines both the survival of the species and the formation of new species.
The main environmental characteristics of the population
1. What is a population?
2. Can a species consist of one population?
3. What is the role populations in evolution?
Environmentalists studying functioning ecological systems, consisting of objects of animate and inanimate nature, consider populations as the main elements of each ecosystem. It is thanks to the functioning of populations that conditions are created that support life. In biotic communities, each population plays a role assigned to it, together with the populations of other species, constituting a certain natural unity, developing and acting according to its own laws.
To understand the functioning of this complex system, it is very important to know not only the biology features of certain types of organisms, but the main thing is their population characteristics, in particular the density of settlement, the total strength individuals, growth rate, life expectancy, the number of offspring produced. These characteristics, called population demographics, are critical to anticipating possible changes that occur in individual populations as well as in the entire community or ecosystem.
Demographic characteristics, such as fertility, mortality, age composition (structure) and number of individuals (abundance), characterize the population as a whole, reflecting the speed of the processes occurring in it. Separate organism born, aging and dying. In relation to an individual, one cannot talk about fertility, mortality, age structure, abundance - characteristics that make sense only at the group level.
In the best way, the population as a group of organisms is characterized by abundance. A measure of abundance may be the total population size or its total biomass. However, the measurement of these indicators in relation to many animals is associated with great difficulties.
Therefore, density is often used as an indicator of abundance.
Population density is the number of individuals, or their biomass, per unit area or volume of living space. Examples of population density are: 500 trees per 1 ha of forest, 5 million individuals of chlorella per 1 m 3 of water, or 200 kg of fish per 1 ha of the surface of a reservoir. Density measurement is used in cases where it is more important to know not a specific size of a population at a given point in time, but its dynamics, that is, the course of changes in numbers over time;
Fertility is the number of new individuals (also eggs, seeds) born (hatched, laid) in a population over a certain period of time. Fertility characterizes the ability of a population to increase in number due to the reproduction of individuals.
Distinguish between maximum fertility (sometimes called physiological or absolute) and environmental, or simply fertility. Maximum fertility is the theoretical maximum speed education new individuals in ideal conditions, when there are no external factors restraining the processes of reproduction. Obviously, the maximum birth rate is largely determined by the ability of females to simultaneously produce any amount of offspring, i.e., physiological fecundity.
Ecological fertility gives an idea of \u200b\u200bthe rate of increase in population under actually existing living conditions of the considered group of individuals.
Ecological fertility is unstable and varies depending on the physical conditions of the environment and the composition of the population.
In general, species that do not care about offspring are characterized by high potential and low ecological fertility. So, for example, an adult female cod swallows millions of eggs, of which only 2 individuals survive to adulthood.
If you trace the fate of a certain group of individuals born at the same time, it is easy to find that their number continuously decreases over time as a result of the death of some individuals. The death rate of organisms is called mortality and can characterize individual population subgroups or the population as a whole.
Mortality is determined not only by the size of the population, but also by the average life expectancy of the organisms included in it. The higher the mortality rate, the lower the average life expectancy, and vice versa.
The age structure of the population is characterized by the ratio of the number or biomass of individuals of different ages. This ratio is called the age distribution of the population, i.e., the distribution of numbers by age groups. The age composition of the population depends on the intensity of mortality of organisms and on the birth rate.
Even within the same population, significant changes in the age structure can occur over time. Such changes, however, would automatically include mechanisms that again return the population to a certain normal age distribution characteristic of a given population.
An analysis of the age structure allows predicting the number of populations for a number of the next generations and years, which is used, for example, to assess the possibilities of fishing, in hunting, in some zoological studies.
The characteristics of the age structure determine many properties of the population as a system. A population that includes many age groups is less affected by factors that determine the success of breeding in a particular year. Indeed, even extremely unfavorable breeding conditions that can lead to the complete death of an offspring of a given year are not catastrophic for a population of a complex structure, because the same parental pairs participate in reproduction many times.
Demographic characteristics: abundance, density, birth rate, mortality. Age structure.
1. In one lake live perches, ruffs, crucian carp, pike, roach. Perch, pike, pike perch, bream, roach live in the neighboring reservoir isolated from the first one. How many species and how many populations inhabit both reservoirs?
2. What are population demographics? How to use them in economic activity?
3. 3. What is the practical significance of studying populations? Give examples.?
4. What properties of a population are determined by the characteristics of its age composition?
5. 5. Why do populations of different ages turn out to be less sensitive to sudden short-term changes in reproduction conditions.?
At the beginning of the season, 1000 fish were tagged. During the subsequent fishing, 350 tagged were found in the total catch of 5000 fish. What was the population before fishing?
Kamensky A.A., Kriksunov E.V., Pasechnik V.V. Biology Grade 10
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DEMECOLOGY - studies the relationship of populations with the environment, demography and a number of other characteristics of populations in the light of their relationship with the environment
By definition of Nikolai Fedorovich Reimers:
POPULATION - an elementary grouping of individuals of one species, occupying a certain territory and having all the necessary conditions to maintain its stability for a long time in changing environmental conditions.
S.S. Schwartz gives a definition of a population from an evolutionary-ecological perspective. A POPULATION is a collection of individuals of the same species that have a common gene pool and inhabit a certain space, with relatively uniform living conditions.
Features of the population:
The probability of frequent crosses
Habitat specificity
the ability to transmit hereditary information
Populations is an open system, of great importance, since at the level of populations occur
adaptations
natural selection
evolutionary change
Any population is characterized by a number of characteristics, has a certain structure and organization. It should be noted that the special properties inherent in a population reflect its state as a group of organisms as a whole, rather than individual individuals, i.e. the property of a population as a group of organisms is not the mechanical sum of the properties of each individual composing it
Populations have spatial (static) and temporal (dynamic) characteristics.
Spatial
total strength
density
spatial distribution (variance)
structure (age and gender composition)
They characterize the state of the population at some particular point in time t
Temporary characteristics include
birth rate
mortality
growth curve.
They characterize the processes occurring in the population over a certain period of time Δt
SPATIAL or static characteristics.
NUMBER OF SPECIES IN A POPULATION - the total number of individuals in a given territory or in a given volume.
Especially important when it comes to rare and endangered species
Methods for determining abundance:
simple calculation (not suitable for everyone, only for inactive, settled animals or plants);
tagging and ringing (random sampling is marked and released, after some time re-capture and setting the proportion of tagged individuals from the total number of caught)
sampling (counting microorganisms) EXAMPLE on fluctuations in the number of red locusts in Africa in 1962 in the south of Morocco destroyed 7 thousand tons of oranges annual consumption of France
DENSITY OF POPULATION - the number of individuals of a species per unit area or unit volume. For example, 200 kg of fish per 1 ha of a reservoir, or 5 million diatoms per 1 m3 of water, 500 trees per 1 ha, etc. Sometimes it is important to distinguish between average (abundance / biomass per unit of total space) and ecological density (abundance / biomass per unit of habitable space, that is, per unit area or volume that can actually be occupied by a given population).
SPATIAL DISTRIBUTION Three types of distribution of individuals of populations are distinguished: group, random and uniform.
Uniform distribution occurs where competition between individuals is very strong or antagonism (implacable hostility) exists. EXAMPLE: In trees in the forest, competition for light is very high, so there is a tendency to stand at approximately equal distances from each other. In the chaos of bird colonies, nests are located at such distances from each other so that individuals sitting on the nest could not peck each other. This type of distribution is found among predators with a clear territoriality - predators "mark" the territory for protection from competitors. Rarely in nature, but can be artificially created by humans (orchards, sowing crops).
Group distribution is the most common type in natural ecosystems and is a kind of adaptive factor in the functioning of populations. There are a lot of EXAMPLES. Huge schools of fish, flocks of birds during flights, colonies of nesting birds move from place to place. Due to the fact that the environmental conditions are different in different places, individuals usually accumulate where the environment is most favorable for them. For example, salamanders are distributed in the forest crowded under fallen trees, where the humidity is high.
TEMPORARY OR DYNAMIC CHARACTERISTICS
Fertility is the ability of a population to increase in numbers (reproduction). Usually, fertility is expressed as the rate determined by dividing the total number of individuals that appear by a certain period of time - an hour, a day, or a year (total fertility). Distinguish between the maximum (absolute) birth rate - the theoretical maximum rate of formation of new individuals under ideal conditions, and ecological (realized) birth rate - an increase in population under actual environmental conditions.
MORTALITY reflects the death of individuals in a population. It can be expressed by the number of individuals that died during this period. Environmental mortality - the death of individuals in these environmental conditions. The value is not constant; it varies depending on environmental conditions and the state of the population. Theoretical minimum mortality - a constant value for a given population. Even in the most ideal conditions, individuals will die of old age. This age is determined by the physiological life expectancy, which, of course, often exceeds the ecological life expectancy.
POPULATION GROWTH is the difference between fertility and mortality.
Populations regulate their numbers by updating or replacing individuals. Individuals appear in the population due to birth and immigration, and disappear as a result of mortality and emigration.
With a balanced intensity of fertility and mortality, a stable population is formed.
Often there is an excess of fertility over mortality, the population increases to such an extent that there may be an outbreak of mass reproduction. Such populations are called growing. (Colorado potato beetle, muskrat of 5 individuals in 1905 in the vicinity of Prague).
However, when the population is overdeveloped, the living conditions of the population worsen, which causes its overconsolidation, leads to a sharp increase in mortality, and the number begins to decline. If mortality exceeds fertility, the population becomes declining. (populations of sables, beavers, bison, sparrows in Prague).
The concept of a population in ecology
The degree of isolation of populations
If the members of a species constantly move and shuffle over vast spaces, such a species is characterized by a small number of large populations. Reindeer and arctic foxes, for example, are distinguished by great migration abilities. Labeling results show that Arctic foxes travel hundreds, and sometimes more than a thousand kilometers, from breeding sites over the season. Reindeers make regular seasonal migrations also on a scale of hundreds of kilometers. The boundaries between populations of such species usually pass through large geographical barriers: wide rivers, straits, mountain ranges, etc. In some cases, a moving species with a relatively small range can be represented by a single population, for example, a Caucasian tour, whose herds constantly roam two main ranges of this mountain range.
With poorly developed abilities to move, many small populations are formed in the composition of the species, reflecting the mosaic landscape. In plants and sedentary animals, the number of populations is directly dependent on the degree of heterogeneity of the environment. For example, in mountainous regions, the territorial differentiation of such species is always more complicated than in flat open spaces. An example of a species in which the multiplicity of populations is determined not so much by differentiation of the environment as by features of behavior is a brown bear. Bears are highly attached to their habitats, therefore, within the vast range are represented by many relatively small groups that differ from each other in a number of properties.
The degree of isolation of neighboring populations of the species is very different. In some cases, they are sharply divided by the territory unsuitable for habitation, and are clearly localized in space, for example, perch and tench populations in lakes isolated from each other or populations of plate-toothed rat, white-headed whale, Indian warbler and other species in oases and river valleys among deserts.
The opposite option is the continuous occupation of large areas with a view. This distribution pattern is characteristic, for example, of small gophers in dry steppes and semi-deserts. In these landscapes, their population density is universally high. Some unsuitable for living areas are easily overcome during the resettlement of young animals, and in favorable years, temporary settlements arise on them. Here, the boundaries between populations can only be distinguished conditionally, between regions with different population densities.
Another example of the continuous distribution of a species is a seven-point ladybug. These beetles are found in a wide variety of biotopes and different natural zones. The species is also characterized by pre-winter migrations. Borders between populations in such cases are almost not expressed. However, since cohabiting individuals contact with each other more often than with representatives of other parts of the range, the population of places remote from each other can be considered different populations.
Within the same species, there can be populations with both clearly distinguishable and smeared boundaries (Fig.
8.1. The concept of a population in ecology
A population in ecology is a group of individuals of the same species interacting with each other and co-inhabiting a common territory.
The word "population" comes from the Latin "populus" - people, population. Thus, an ecological population can be defined as a population of one species in a certain territory.
Members of the same population exert no less influence on each other than physical environmental factors or other types of organisms living together. In populations, all forms of relationships characteristic of interspecific relations are manifested to one degree or another, but the most pronounced are the mutualistic (mutually useful) and competitive ones. Specific intraspecific relationships are relations associated with reproduction: between individuals of different sexes and between parent and daughter generations.
During sexual reproduction, gene exchange turns a population into a relatively holistic genetic system. If cross-fertilization is absent and vegetative, parthenogenetic, or other methods of propagation predominate, the genetic connections are weaker and the population is a system of clones, or clean lines sharing the medium. Such populations are united mainly by ecological ties. In all cases, laws are in force in populations to allow the use of limited environmental resources in this way to ensure that offspring are left behind. This is achieved mainly through quantitative changes in the population. Populations of many species have properties that allow them to control their numbers.
Maintaining optimal abundance under the given conditions is called population homeostasis. The homeostatic capabilities of populations are expressed differently in different species. They are also carried out through the relationships of individuals.
Thus, populations, as group associations, have a number of specific properties that are not inherent in each individual.
The main characteristics of populations:
1) number - the total number of individuals in the allocated territory;
2) population density - the average number of individuals per unit area or volume of space occupied by the population; population density can also be expressed in terms of the mass of members of the population per unit space;
3) fertility - the number of new individuals that appeared per unit time as a result of reproduction;
4) mortality - an indicator that reflects the number of deaths in a population of individuals over a certain period of time;
5) population growth - the difference between fertility and mortality; growth can be both positive and negative;
6) growth rate - the average growth per unit of time.
A specific organization is characteristic of populations. The distribution of individuals by territory, the ratio of groups by gender, age, morphological, physiological, behavioral and genetic characteristics reflect the structure of the population. It is formed, on the one hand, on the basis of the general biological properties of the species, and on the other, under the influence of abiotic environmental factors and populations of other species. The population structure is therefore adaptive. Different populations of the same species have both similar structural features, and distinctive, characterizing the specifics of environmental conditions in their habitats.
Thus, in addition to the adaptive capabilities of individual individuals, the population of a species in a certain territory is also characterized by adaptive features of group organization, which are the properties of a population as a supra-individual system. The adaptive capabilities of the species as a whole as a system of populations are much wider than the adaptive characteristics of each particular individual.
8.2. The population structure of the species
Each species, occupying a certain territory (area), is represented on it by a system of populations. The more complex the territory occupied by the species is divided, the more opportunities there are for the isolation of individual populations. However, to a no lesser extent the population structure of a species is determined by its biological characteristics, such as the mobility of its constituent individuals, the degree of their attachment to the territory, and the ability to overcome natural barriers.
