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4.3. Age structure

Age structure is determined by the ratio of different age groups of individuals in the population. Age, or ontogenetic, state is defined as the physiological and biochemical state of an individual, reflecting a certain stage of ontogenesis. Individuals of the same age state are functionally similar, but may have different absolute or calendar ages. Absolute age is measured by the lifetime of an organism or a given cohort of individuals in a population from the moment an individual appears to the time of observation. In the population and in the cenosis, not the absolute age, but the age state reflects the biological role of individuals, and therefore a comparative assessment of the role of species in the community is carried out on them.

Age structure of populations in plants. A complex of qualitative traits is used as the basis for identifying the age states of plants. The expression of ontogenetic states are mainly morphological changes, which are most easily visually perceived and correlatively associated with other age-related changes in the body.

The idea of ​​age as a stage of individual development of an individual formed the basis of numerous periodizations of morphogenesis. The classification of the age conditions of plants by Rabotnov (1950) is generally accepted. According to his classification, 11 age states are distinguished in plants, corresponding to four periods of ontogeny (Table 3). The ratios of the duration of these periods are very different in different species (Fig. 44).

Rice. 44. The ratio of the duration of the pre-reproductive (7), reproductive (2) and post-reproductive (2) periods of ontogeny in some species (according to A.V. Yablokov, 1987)

dormant seeds- seeds (embryonic individuals) separated from the parent individual and after dissemination independently exist in the soil (on the soil).

sprouts- small non-branching plants with the presence of germinal structures (cotyledons, germinal root, shoots with small, simpler leaves than in an adult plant) and mixed nutrition (due to seed substances, assimilation of cotyledons and first leaves). With above-ground germination, the cotyledons are taken out above the level of the soil surface; when underground (near oak) - remain in the soil. The first leaves (in spruce) are thin, short (up to 1 cm long), rounded in cross section and often located.

Table 3

Classification of the age conditions of seed plants (according to Rabotnov, 1950)

*Indices of age conditions are taken according to A.A. Uranov (1973)

Juvenile plants - plants that have lost their connection with the seed, cotyledons, but have not yet acquired the features and characteristics of an adult plant. Differ in simplicity of the organization. They have childish (infantile) structures. Their leaves are small in size, not typical in shape (in spruce they are similar to the needles of seedlings), branching is absent. If branching is expressed, then it qualitatively differs from the branching of immature individuals. They are characterized by high shade tolerance, being part of the grass-shrub layer.

immature plants are characterized by transitional features and properties from juvenile to adult vegetative individuals. They are larger, with pronounced branching, develop leaves that are more similar in shape to the leaves of adult plants. Nutrition is autotrophic. At this stage, the main root dies off, adventitious roots and tillering shoots develop. Immature trees are part of the understory layer. In low light, individuals are delayed in development, and then die off. In juveniles, this stage, as a rule, is not recorded. In spruce, it is usually observed in the fourth year of life. Isolation of immature plants is most difficult, and some authors combine them into one group with virginal plants.

virginal plants have morphological features typical of the species, but do not yet develop generative organs. This is the phase of preparing the morphophysiological basis for achieving physiological maturity, which will come at the next stage. Virginal trees have nearly fully developed features of an adult tree. They have a well-developed trunk, crown, maximum growth in height. They are part of the tree canopy and experience the maximum need for light.

Generative young plants characterized by the appearance of the first generative organs. Flowering and fruiting is not plentiful, seed quality may still be low. In the body, complex rearrangements occur that ensure the generative process. The processes of neoplasms prevail over dying off. The growth of trees in height is intensive.

Generative mid-aged plants reach maximum sizes, are distinguished by large annual growth, abundant fruiting, high quality seeds. The processes of neoplasms and dying off are balanced. In trees, the apical growth of some large branches stops, dormant buds awaken on the trunks.

generative old plants- plants, the annual growth of which is weakened, the indicators of the generative sphere are sharply reduced, the processes of dying off prevail over the processes of neogenesis. Dormant buds are actively awakening in trees, the formation of a secondary crown is possible. Seeds are produced irregularly and in small quantities.

subsenile plants lose the ability to develop the generative sphere. The processes of dying off predominate, the secondary appearance of leaves of the transitional (immature) type is possible.

Senile plants characterized by features of general decrepitude, which is expressed in the death of parts of the crown, the absence of renewal buds and other neoplasms; a secondary appearance of some juvenile features is possible. Trees usually develop a secondary crown, the upper part of the crown and trunk dies off.

dying plants have single viable dormant buds, dead parts predominate.

The listed age conditions are typical for polycarpics. In monocarpics, the generative period is represented by only one age state, and the post-generative period is completely absent. Age conditions are determined by specially developed diagnoses and keys (Fig. 45, 46).

Age structure of animal populations. At animals are usually distinguished by young, underyearlings, yearlings, adults and old individuals. Some authors distinguish five age groups of animals: newborns (before the time of vision); young (growing individuals who have not yet reached puberty); semi-adult (close to puberty); adults (sexually mature individuals); old (individuals that have ceased to breed). V.E. Sidorovich distinguished three age groups in the Belarusian otter populations: young individuals (the first year of life), half-adults (the second year of life), and adults (the third year of life and older). In the Bialowieza bison population, adults account for 57.8%, young animals (from 1 to 3.5 years old) - 27.9, underyearlings - 14.3%.

The allocation of age groups in animals is difficult. Most often, attention is paid to the time of transition of an individual to a generative state. The age of puberty in different species occurs at different times. In addition, the timing of maturation of individuals of the same species in different populations is also different. In some populations of the ermine (Mustela erminea), the phenomenon of neoteny is manifested - mating of still blind 10-day-old females. Beluga females mature at 15–16 years old, males at 11 years old. Under favorable conditions, the beluga can enter rivers to spawn up to 9 times. During the river period of life, females do not feed. Re-maturation is observed after 4–8 years (females) and 4–7 years (males). The last spawning occurs at the age of about 50 years. The post-reproductive period lasts 6-8 years. Much earlier, at the age of 4 or 5, the sexual maturity of female polar bears begins. Reproduction proceeds until the age of 20, repeats on average after 2 years, the average litter size is 1.9 cubs. Age differences are most clearly manifested in species whose development proceeds with metamorphosis (egg, larva, pupa and adult).

Rice. 45. Age conditions of common spruce (according to Yu.E. Romanovsky, 2001):

j- juvenile; im- g- generative

Individuals of different age groups, both in plants and animals, inevitably developing under different conditions, noticeably differ not only in morphological, but also in quantitative indicators. They have biological and physiological differences, play different roles in the composition of communities, in biocenotic relations. In plant populations, seeds, for example, being at rest, express the potentialities of the population. Seedlings have mixed nutrition (endosperm nutrients and photosynthesis), juvenile individuals and individuals of subsequent groups are autotrophs. Generative plants perform the function of self-maintenance of the population. The role of individuals in the life of a population, starting from subsenile plants, is weakening. Dying plants leave the population. In the process of ontogenesis in many species, the life form changes, as well as the attitude, the degree of resistance to environmental factors.

Rice. 46. Age conditions of plantain medium (according to L.A. Zhukova, 1980):

j- juvenile; im- immature; v - virginal; g- generative young; g2– generative middle age; g 3 - generative old; ss- subsenile; s- senile

In animals, differences between age groups are also very significant and species-specific. In populations of bank voles (Clethrionomys glareolus), according to Shilov (1997), specimens of spring and summer cohorts mature quickly, marry early, and are distinguished by fecundity, contributing to an increase in the population size and an increase in its range. However, their teeth are quickly erased, they age early and live mostly 2-3 months. A small number of individuals survive until the spring of next year. As a rule, animals of the latest generations winter. They have a small body size, a significantly lower relative mass of most internal organs (liver, kidneys), a reduced rate of tooth wear, i.e., a sharp inhibition of growth is expressed. In addition, they have very low mortality in winter. According to the physiological state, wintering voles correspond to approximately one-month-old specimens of spring-summer generations. They give birth and soon die off. Their descendants are individuals of early spring cohorts, distinguished by early maturation and fecundity, quickly replenish the population thinned during the non-reproductive period, closing the annual cycle.

Due to the biological characteristics of hibernating individuals, energy costs are reduced to a minimum in the most difficult time for the population. They successfully "drag" the population through the winter. A similar pattern was noted in other rodent species. In steppe lemmings (Lagurus lagurus), born in May, the average age of reaching sexual maturity was 21.6 days, and those born in October, 140.9 days. According to Schwartz, the experience of adverse conditions occurs in a state of "conserved youth". The increase in the lifespan of rodents of late cohorts is not due to survival in old age, but through the prolongation of the physiologically youthful period.

The process of transition of a plant or animal from a virginal state to a generative state is determined by a specific genetic program and is regulated by many factors. For plants, this is primarily temperature, daylight hours, and position in the phytocenosis. The onset of adulthood of individuals in coeval cenoses of Siberian fir (Abies sibirica) ranges from 22 to 105 years. It has been noted that the initiation of the first generative organs in coniferous species occurs during the maximum growth of the tree in height, as well as during intensive radial growth of the trunk. The faster the growth curve goes up, the earlier the woody plant enters the reproductive phase. Physiological and structural changes in plants are associated with the maximum linear increase in height. Rapid growth allows plants to achieve a certain morphological structure and linear dimensions in a short time. With the attenuation of the climax of growth in height due to the redistribution of plastic substances, stable flowering and fruiting occurs. Herbaceous plants begin fruiting also at a certain threshold value of the vegetative mass and the development of storage organs.

According to M.G. Popov, as the amount of the meristem begins to decrease and “the body acquires a shell, an armor of permanent tissues”, its ability to grow decreases, the process of generative development begins, and with further depletion of the meristem, aging occurs. The mechanism of this phenomenon is very complex and not fully understood. It is assumed that quantitative changes in metabolism lead to the activation of inert genes, the synthesis of specific RNA and qualitatively new reproductive proteins. Yu.P. Altukhov showed that the greater the proportion of "heterotic" genes involved in the processes of growth and puberty, the greater the energy expenditure of the organism in the pregenerative period of ontogenesis and the earlier sexual maturity occurs.

Age spectra. Age structures of populations are expressed in the form of age spectra reflecting the distribution of individuals in a population by age states. The study of the age structure begins with the establishment of a basic age spectrum. Base age spectrum acts as a reference (typical), with which the age conditions of the studied populations of a given species are compared. It is considered as one of the biological indicators of the species, and deviations reflect the state of a particular cenopopulation.

There are four types of basic spectra (Fig. 47). Within each type, several options are distinguished depending on the methods of self-maintenance, the course of ontogenesis of individuals and the features of its implementation in the phytocenosis.

Left spectrum reflects the predominance in the population of individuals of the pregenerative period or one of its age groups. Typical for trees and some herbs.

Unimodal symmetric spectrum reflects the presence in the population of individuals of all age states with a predominance of mature generative individuals, which is usually expressed in species with weak aging.

Right hand spectrum characterized by a maximum of old generative or senile individuals. The accumulation of old individuals is most often associated with the long duration of the corresponding age states.

Rice. 47. Types of base spectra of cenopopulations (average indicators) (from L.B. Zaugolnova, L.A. Zhukova, A.S. Komarova, O.V. Smirnova, 1988):

a-left-sided (meadowsweet elmous); b - unimodal symmetrical (Valisian fescue); in– right-sided (meadow fescue); g - two-peaked (pinnate feather grass)

Bimodal (two-peak) spectrum has two maxima: one - in the young part, the other - in the composition of mature or old generative plants (two modal groups). It is typical for species with a significant lifespan and a well-defined aging period.

The ratio of age groups. According to the ratio of age groups, invasive, normal and regressive populations are distinguished. The classification was proposed by Rabotnov in accordance with the three stages of development of the cenopopulation as a system: emergence, full development and extinction.

The population is invasive consists mainly of young (pregenerative) individuals. This is a young population, which is characterized by the process of development of the territory and the introduction of rudiments from outside. She is not yet capable of self-sustaining. Such populations are usually characteristic of clearings, burnt areas, and disturbed habitats. They develop especially successfully in the field after continuous plowing. In addition to local species, invasive cenopopulations form woody introduced species. Irga spiky, vesicle calinophylla, banks pine, ash-leaved maple and some other species are introduced into natural undisturbed or slightly disturbed cenoses, without significantly affecting their overall structure. The implementation process is very complicated, associated with a lot of waste. Self-sowing of balsam fir, including seedlings, juvenile, immature, and virginal plants, was up to 40000 ind./ha under oxic growing conditions (left-handed spectrum). Over 12 years, it decreased to 14 thousand, and over the next 9 years, its number decreased to 6 thousand ind./ha. Getting under the canopy of the tree layer, virginal plants are characterized by slow development, many enter into secondary dormancy.

The population is normal includes all (or almost all) age groups of organisms. Differs in resistance, the ability to self-maintenance by seed or vegetative means, full participation in the structure of the biocenosis, independence from the external supply of rudiments. These populations are normal full members or normal incomplete. Populations with a full age spectrum are a characteristic feature of established communities.

The population is regressive 2
It is more correct to call it a "regressing population".

It is characterized by the predominance of post-generative age groups of individuals. Juveniles are absent. In such a state, populations lose the possibility of self-maintenance, gradually degrade and die. The regressive populations of drooping birch in forests include many of the oldest birch forests, in which the species does not regenerate under the birch canopy, and spruce undergrowth, which constitutes its invasive population, develops abundantly. In a degrading state, mainly due to the reclamation of the swamp massif, there was the only cenopopulation of white fir in Belarus (Belovezhskaya Pushcha).

Age states reflect the dynamic state of the population. In its development, it usually goes through invasive, normal and regressive stages. In each case, the age structure of the population is determined by the biological characteristics of the species and depends on environmental conditions. It should be guided by the exploitation of natural populations of animals and plants.

The value of different quality of age conditions. Different nutritional spectra of individuals of age groups soften intraspecific competitive relationships, resources are used more fully, and the population's resistance to adverse environmental factors increases, since individuals of different age states have different adaptive potential. Tadpoles, for example, are aquatic phytophages, frogs are zoophages leading a terrestrial lifestyle. Adult individuals of the May beetle (Melolontha hippocastani) feed on the leaves of trees, the larvae feed on humus and plant roots. The cohorts are confined to different soil layers and, depending on its temperature and humidity, and the availability of food, beetles fly out at different times, which endows the population with numerous adaptive strategies. The food of the cabbage butterfly (Pieris brassicae), the largest among the local garden whites, is the nectar of cruciferous plants, the food of caterpillars is cabbage leaves. At the same time, young caterpillars, grayish-green, with black dots and a light yellow stripe on the dorsal side, scrape off the flesh of the leaf; grown individuals make holes in the leaves small holes; caterpillars of older ages, painted green, with bright black spots and three bright yellow stripes, eat the entire leaf, except for large veins. Younger larvae of the common mole cricket (Gryllotalpa gryllotalpa) feed on humus and plant roots growing into the nesting chamber. The main food of older larvae and adults are earthworms, insect larvae, underground parts of plants, which causes great damage to cultivated plants, especially in vegetable gardens and greenhouses.

Age heterogeneity is also important for the exchange of information between individuals and serves the purposes of continuity in the population.

Sex structure- the numerical ratio of males and females in different age groups of the population. It is typical for populations of dioecious individuals (it is most clearly expressed in arthropods and vertebrates) and dioecious plants, which make up about 4% in the temperate zone of the northern hemisphere. Traditionally, the sex structure of seed plant populations is determined by the ratio of individuals with pistillate, staminate, and bisexual flowers. The program for the development of pistillate and staminate flowers is quite complex. The sex of the flower is regulated by the concentration of auxins in the roots of plants, controlled by the level of ploidy of the genomes, as well as by the signal coming from the external environment. For example, in hemp (Cannabis sativa) under low light and lack of moisture, plants with bisexual flowers appear with a fairly high frequency.

The sexual structure is dynamic, closely related to the age structure of the population and the living conditions of individuals. Primary sex ratio is determined during the formation of zygotes by genetic mechanisms based on the heterogeneity of the sex chromosomes (X- and Y-chromosomes) (Fig. 48). In mammals and in many species of other animals, females are homogametic (the set of sex chromosomes XX), while males are heterogametic (XY).

Rice. 48. Scheme of the genetic mechanism of sex determination on the example of gamete fusion in mammals (from I.A. Shilov, 1997)

In birds and butterflies, on the contrary, the heterogametic sex is represented by females, while males are homogametic. In the process of meiosis, different combinations of sex chromosomes obtained from different parents are possible, which determines the sex of each individual in the offspring. In this case, there is usually an equal sex ratio (1:1). The only mammals with a genetically determined excess of females in their populations are the wood lemming (Myopus schisticolor) and the hoofed lemming (Dicrostonyx torquatus). In these species, in addition to the wild-type X chromosome (X 0), there is a mutant chromosome that induces the development of individuals with the XY karyotype along the female pathway. These females are widely distributed in populations and are distinguished by fertility.

However, in the process of development, the potential capabilities of the fetus are violated by the action of various reasons, and at birth the real ratio of male and female individuals turns out to be different. This ratio among newborns and juveniles is secondary sex ratio. The mechanism of sex redefinition under the influence of environmental factors, physiological causes, different mortality of fetuses of different sexes, which are superimposed on genetic conditioning, is especially pronounced at the embryonic and larval stages of ontogenesis. Thus, in many species of reptiles, the temperature of egg incubation is of primary importance for the formation of sex. In crocodiles, an equal number of males and females appear at a nest temperature of 32–33 °C. At lower temperatures (below 31 °C), only females develop, and at higher temperatures (above 33.5 °C), only males develop. In the marine worm (Bonellia viridis), free-floating larvae in the water become females. The larvae, which attach themselves to the proboscis of an adult female on the 4th-6th day of development and are influenced by the substances she secretes, develop into males.

A change in the number of male and female individuals also occurs in the process of ontogeny of individuals in a population. As a result, among adults in the population, a new tertiary sex ratio, which is determined by various reasons. It may be the result of differential mortality of males and females. In connection with the increased mortality of bison males in Belovezhskaya Pushcha, since 1983, there has been a tendency to reduce the number of mature males. The sex ratio is 1:1.6, and among adults - 1:2.3. There are more males in populations of rare (endangered) birds. Females often die in nests while incubating. Stress, heavy physical activity shorten their life expectancy.

The sex ratio also depends on the characteristics of the development of species. For example, polychaetes (Ophryotrocha puerilis) and gastropods (Crepidula plana) are males at the beginning of puberty with small body sizes, and with an increase in size they begin to produce eggs. In some species of fish, young individuals function as males, and old ones function as females. The ecologically complicated structure of populations in some species is achieved due to the presence of dwarf forms in the population along with individuals of normal size. In the tunja (Salvelinus leucomaenis), dwarf males do not make the usual migration to the sea for other individuals. Reproduction occurs at a young age. After reproduction, individuals do not die, but continue to develop like ordinary juveniles (Yablokov, 1987).

An important role in sex determination in dioecious plants is played by ecological and coenotic conditions, especially trophicity and soil moisture. Male individuals dominate more often in extreme conditions with a low level of vitality, which is noted in the cenopopulations of the sorrel (Rumex acetosella) and other herbaceous species. Females are more demanding on the richness of the soil. According to our data, they prevailed and were noticeably higher on rich fresh soils in cenopopulations of stinging nettle. In some cenopopulations, female and male individuals form two canopies. The ratio of male and female individuals of the common marchantia (Marchanthia polymorpha) depends on the degree of moisture. With an increase in moisture, the proportion of males increases markedly.

Sex ratios vary widely across species. In many mammals, fish, the tertiary ratio is 1:1, in humans the secondary ratio is 1:1, but with age it shifts towards women due to their longer life span. The secondary sex ratio in penguin populations is 1:1, the tertiary is 1:2. The gray monitor lizard has 22 females for 65 males. An excess of females has been observed in lemming populations. In bats, after wintering, the proportion of females sometimes decreases to 20%, and in some birds (pheasants, great tits), a higher mortality is characteristic of males. According to F.S. Kokhmanyuk, in 1976 females prevailed in the Minsk, Grodno and Armavir populations of the Colorado potato beetle (over 90%); in Gomel, Brest and Sochi - males (70–91%). The following year, in the Grodno population of the species, the sex ratio was 1:1.

In populations, an individual trend of changing the sex ratio is expressed. This phenomenon, which is very dynamic and multifactorial, leads to a complication of the structure of the population. Each population is characterized not only by a certain numerical ratio of males and females in different age structures, but also by the proportion of different types of males and females, the proportion of sterile individuals, as well as individuals with different sets of sex chromosomes (Yablokov, 1987). The sex ratio determines the intensity of reproduction and the general biological potential of the population (Shilov, 1997).

V.N. Bolypakov and B.S. Kubantsev, summarizing the material on the characteristics of the sexual structure of animals, distinguish four types of dynamics of the sexual structure of the population.

Unstable sex composition characteristic of animals with a short life cycle, high fertility and mortality (among mammals it is typical for insectivorous species). The sex ratio (secondary and tertiary) changes frequently in different habitats and in relatively short periods of time.

Male-dominated composition characteristic of predatory animals with a pronounced form of care for offspring, whose populations do not reach a high density.

Female-dominated composition It is noted in such animals, the males of which have a shorter life expectancy and partially die off under adverse conditions. The life of females is longer, fertility is low (ungulates, pinnipeds).

Composition with a relatively equal number of males and females characteristic of highly specialized animals, often with high fertility (desman, mole, beaver, etc.).

Biological heterogeneity of male and female individuals. Nature has taken the path of separating the sexes, allowing, as Schwartz (1980) puts it, surprising extravagance by dividing individuals of a species into two genetically distinct groups (males and females). Physiological differences lead to ecological diversity, which is a guarantee of maintaining the heterogeneity of the population, especially in extremely unfavorable environmental conditions.

The biological heterogeneity of male and female individuals is manifested in the degree of resistance to environmental factors, in growth characteristics, puberty, behavioral reactions, lifestyle. Female plants are distinguished by their large size, shoot length, leaf size and shape, crown structure, better development of root systems, higher regenerative capacity, as well as greater demands on the richness of the soil and its water regime. Due to the greater degree of tissue watering, they are more mesophilic organisms. Male individuals are characterized by greater drought resistance, sensitivity to the adverse effects of low temperature, infection, and toxic substances. Sex differences in animals have been identified even in relation to the accumulation of heavy metals, for example, in male swimming beetles (Dytiscus marginalis). Some species have differences in nutrition, which reduces intraspecific competition. Thus, female mosquitoes (family Culicidae) are blood-sucking, while males either do not feed at all, or feed only on dew or nectar. The unequal length of the beak in males and females of some birds makes it possible for individuals of the species to feed on different insects, and the different shape of the beaks simplifies, respectively, the joint extraction of insects from under the bark.

M.G. Popov (1983) believed that the sexual process does not have the primary purpose of reproduction, it is characteristic of highly organized creatures, but even they, such as insects, can develop without fertilization. Popov considered it to be a "permanent apparatus of variability" providing adaptation.

By age. This is the most important component of the population structure.

1. Age structure of plant populations

In populations of perennial plants, all individuals are characterized by a set of biomorphic features that determine their age differentiation. For population studies, the definition of age states (biological age) is much more important than absolute age (calendar age). Based on a complex of qualitative traits, 4 periods and a maximum of 11 age states are distinguished in plant ontogeny:

I) latent (seeds) - characterized by long-term storage, constitutes the very reserve of the population; II) pregenerative (seedlings, juveniles, immature, virginal) - the development of plants before the appearance of generative shoots; III) generative (young, medium, old) - the formation of generative shoots; IV) senile (subsenile, senile, dying) - simplification of life forms and death.

The processes of neogenesis and accumulation of energy predominate towards the average generative state, and after that, the processes of death and energy loss.

The age structure is one of the most important characteristics of a population. The age spectrum reflects the vital state of the species in the cenosis, as well as such important processes as reproduction intensity, mortality rate, and the rate of generation change. The ability of the population system to self-maintenance and the degree of its resistance to the influence of negative environmental factors, including anthropogenic pressure, depend on this side of the structural organization. It also characterizes the stage of development of the population (wykovist), and, consequently, the prospects for development in the future.

1.1. Population types

There are three main types of populations depending on the stage:

• invasive - the population is not yet capable of self-maintenance, depends on the introduction of seeds from outside, consists mainly of pregenerative individuals,
• normal - self-maintenance occurs, mainly generative plants predominate,
• regressive - loss of the ability to self-sustain, post-generative predominate.

Among normals, there are polynomials and non-polynomials if any age groups are missing, most often through a break in "insparmation", the extinction of certain age groups, or internal factors that control the development of the population itself. With the predominance of a normal population in the age spectrum of individuals of a certain age group, young, mature, aging and old are distinguished.

1.2. Basic age spectra

With a fairly complete imagination about biology and ecological and phytocenotic confinement of a species, basic age spectra are distinguished (modal characteristics of normal populations in an equilibrium state). There are four main types that are distinguished by the position of the absolute maximum in the spectra of age states:

Type I - complete predominance of young individuals; II - generative; III - old generative or senile; IV-determined by two peaks in the old and young parts of the population (bimodal).

Literature

• Krichfalushi VV, Mezev-Krichfalushi GM Population biology of plants. - Uzhgorod., 1994.
• Mezev-Krichfalushiy G.N. Population biology of the Umbelliferae and the prospects for its survival in Transcarpathia / / Ecology. - 1991. - No. 3.

counting units. Calculations of age (ontogenetic) spectra in plants are based on the isolation and use of counting units.

The issue of isolating a counting unit is rather complicated due to the ability of plants as modular organisms to form vegetative structures (partial bushes and shoots, tubers, bulbs, adventitious buds on roots, etc.) within a physically integral individual, capable of independent existence and development and protruding as a unit of environmental impact. In plant population studies, two counting units are used. The first unit is morphological; when such units are singled out, the main feature is the physical integrity of the analyzed structure, i.e. individuals. Such an approach is quite legitimate and expedient if the researcher is dealing with a single-stemmed tree, a compact bush, a bulbous plant, etc.

When the object of study is a physically integral system of root offspring, for example, aspen, consisting of mature, young trees, and shoots that have just begun to develop, it is physically impossible and inappropriate to single out morphological units from the point of view of analyzing the age and spatial structure of populations. In this regard, an idea was formed about the second - phytocenotic - counting unit.

Counting units differ significantly in plants of monocentric, explicitly polycentric, and implicitly polycentric biomorphs, identified on the basis of the characteristics of the spatial distribution of shoots, renewal buds, and roots (Smirnova, 1987).

Adult individuals of monocentric biomorphs are characterized by the fact that the roots, shoots (shoot) and renewal buds are concentrated in a single center, which is the center of growth of the individual and the center of influence on the environment. Adult specimens of clearly polycentric biomorphs have several clearly defined growth centers of the individual, which are a relatively autonomous part of the individual. Such centers can be partial bushes, and in the absence of branching (tillering) - partial shoots. Adult individuals of implicitly polycentric biomorphs, as in the previous type, have several growth centers (Smirnova, 1987), but in plant ontogeny these centers arise so close that it is practically difficult to distinguish between them. In this regard, an implicitly polycentric individual is conditionally considered as a single center of influence on the environment.

Types of ontogenetic (age) spectra of populations. The most easily defined sign of a stable state of a population is a full-fledged ontogenetic spectrum, in which the numerical ratio of individuals of different ontogenetic groups is determined by the biological properties of the species: 1) the total duration of ontogenesis and individual states; 2) the rate of development of individuals in different states; 3) the method of self-maintenance of populations: deeply rejuvenated diasporas (seeds and vegetative rudiments), shallowly rejuvenated vegetative individuals, or a different combination of the above methods; 4) the intensity and frequency of inspermation and elimination of individuals, 5) the ability to create a soil reserve of seeds, 6) the size of the area of ​​resource absorption by individuals of different ontogenetic states (synonymous - feeding area). Such spectra are called basic (characteristic); they characterize the definitive (dynamically stable) state of populations (Cenopopulations..., 1988).

The types of basic spectra are distinguished by the position of the absolute maximum in the spectrum of ontogenetic states. Within each type, depending on the method of self-maintenance of the population, variants are distinguished.

Specific spectra of populations can show both great similarity with the base spectra, and significantly differ from them. The variety of specific spectra can be combined into several types corresponding to a particular state (or life stage) of the population:

Invasive state - only pregenerative (sometimes young generative) plants are represented in the spectrum;

Normal condition:

A) a full-membered spectrum, in which all or almost all ontogenetic groups of plants (of seed and/or vegetative origin) are represented; it can be left-handed, unimodal (with a maximum on generative plants) and right-handed;

B) vegetative-full-member spectrum, where plants of only vegetative origin are represented;

C) a discontinuous spectrum, where most of the ontogenetic groups are represented;

Regressive state - the population consists only of post-generative plants;

A condition in which only some (often one) ontogenetic groups are represented - a fragmented spectrum.

Invasive populations are in their infancy and, depending on the ontogenetic composition and number of individuals, on the one hand, and ecological and cenotic conditions, on the other hand, have more or less probable prospects for development into normal populations. The latter are fully capable of spontaneous self-maintenance by seed and/or vegetative means. The absence of individual ontogenetic groups in the spectrum of normal populations may be associated with the periodicity of fruiting and, as a rule, is not evidence of an unstable state of the species in the community.

Populations become regressive when older plants stop producing or when conditions in the community prevent undergrowth from developing. In addition to the options listed above, in disturbed forest communities, populations can be represented by individual individuals of certain age conditions (population fragments). This usually indicates the episodic establishment of the species at an extremely low abundance level, and is characteristic of populations of assectator species. It is very difficult to assess the prospects for the development of such populations. Diagnostics of the state of populations, based on the above features, makes it possible to predict the further development of cenopopulations, and also allows us to approach the assessment of the successional state of the community. At the same time, for an adequate assessment of the prospects of the population, it is necessary to take into account the biological and ecological characteristics of the species.

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AGE SPECTRUM OF CENOPOPULATIONS

The distribution of individuals according to age states in a cenopopulation is called its age, or ontogenetic spectrum. It reflects the quantitative ratio of different age periods and stages. If all age groups are represented in the age spectrum, then the population is called full member.

If only young individuals that have not reached the reproductive phase of development are represented in the age spectrum, then the population is called invasive(introduced, expanded). An example of such a population is the pine (p. Pinus), developing at the site of a recent felling. If all or almost all age groups are represented in the age spectrum, then the population is complete and stable and is called normal. It is capable of self-maintenance in a generative or vegetative way. The normal type of populations is typical for the dominant species of the plant community, for example, the coenopopulation of the meadow foxtail ( Alopecurus pratensis) in a foxtail meadow or common blueberry ( Vaccinium myrtillus) in the blueberry-green-moss spruce forest. If the population contains mainly senile or subsenile individuals, and there is no renewal, then such a population is called regressive(fading). The number of individuals in it is steadily declining. Birch (b. Betula) in an overmature birch forest with dense spruce undergrowth (R. Rkea) may serve as an example of such a population. Shoots of birch do not develop due to shading by young spruces, therefore, its population is not capable of self-maintenance and is doomed to extinction. A similar situation occurs with English oak ( Quercus robur) in a 300-year-old oak forest.

The age composition of populations can be reflected in the form of a diagram, placing the quantitative ratio of age stages, starting from the virginal ones, one above the other. As a result, age pyramids are obtained, by the nature of which one can predict the future change in the population size. There are three main types of age pyramids corresponding to the three types of age composition of the population described above. A pyramid with a hypertrophied wide base reflects the invasive population. If the age pyramid is correct, then this is a normal population. An age pyramid with a narrow base is characteristic of a regressive population.

The analysis of the age composition of cenopopulations is of great importance for predicting changes in the plant community and is the biological basis for developing methods for the rational use of natural plant resources and their protection, identifying the possibilities of restoring vegetation on disturbed lands, and assessing the ecological valence of species.

ASSESSMENT OF THE STATE OF COENOPOPULATIONS OF WOODY PLANTS ACCORDING TO GEOBOTANICAL DESCRIPTIONS

In the case when it is not possible to carry out full-fledged studies of the coenopopulations of woody plants, it is possible to carry out an express assessment of their state in the phytocenosis according to typical geobotanical descriptions, which indicate the abundance of species in each tier of the forest community. Species stably existing in the community with normal populations occupy all tiers. Species whose populations are regressive or invasive are present only in the forest stand or only in the undergrowth, respectively.

The quantitative participation of trees in the first layer determines the current structure of the community and reflects the pre-existing possibilities of populations. The composition of the second tier characterizes the direction of the reconstruction of the modern first tier in the near future, due to the replacement of dying old trees by younger ones, the presence of abundant viable undergrowth may indicate a more distant prospect for the development of the community.

With age, the requirements of an individual to the environment and resistance to its individual factors naturally and very significantly change. At different stages of ontogenesis, a change in habitats, a change in the type of nutrition, the nature of movement, and the general activity of organisms can occur. Often, age-related ecological differences within a species are much more pronounced than differences between species. Common frogs on land and their tadpoles in water bodies, caterpillars gnawing leaves and winged butterflies sucking nectar, sessile sea lilies and their planktonic doliolaria larvae are just different ontogenetic stages of the same species. Age differences in lifestyle often lead to the fact that individual functions are entirely performed at a certain stage of development. For example, many species of fully metamorphosed insects do not feed in the imaginal state. Growth and nutrition are carried out at the larval stages, while adults perform only the functions of settling and reproduction.

Age differences in the population significantly increase its ecological heterogeneity and, consequently, its resistance to the environment. The probability increases that in case of strong deviations of conditions from the norm, at least a part of viable individuals will remain in the population and it will be able to continue its existence. The age structure of populations has an adaptive character. It is formed on the basis of the biological properties of the species, but always also reflects the strength of the impact of environmental factors.

Age structure of populations in plants. In plants, the age structure of the cenopopulation, i.e., the population of a particular phytocenosis, is determined by the ratio of age groups. The absolute, or calendar, age of a plant and its age state are not identical concepts. Plants of the same calendar age can be in different age states. age, or ontogenetic state of the individual - this is the stage of its ontogeny, at which it is characterized by certain relations with the environment. Complete ontogeny, or the long life cycle of plants, includes all stages of the development of an individual - from the emergence of an embryo to its death or to the complete death of all generations of its vegetatively arisen offspring (Fig. 97).

Rice. 97. Age conditions of meadow fescue (A), Siberian cornflower (B):

R- seedlings; j- juvenile plants; im- immature; v- virginal; g 1- young generative; g2- middle-aged generative; g 3- old generative; ss - subsenile; s - senile

sprouts have a mixed diet due to the reserve substances of the seed and their own assimilation. These are small plants, which are characterized by the presence of germinal structures: cotyledons, a germinal root that has begun to grow, and, as a rule, a uniaxial shoot with small leaves, which often have a simpler shape than in adult plants.

Juvenile Plants are transitioning to self-feeding. They lack cotyledons, but the organization is still simple, often retaining uniaxiality and leaves of a different shape and smaller size than in adults.

Immature plants have characteristics and properties that are transitional from juvenile plants to adult vegetative ones. They often begin branching of the shoot, which leads to an increase in the photosynthetic apparatus.

At adult vegetative In plants, features of a life form typical of the species appear in the structure of underground and terrestrial organs, and the structure of the vegetative body fundamentally corresponds to the generative state, but the reproductive organs are still absent.

The transition of plants into the generative period is determined not only by the appearance of flowers and fruits, but also by a deep internal biochemical and physiological restructuring of the body. In the generative period, Colchicum splendid plants contain about twice as much colchamine and half as much colchicine as in young and old vegetative individuals; in sverbiga orientalis, the content of all forms of phosphorus compounds sharply increases, as well as the activity of catalase, the intensity of photosynthesis and transpiration; in the gillweed, the content of RNA increases by 2 times, and total nitrogen - by 5 times.

Young generative plants bloom, form fruits, the final shaping of adult structures occurs. In some years there may be breaks in flowering.

Middle age generative plants usually reach their greatest vigor, have the highest annual growth and seed production, and may also have a break in flowering. In this age state, clone-forming species often begin to show disintegration of individuals, clones appear.

old generative plants are characterized by a sharp decrease in reproductive function, a weakening of the processes of shoot and root formation. The processes of dying off begin to prevail over the processes of neoformation, and disintegration intensifies.

Old vegetative (subsenile) plants are characterized by the cessation of fruiting, a decrease in power, an increase in destructive processes, a weakening of the connection between shoot and root systems, a simplification of the life form is possible, the appearance of leaves of an immature type.

Senile plants characterized by extreme decrepitude, a decrease in size, few buds are realized during renewal, some juvenile features appear again (the shape of the leaves, the nature of the shoots, etc.).

Dying individuals - an extreme degree of expression of the senile state, when only some tissues remain alive in the plant and, in some cases, dormant buds that cannot develop above-ground shoots.

In some trees (pedunculate oak, forest beech, field maple, etc.) quasi-senile age state (the term was proposed by T. A. Rabotnov). These are oppressed, stunted plants, described as stick-ups (Fig. 98). They acquire over time the features of an old vegetative plant, without going through the generative phase.

Rice. 98. Ontogeny of English oak in favorable conditions (above) and with a lack of light (according to O. V. Smirnova, 1998)

The distribution of individuals of a cenopopulation according to age conditions is called its age, or ontogenetic spectrum. It reflects the quantitative relationships of different age levels.

To determine the number of each age group in different species, different counting units are used. Separate individuals can be a counting unit if they remain spatially isolated during the entire ontogenesis (in annuals, tap-rooted mono- and polycarpic grasses, many trees and shrubs) or are clearly delimited parts of a clone. In long-rhizomatous and rhizomatous plants, partial shoots or partial bushes can be a counting unit, since, with the physical integrity of the underground sphere, they often turn out to be physiologically separated, which was established, for example, for May lily of the valley when using radioactive isotopes of phosphorus. In densely sod grasses (pike, fescue, feather grass, serpentine, etc.), along with young individuals, a compact clone can be a counting unit, which acts as a single whole in relations with the environment.

The number of seeds in the soil reserve, although this indicator is very important, is usually not taken into account when constructing the age spectrum of the cenopopulation, since their calculation is very laborious and it is almost impossible to obtain statistically reliable values.

If only seeds or young individuals are present in the age spectrum of the cenopopulation at the time of its observation, it is called invasive. Such a cenopopulation is not capable of self-maintenance, and its existence depends on the influx of rudiments from outside. Often this is a young cenopopulation that has just invaded the biocenosis. If the cenopopulation is represented by all or almost all age groups (some age states in specific species may not be expressed, for example, immature, subsenile, juvenile), then it is called normal. Such a population is independent and capable of self-maintenance by seed or vegetative means. It can be dominated by certain age groups. In this regard, young, middle-aged and old normal cenopopulations are distinguished.

A normal cenopopulation consisting of individuals of all age groups is called full member, and if there are no individuals of any age conditions (in unfavorable years, separate age groups may temporarily fall out), then the population is called normal incomplete.

regressive the cenopopulation is represented only by senile and subsenile or also generative, but old, not forming germinating seeds. Such a cenopopulation is not capable of self-maintenance and depends on the introduction of rudiments from outside.

An invasive cenopopulation can turn into a normal one, and a normal one can turn into a regressive one.

The age structure of the cenopopulation is largely determined by the biological characteristics of the species: the frequency of fruiting, the number of produced seeds and vegetative primordia, the ability of vegetative primordia to rejuvenate, the rate of transition of individuals from one age state to another, the ability to form clones, etc. A typical age spectrum is called basic(Fig. 99). The manifestation of all these biological features, in turn, depends on environmental conditions. The course of ontogenesis also changes, which can occur in one species in many variants (polyvariance of ontogenesis), which affects the structure of the age spectrum of the cenopopulation (Fig. 100).

Rice. 99. The basic type of the spectrum of coenopopulations (according to L. B. Zaugolyyuva, 1976) A - Lensky beetroot; B - leafless anabasis; B - meadow fescue; G - tipchak.

1 - base spectrum; 2 - limits of change of the base spectrum

Different plant sizes reflect different vitality individuals within each age group. The vitality of an individual is manifested in the power of its vegetative and generative organs, which corresponds to the amount of accumulated energy, and in resistance to adverse effects, which is determined by the ability to regenerate. The vitality of each individual changes in ontogenesis along a single-peak curve, increasing on the ascending branch of ontogenesis and decreasing on the descending one. In many species, individuals of the same age state in the same cenopopulation may have different vitality. This differentiation of individuals in terms of vitality can be caused by the different quality of seeds, different periods of their germination, microenvironmental conditions, the impact of animals and humans, and competitive relations. High vitality can be maintained until the death of an individual in all age states or decrease in the course of ontogeny. Plants with a high level of vitality often go through all age states at an accelerated pace. In cenopopulations, plants of an average level of vitality often predominate. Some of them go through ontogenesis completely, while others skip part of the age states, passing to a lower level of vitality before dying off. Plants of the lowest level of vitality have a shortened ontogeny and often pass into the senile state as soon as they start flowering.

Rice. 100. Options for the development of the hedgehog team in different environmental conditions (according to L. A. Zhukova, 1985). Latin letters indicate the age states of plants, and dotted lines indicate their possible sequence.

Individuals of the same cenopopulation can develop and move from one age state to another at different rates. Compared with normal development, when age states replace each other in the usual sequence, there may be an acceleration or delay in development, the loss of individual age states or entire periods, the onset of secondary dormancy, some individuals may rejuvenate or die. Many meadow, forest, steppe species, when grown in nurseries or crops, that is, on the best agrotechnical background, reduce their ontogeny, for example, meadow fescue and cocksfoot - from 20-25 to 4 years, spring adonis - from 100 to 10 -15 years old, gillweed - from 10-18 to 2 years old. In other plants, when conditions improve, ontogeny can be lengthened, as, for example, in common cumin.

In dry years and with increased grazing in the steppe species of Shell's sheep, individual age states drop out. For example, adult vegetative individuals can immediately replenish the group of subsenile, less often old generative ones. Tuber-bulbous plants of Colchicum splendid in the central parts of compact clones, where conditions are less favorable (lighting, moisture, mineral nutrition are worse, the toxic effect of dead residues is manifested), quickly pass into a senile state than peripheral individuals. In Sverbiga orientalis, under increased grazing load, when the renewal buds are damaged, young and mature generative individuals may have interruptions in flowering, thereby rejuvenating themselves and prolonging their ontogeny.

Under different conditions, hedgehogs of the national team implement from 1-2 to 35 paths of ontogenesis, and in large plantain from 2-4 to 100. The ability to change the path of ontogenesis ensures adaptation to changing environmental conditions and expands the ecological niche of the species.

In two species of steppe sheep - Shell and pubescent - in the Penza region, a cyclic change in age spectra in the long-term dynamics is clearly traced. In dry years, sheep populations age, and in wet years they get younger. Fluctuations in the age spectrum of cenopopulations following weather conditions are especially characteristic of plants in floodplain meadows.

The age spectrum can vary not only due to external conditions, but also depending on the reactivity and stability of the species themselves. Plants have different resistance to grazing: in some, grazing causes rejuvenation, since the plants die off before reaching old age (for example, in plain wormwood), in others it contributes to the aging of the cenopopulation due to a decrease in renewal (for example, in the steppe species of Ledebour's gill).

In some species, throughout the range, in a wide range of conditions, normal cenopopulations retain the main features of the age structure (common ash, fescue, meadow fescue, etc.). This age spectrum depends mainly on the biological properties of the species. In it, first of all, the ratios are preserved in the adult, most stable part. The number of newly emerging and dying individuals in each age group is balanced, and the overall spectrum is constant until significant changes in the conditions of existence. Such basic spectra most often have cenopopulations of edificatory species in stable communities. They are contrasted with cenopopulations that relatively quickly change their age spectrum due to unstable relationships with the environment.

The larger the individual, the greater the scope and degree of its impact on the environment and on neighboring plants (“phytogenic field”, according to A. A. Uranov). If the age spectrum of the cenopopulation is dominated by adult vegetative, young and middle-aged generative individuals, then the entire population as a whole will occupy a stronger position among others.

Thus, not only the number, but also the age spectrum of the cenopopulation reflects its state and adaptability to changing environmental conditions and determines the position of the species in the biocenosis.

Age structure of animal populations. Depending on the characteristics of reproduction, members of a population may belong to the same generation or to different ones. In the first case, all individuals are close in age and approximately simultaneously go through the next stages of the life cycle. An example is the reproduction of many grasshopper species. In the spring, the first-stage larvae appear from the eggs that have overwintered in egg-pods laid in the ground. The hatching of larvae is somewhat extended under the influence of microclimatic and other conditions, but on the whole proceeds quite amicably. At this time, the population consists only of young insects. After 2-3 weeks, due to the uneven development of individual individuals, larvae of adjacent instars can simultaneously occur in it, but gradually the entire population passes into the imaginal state and by the end of summer consists only of adult sexually mature forms. By winter, laying eggs, they die. This is the same age structure of populations in the oak leafworm, slugs of the genus Deroceras, and other species with a one-year development cycle that breed once in a lifetime. The timing of reproduction and the passage of individual age stages are usually confined to a specific season of the year. The size of such populations is, as a rule, unstable: strong deviations of conditions from the optimum at any stage of the life cycle affect the entire population at once, causing significant mortality.

Species with the simultaneous existence of different generations can be divided into two groups: those that breed once in a lifetime and those that breed many times.

In May beetles, for example, the females die shortly after laying eggs in the spring. The larvae develop in the soil and pupate in the fourth year of life. At the same time, representatives of four generations are present in the population, each of which appears a year after the previous one. Every year one generation completes its life cycle and a new one appears. Age groups in such a population are separated by a clear interval. The ratio of their numbers depends on how favorable the conditions were for the appearance and development of the next generation. For example, the generation may be small if late frosts destroy some of the eggs or cold rainy weather interferes with the flight and copulation of the beetles.

Rice. 101. The ratio of age groups of herring for 14 years. "Productive" generations can be traced for several years (according to F. Schwerdpfeger, 1963)

In species with a single reproduction and short life cycles, several generations are replaced during the year. The simultaneous existence of different generations is due to the prolongation of oviposition, growth and sexual maturation of individual individuals. This occurs both as a result of the hereditary heterogeneity of the members of the population, and under the influence of microclimatic and other conditions. For example, beet moths, which damage sugar beets in the southern regions of the USSR, have caterpillars of different ages and pupae overwinter. During the summer, 4-5 generations develop. At the same time, representatives of two or even three adjacent generations meet, but one of them, the next in terms, always prevails.

Rice. 102. The age structure of animal populations (according to Yu. Odum, 1975; V. F. Osadchikh and E. A. Yablonskaya, 1968):

A - general scheme, B - laboratory populations of the vole Microtus agrestis, C - seasonal changes in the ratio of age groups of the mollusk Adaena vitrea in the North Caspian.

Different shading - different age groups:

1 - growing, 2 - stable, 3 - declining population

The age structure of populations in species with repeated reproduction is even more complicated (Fig. 101, 102). In this case, two extreme situations are possible: 1) life expectancy in the adult state is small and 2) adults live long and multiply many times. In the first case, a significant part of the population is replaced annually. Its number is unstable and can change dramatically in individual years, favorable or unfavorable for the next generation. The age structure of the population varies greatly.

In the root vole, the age structure of the population over the summer season gradually becomes more complex. At first, the population consists only of individuals of the last year of birth, then the young of the first and second litters are added. By the period of the appearance of the third and fourth offspring, puberty occurs in representatives of the first two, and generations of the grandchild generation join the population. In autumn, the population consists mainly of individuals of the current year of birth of different ages, since the older ones die.

In the second case, a relatively stable population structure arises, with long-term coexistence of different generations. So, Indian elephants reach sexual maturity by 8-12 years and live up to 60-70 years. The female gives birth to one, less often two elephants, about once every four years. In a herd, usually adult animals of different ages make up about 80%, young animals - about 20%. In species with higher fecundity, the ratio of age groups may be different, but the general structure of the population always remains quite complex, including representatives of different generations and their offspring of different ages. Fluctuations in the number of such species occur within small limits.

The long-term breeding part of a population is often referred to as reserve. The possibility of population recovery depends on the size of the population reserve. That part of the young that reach puberty and increase the stock is the annual replenishment populations. In species with the simultaneous existence of only one generation, the reserve is practically equal to zero and reproduction is carried out entirely due to replenishment. Species with a complex age structure are characterized by a significant stock size and a small but stable recruitment rate.

When human exploitation of natural populations of animals, taking into account their age structure is of paramount importance (Fig. 103). In species with a large annual recruitment, a larger part of the population can be removed without the threat of undermining its numbers. If, however, many adults are destroyed in a population with a complex age structure, then this will greatly slow down its recovery. For example, in pink salmon, which matures in the second year of life, it is possible to catch up to 50-60% of spawning individuals without the threat of further population decline. For chum salmon that matures later and has a more complex age structure, the removal rates from a mature herd should be lower.

Rice. 103. Age structure of the Taimyr population of wild reindeer during the period of moderate (A) and excessive (B) hunting (according to A. A. Kolpashchikov, 2000)

Analysis of the age structure helps to predict the size of the population over the life of a number of next generations. Such analyzes are widely used, for example, in the fish industry to predict the dynamics of commercial stocks. They use rather complex mathematical models with a quantitative expression of the impact on individual age groups of all environmental factors that can be accounted for. If the selected indicators of the age structure correctly reflect the real impact of the environment on the natural population, highly reliable forecasts are obtained that allow planning the catch for a number of years in advance.