Characteristic features of r and k species. Plant Ecological Strategies

How to determine the value of an individual for a population?

« Natural selection recognizes only one kind of "currency" - prosperous offspring"(E. Pianka, 1981).

We have said that a population is a potentially immortal entity made up of mortal individuals. In order to maintain the existence of a population, an individual must survive on its own and leave descendants who can also survive. Pay attention to the duality of this task. Probably, the individual that will not spend resources and the energy obtained from them on the production of offspring will have the greatest chance of survival. But a little time will pass - and such an individual will disappear from the population without a trace. At the opposite "pole" is a hypothetical individual, which, immediately after its appearance, begins to direct all its energy to the production of offspring. Such a creature will die on its own and, if its offspring inherit an equally inefficient way of allocating resources, will produce offspring that will have no chance of surviving.

This means that the individual that combines the costs of its own survival and the production of offspring in an optimal combination should have the greatest value for the population. It is possible to evaluate how this combination is optimal. To do this, it is necessary to calculate at what combination, under given conditions, the individual will leave the greatest possible contribution to the future generation. The measure that is used for this in mathematical population biology is called reproductive value. Reproductive value is a generalized measure of survival and fertility, taking into account the relative contribution of an organism to future generations.

« It is easy to describe a hypothetical organism that has all the traits necessary to achieve high reproductive value. He breeds almost immediately after birth, gives numerous, large, protected offspring, which he takes care of; it reproduces many times and often over a long life; he wins in competition, avoids predators and easily obtains food. It is easy to describe such a creature, but it is difficult to imagine....” (Bigon et al., 1989).

You understand that such an impossibility follows from the inconsistency of the tasks of self-maintenance and reproduction (Fig. 4.15.1). One of the first to realize this in 1870 was the English philosopher Herbert Spencer, who spoke of the alternative of maintaining an organism's own existence and continuing itself in descendants. In modern language, we can say that these parameters are connected by negative correlations, the ratio in which the improvement of the system in one parameter must be accompanied by its deterioration in another.

Rice. 4.15.1. At the rotifer Asplanchna chances of survival decrease as fertility increases (Pianka, 1981)

Different species (and different populations) redistribute energy between self-maintenance and reproduction in different ways. We can talk about a species strategy, which is expressed in how the representatives of the species extract resources and how they spend them. A successful strategy can only be one in which individuals receive enough energy so that they can grow, reproduce and compensate for all losses to predator activity and various misfortunes.

Features related to different adaptive strategies can be related by the relation tradeoff, that is, irresistible negative correlations (either-or relation). Thus, the tradeoff ratio relates to the number of offspring and their survival rate, growth rate and resistance to stress, etc. American ecologists R. MacArthur and E. Wilson described in 1967 two types of species strategies that are the result of two different types of selection and are related by the tradeoff relation. The accepted designations of these strategies (r- and K-) are taken from the logistic equation.

According to the logistic model, two phases can be distinguished in population growth: with accelerating and decelerating growth (Fig. 4.15.2). Bye N is small, the population growth is mainly influenced by the factor rN and population growth is accelerating. At this phase ( r-phase) population growth is accelerating, and its number is higher, the higher the ability of individuals to reproduce. When N becomes sufficiently high, the factor (K-N)/K. At this phase ( K-phase) population growth is slowing down. When N=K, (K-N)/K=0 and the population growth stops. In the K-phase, the population size is the higher, the higher the parameter K. It is the higher, the more competitive individuals are.

Rice. 4.15.2. r- and K-phases of population growth in accordance with the logistic model

It can be assumed that the populations of some species are in the r-phase most of the time. In such species, individuals that can rapidly multiply and capture an empty environment with their descendants have the maximum reproductive value. In other words, at this phase, selection will increase the parameter r- reproductive potential. This selection is called r-selection, and the resulting species - r-strategists.

In species whose populations are in the K-phase most of the time, the situation is quite different. The maximum reproductive value in these populations will be inherent in individuals that will be so competitive that they can get their share of the resource even in conditions of its scarcity; only then will they be able to reproduce and contribute to the next generation. A population consisting of such individuals will have more high value parameter K- the capacity of the environment than one that consists of individuals that are not "able" to fight for the missing resources. At this stage, K-selection acts on the population, the result of which is the appearance of species - K-strategists. K-selection is aimed at increasing the cost of developing each individual and increasing its competitiveness.

Transitions between these strategies are possible, but they are intermediate, and do not combine the typical expressions of the two forms.

« You can't be a lettuce and a cactus at the same time"(E. Pianka).

Important for determining which selection (r- or K-) will act on a species is the dynamics of changes in the amount of available resource and the severity of competition for it. With a sharp indiscriminate reduction in the number of populations caused by a lack of a resource due to external reasons, r-strategists gain an advantage, and in the case of competition for the missing resource, K-strategists.

The choice between r-strategy (increasing fertility) and K-strategy (increasing competitiveness) seems to be quite simple, but it affects many parameters of organisms and their life cycles. Let's compare these strategies in their typical form (Table 4.15.1).

Table 4.15.1. Features of r- and K-selection and strategies

Characteristics	r-selection and r-strategists	K-selection and K-strategies
	changeable, unpredictable	Constant, predictable
Mortality	Catastrophic, independent of population density	induced by competition, dependent on population density
Mortality Curve	Usually type III	Usually type I or II
Population size	Changeable, unbalanced	Constant, close to the limiting capacity of the medium
Free resources	The emergence of free resources, filling the "environmental vacuum"	There are almost no free resources, they are occupied by competitors
Intra- and interspecific competition
body size	Relatively small	Relatively large
Development		Slow
Maturity
Reproduction rate
Reproduction throughout life	Often once	repeated
Offspring in the brood		Few, often alone
Amount of resource per child
Lifespan	short
fixtures	Primitive	Perfect
Optimized	Productivity	Efficiency

It may be surprising why r-strategists are characterized by a single reproduction, while K-strategists - repeatedly. This feature is easier to explain with an example. Imagine mice populating a barn with grain (plenty of resource, no competition). Consider two types of strategies.

View number 1. Sexual maturity at 3 months, the number of offspring in the brood is 10, the female lives for a year and is able to breed every three months.

View number 2. Sexual maturity at 3 months, the number of offspring in the brood is 15, having fed them, the female dies of exhaustion.

In the first case, after three months, 10 offspring and their parents will start breeding (12 heads in total), and in the second, as many as 15 offspring. The second type can provide a higher rate of capturing free resources. The typical r-strategy forces individuals to breed as early and as hard as possible, and therefore r-strategies are often limited to a single breeding season.

On the other hand, it is easy to see why typical K-strategists multiply many times over. In a competitive environment, only that descendant will survive, for the development of which a lot of resources have been spent. On the other hand, in order to survive and reproduce, an adult must spend a significant amount of energy on its own maintenance and development. Therefore, in the limiting case, K-strategists produce one child at a time (as do elephants and whales, and in most cases also humans). But no matter how perfect these animals are, a pair of parents will eventually die. In order for the population not to stop, a pair of parents must leave a pair of surviving offspring, and, therefore, must give birth to more than two. If so, a necessary condition for the survival of K-strategists is the multiplicity of reproduction of their constituent individuals.

In 1935, the Soviet botanist L.G. Ramensky singled out three groups of plants, which he called coenotypes (the concept of strategies had not yet been formed): violents, patients, and explerents. In 1979, these same groups (under other names) were rediscovered by the English ecologist J. Grime (Fig. 4.15.3). These strategies are.

Rice. 4.15.3. "Grime Triangle" - classification of specific strategies

- Type C (competitor, competitor) violet according to Ramensky; spends most energy to sustain the life of adult organisms dominates in stable communities. Among plants, trees, shrubs or powerful grasses (for example, oak, reed) most often belong to this type.

- Type S (stress-tolerant, stress tolerance); patient according to Ramensky; thanks to special adaptations it endures adverse conditions; uses resources where almost no one competes with him for them. Usually these are slow growing organisms (for example, sphagnum, lichens).

- Type R(from lat. ruderis, ruderal), explerent according to Ramensky; replaces violets in destroyed communities or uses resources temporarily unclaimed by other species. Among plants, these are annuals or biennials that produce many seeds. Such seeds form a seed bank in the soil or are capable of spreading efficiently over considerable distances (eg, dandelion, fireweed). This allows such plants to wait for the release of resources or capture free areas in time.

Many species are able to combine different types of strategies. Pine is categorized as CS as it grows well on poor sandy soils. Nettle is a CR strategist as it dominates disturbed habitats.

The species strategy can be plastic. Pedunculate oak - violet in the zone deciduous forests and a patient in southern steppe. The Japanese technology of bonsai (growing bonsai in pots) can be presented as a way to turn violets into patients.

An interesting task is to compare the MacArthur–Wilson and Ramensky–Grim strategies. It is clear that R-type organisms, explerents, correspond to r-strategists. But K-strategists correspond not only to C-type organisms, violets, but also to those who belong to S-type, patients. Violents maximize their competitiveness (and the capacity of the environment) under conditions of intense competition for resources favorable for consumption, while patients maximize their competitiveness under conditions of difficult resource consumption. In other words, the tasks that an oak, competing for light in a dense forest, and a fern, surviving in dim light in the depths of a cave, have much in common: the need to optimize resource consumption and improve individual fitness of an individual.

Story development of the concept of "ecological strategy" in plants .

Firstly, the term "strategy" meant a set of properties that help organisms survive in given conditions, and was applied only to animal organisms.

R- and K-strategies were distinguished according to the ratio of the costs of reproduction and maintenance of offspring.

K-strategists are distinguished by concern for a small number of offspring, this is observed, for example, in elephants. R-strategists are characterized by maximum fecundity and lack of care for offspring, for example, roundworms.

Properties K- andRstrategies in animals.

R-strategy	K-strategy
Characterized by the rapid development of individuals	Characterized by slow development
High fertility	Low fertility
Small sizes of individuals	Large sizes of individuals
Short lifespan	Significant life expectancy
Earlier acts of reproduction	late breeding
All signs are aimed at higher productivity	All signs are aimed at the most efficient use of resources
It is typical for catastrophic changes in the environment, during the settlement of unfilled biotopes.	Most effective in a competitive environment.

Later, the term "ecological strategy" began to be used in relation to plant organisms. (20).

For domestic literature, the term "strategy" in relation to plants is quite new and was the first to be used by T.A. Rabotnov (1975), who named the isolated L.G. Ramensky (1936) "coenobiotic types".

Under the strategy of a species, Rabotnov proposed to understand "a set of adaptations that provide it with the opportunity to live together with other organisms and occupy a certain place in the corresponding biogeocenosis." (10)

As early as 1894, McLeod was the first to point out the presence of prerequisites for plants that determine their status in the community, and he divided all species into “capitalists” and “proletarians”.

However, both the analogy with society itself and the main criterion for distinguishing types - cross-pollination and self-pollination, were unsuccessful, although the scientist tried to make the assessments comprehensive and wrote that "capitalists" are characterized by the presence of a reserve nutrients, polycarpicity, intolerance to shading, etc.

This issue was brilliantly developed in the works of Ramensky, published in the 30s, where he wrote about 3 types of plants, which he called violents, patients and explerents and likened them to lions, camels and jackals.

After 40 years, a monograph by J. Grime "Plant strategies and processes in vegetation" was published in England. , in which the author, not knowing the works of Ramensky, re-described the same three types of strategies under the names of competitors, stress-tolerants and ruderals.

To understand the type of strategies, much has also been done by E. Pianka, R. Whittaker and T.A. Rabotnov. (11)

The main systems of ecological and cenotic strategies .

E. Pianka's system.

Pianka's system, which is the most widely used in ecology, includes two types of strategies associated with K-selections and r-selections (according to the ratio of the shares of energy costs for maintaining adults and for reproduction processes).

K-selection is selection in a constant (predictable) environment, where the main part of the population's energy is spent on competition, and with r-selection, reproduction is the main energy expenditure item.

The system was the result of the development of ideas that were formulated earlier by R.Kh. MacArthur and E.O. Wilson, but it was E. Pianka who comprehensively analyzed the consequences that arise as a result of the implementation of two types of selection.

The two types of Pianka strategy are the most widespread in the plant world. And even the emergence of heterospores in club mosses or ferns can ultimately be considered as a replacement of the r-strategy of isospores with the K-strategy of the female gametophyte, which guarantees better survival of the offspring and replaces a huge number of small isospores with a limited number of megaspores that provide the necessary conditions for the development of a female outgrowth.

K-strategists are confined to more or less stable environmental conditions, have equilibrium populations, where mortality is regulated by density, and are adapted to conditions of intense competition. They tend to be polycarpic with slow development and a life form ranging from herbs to trees. In successional series, these species increase their participation as the successional stage approaches the climax.

r-strategists, on the other hand, prefer unstable habitats characterized by non-equilibrium populations, whose mortality does not depend or only slightly depends on density. The competition between such plants is weak, these are juvenile monocarpics, usually grasses, less often shrubs. In the successional series, they are associated with the pioneer stages and do not play a significant role in mature communities preceding the climax.

Thus, E. Pianka's type system is simple - one-dimensional, but it fully corresponds to the continuum perception of types.

He notes the relativity of dividing all types into 2 types of strategies, emphasizing that the world is not painted only in black and white, and extreme options, as a rule, are connected by a whole range of transitions (E. Pianka, 1981, p. 138). (13)

R. Whittaker's system.

R. Whittaker (1980) distinguished not 2, but three types of strategies, denoted letters K, r and L. His system is based on the patterns of fluctuations in the number of populations between two limits: K-upper limit, corresponding to the maximum saturation density and L-lower limit, meaning a certain “population zero”, corresponding to a population that is not able to ensure the survival of the population.

K-strategists strive to achieve the level of K, achieving this, firstly, by limiting niche differentiation. K-selection affects the mechanisms by which they maintain their population in the process of competition and other interactions within the boundaries of the environment they occupy. The number of populations is significantly reduced, but the general trend of such populations is fluctuations around the level of K.

The second group of populations_r-strategists. They are characterized by sharp fluctuations between the levels of K and L. Such populations are unstable and survive only due to the high rate of production of diaspores, they are poorly adapted both to conditions of increased competition and to unfavorable conditions that cause stress.

The third group of populations are L-strategists, which fluctuate around the lower limit of abundance L, although they can at times increase their abundance explosively. In such populations, selection tends to improve the mechanism for surviving adverse periods, and the rate of reproduction may or may not be high.

Distinguishing three types of selection with their result - three primary types, at the same time, Whittaker, like Pianka, did not make his system absolute.

If we compare Whittaker's and Pianka's systems, it is obvious that his types K and r correspond to Pianka's K and r, and niche differentiation is indeed under the influence of K-selection. These are mainly perennial species, often propagating vegetatively, and consuming relatively little energy in the generative sphere.

Ruderal plants, on the other hand, are shorter life cycle and high seed productivity, and therefore the cost of reproduction is higher here. This is a consequence of r-selection.

Group L occupies a transitional position, since desert annuals are among the ephemerals with a very fast development cycle and high seed production (result of r-selection), but shrubs, as well as some herbaceous turf plants, experience stress in the vegetative state and therefore represent the result of K-selection. (10)

Ramensky-Grime system.

Ramensky proposed a system of three types. He distinguished three "coenobiotic types".

The first type, which he called "violents" or "lions", is characterized by the ability to vigorously seize territory, the fullness of the resources used, and powerful competitive suppression of rivals.

The second type - patients or "camels" are distinguished by their ability to endure extreme environmental conditions, that is, endurance.

The third type - explerents or jackals are neither resistant to stressful situations nor high competitive power, but are capable of quickly capturing gaps between stronger plants, and when they close, they are also easily forced out. (13)

In the future, the representations and classification of L.G. Ramensky (1935-38) were developed by T.A. Rabotnov. (1966, 1975, 1978, 1980). He showed the complex nature of patient (stress tolerance) in plants and identified ecological and phytocenotic patients.

The former are able to exist in unfavorable conditions due to ecological specialization (on saline, acidic, dry or stony substrates, etc.) and are most consistent with L.G. Ramensky. They have the same autecological and synecological optima.

The latter are able to survive for a long time under the pressure of violets in ecologically optimal conditions with the help of a maximum reduction in vital processes. Synecological and autecological optima usually do not coincide with them. (6 )

We find further development of ideas about the types of strategies in the numerous works of J. Grime (J. Grime, 1974, 1978, 1979).

He offers, in essence, 3, the same as those of L.G. Ramensky, the type of ecological-coenotic strategies, calling these types: competitors, stress tolerants and ruderals (respectively K, S and R).

The most strikingly opposite strategies of social contacts are manifested, of course, in reproductive behavior, i.e. in the breeding strategy.

In most species, including humans, both reproductive strategies occur. The general direction of human evolution can be described as a movement from r-strategy to K- strategies. You can even specify an approximate time when K- strategy began to prevail - this is the III millennium BC, when the myth of the conflict between Niobe and Latona arose on the territory of Asia Minor.

Niobe refused to offer sacrifices to Latona and her children by Zeus to Apollo and Artemis. She explained this, in particular, by the fact that she has seven times more children than Latona. Offended, Latona complained to the children. Apollo and Artemis, who stood up for their mother, killed all the Niobids with arrows.

The biological meaning of this myth is obvious: it is better to have few descendants, but more adapted to environment, which in competition will win over more numerous, but worse adapted individuals. And the great adaptive capabilities of the offspring are achieved, as already noted, firstly, by a careful choice of a reproductive partner and, secondly, by careful care for the offspring - what a person calls upbringing and training.

In human evolution r-strategy is being phased out TO-strategy.

The evolutionary advantage has shifted to K- strategists, i.e. a greater number of reproductively successful offspring began to be left by those women who: 1) carefully chose their reproductive partner (spouse) and 2) had pronounced parental behavior, i.e. provide children with careful care, educate and educate them.

Woman K- the strategist is interested in the fact that the reproductive partner spends all the extracted resources on providing only her offspring.

Despite the fact that, in general, a person is a monogamous species (more precisely, among people there are more representatives K-strategy), often there are carriers of the opposite strategy of reproduction, quite indifferent to their children. Such people, especially women, often painfully experience their indifference, considering themselves to blame for the lack of parental feelings. Doctors distinguish this condition as a special neurosis of the “bad mother”.

The type of reproductive strategy to which a person belongs is revealed only after the birth of a child. Then the hormonal reaction that accompanies childbirth initiates a complex of parental behavior. It is difficult to determine the belonging of a woman to one or another psychological type before childbirth. -r- or TO- strategies. It is impossible to bring up attention to one's own children.

The coldness or hostility of a woman towards her children are variants of the norm. This is the extreme r- breeding strategies.

If a healthy woman has high level cortisol at rest, i.e. it belongs to the psychological type B, then this serves as the basis for predicting intensive parental behavior. The concentration of cortisol in the blood during pregnancy increases in all women. But its increase is greater in those women who subsequently showed more pronounced maternal behavior.

In addition to cortisol, the propensity for parental affiliation is reflected in the ratio of estradiol to progesterone. A gradual increase in this ratio from early to late pregnancy is a marker TO- strategies.

Regarding the hormonal regulation of paternal behavior, i.e. parental behavior of men, very little is known. There is evidence that parental behavior is more pronounced in men with low testosterone levels and high prolactin levels. Men who spend a lot of time with their children under 1 year of age have higher levels of cortisol and prolactin in the blood than those who spend little time on such communication, but the differences do not reach the level of statistical significance.

Practical value biological marker studies K-strategy is obvious. A woman makes different, in many ways opposite demands on her sexual and reproductive partner. If a lover should possess the maximum number advantages, then the husband should have a minimum number of shortcomings. And only two positive qualities: to bring money and treat children well. Therefore, the problem of choosing a spouse will be greatly facilitated when concrete biological signs of a person’s propensity for behavior that provide K- breeding strategy. Unfortunately, this problem is still far from being solved.

It should be noted that the behavior characteristic of the two breeding strategies is manifested not only in relations with children and spouses. Reproductive behavior strategies are a special case of social contact strategies.

Choose - me or this cat!

Well, I choose you. Still, I have known you for a long time, and this is the first time I see this cat.

E. Uspensky

The character of E. Uspensky is obvious K- strategist, because in case of need for an alternative choice, he prefers a well-known person. The owner of the opposite psychological type will choose a stranger, since communication with him promises new experiences, it is more interesting with him.

r- And K- breeding strategies are a special case r- and K-strategies of social contacts.

r- And K-strategies of social contacts can be considered as psychological types. Type B animals actively respond with behavior and endocrine responses to the behavior of another animal. Rats of type A are indifferent to the behavior of their neighbor. Differences in the oxytocin system of these animals are very indicative. In animals of type A, the activity of the oxytocin system is two times lower than in animals of type B. Thus, there is a correspondence to the differences in humoral mechanisms and types of social contacts in animals of genetically selected lines.

Consider a few examples of the effect of oxytocin on human behavior.

Volunteers were injected intranasally with oxytocin, which increased trust between people.

Moreover, early social stress caused by separation from the mother leads to altered levels of oxytocin in adults. For example, in rhesus monkeys raised in isolation from their mothers, at the age of 18, 24, and 36 months, the number of affiliative social contacts, including the duration of allogrooming, is dramatically reduced, and the number of agonistic contacts and the duration of stereotyped motor acts are increased. In such isolates, the concentration of oxytocin in the cerebrospinal fluid is significantly lower than in normal ones; raised with mother monkeys.

Similar results were obtained in the study of people with a lack of contact with parents. Children who have been deprived of maternal care since birth, as adults, suffer from emotional disorders and show impaired social behavior. They also showed reduced activity of the oxytocin and vasopressin systems 147 . Disturbances in the oxytocin system have also been noted in children deprived of paternal presence, too. As you know, children of single mothers have an increased risk of emotional disorders. In adult men who grew up without a father, the inhibitory effect of intranasally administered oxytocin on the stress rise in blood cortisol is weakened.

Summing up the discussion of the issue of strategies for human social contacts, it should be said that, undoubtedly, there are two such strategies: r- And TO-. They manifest themselves primarily in relations with children, but also in all other social contacts. K- strategy is associated with high activity of the oxytocin system in the body, and r - with low activity. These two behaviors are genetically determined but can be altered, at least temporarily, by manipulating the body's oxytocin levels.

Reproduction - the production of offspring in any way available to the body.

biological sense

The biological meaning of reproduction and related processes is quite diverse. These are: firstly, the reproduction of the number of species and its increase, as opposed to natural mortality, being eaten by predators and other troubles. Secondly, it is the provision of new genetic combinations and the possibility of the appearance of new traits in offspring, which makes it possible evolutionary development groups. In addition, in the course of reproduction, the problem of spatial distribution is often solved (especially for sedentary species), experiencing a period of unfavorable conditions (most often at the stage of resting eggs), and access to new food resources (available only to juveniles or larvae, but not to adult organisms) can occur.

Problems and adaptations.

Only a few organisms, mostly primitive ones, are able to reproduce passively (for example, when they are torn apart). In addition, a similar method (asexual, it is vegetative reproduction) does not provide one of the main functions - the emergence of new traits in the offspring, which could provide material for further evolution. Therefore, as a rule, the main thing for animals is sexual reproduction. It requires: the development of special organ systems for the maturation of germ cells, ensuring the mating of these cells (male and female) from different individuals, providing these cells with nutrition for the development and growth of the embryo, and often also further care for juveniles until they gain independence.

There are at least a few different difficult moments. First, sedentary (especially attached) organisms must somehow solve the problem of finding a partner and mating (at first glance, practically unsolvable, especially at a low population density). Secondly, the juveniles that appear during reproduction in any case are very different from adults - they are many times smaller, which requires the development of new life strategies (other feeding mechanisms, protection from predators, osmoregulation, etc.). Finally, it is necessary to solve issues related to the growth of juveniles - that is, to specially design all structures, including skeletal ones, in such a way that they can grow more or less continuously, ultimately increasing many times over. However, it is clear that animals managed to successfully solve all these problems, and rather the mechanisms for their solution differ.

K- and R-breeding strategies

Reproduction strategies and offspring care have become the subject of one of the general ecological theories - the theory of R- and K-strategies. It is believed that all organisms gravitate toward one of these two reproductive strategies. K-strategists (usually large animals that dominate stable habitats and established communities, such as elephants) breed slowly and produce few but large offspring who are surrounded by attention and care. On the contrary, R-strategists (generally small animals of disturbed habitats, for example, rats) breed quickly and in large numbers, but care little for offspring, which is accompanied by high infant mortality (adult mortality is also high). The K-strategy is more beneficial under conditions where the well-being of the population is determined mainly by competition, and the R-strategy is more beneficial under the strong influence of hard . In humans, different strategies are manifested even within the species: in urban populations (especially in economically developed countries) people multiply slowly (barely ensuring reproduction), but invest a lot of money in the maintenance, upbringing and education of children. On the contrary, in the poor agrarian countries of the tropics, people multiply rapidly and actively, without the means to adequately clothe, shoe, educate and sometimes even feed children, which often leads to high infant mortality, but can also be accompanied by sharp outbreaks of numbers (which, by the way, partly keep the standard of living low in these countries).

This whole theory, however, was developed mainly for terrestrial vertebrates (and partly for terrestrial higher plants). In the environment of aquatic invertebrates, somewhat different patterns operate. Most often (especially in the sea) the opposite happens - large and massive organisms throw out millions of microscopic settling eggs or larvae; small hydrobionts settle themselves, and produce much fewer offspring. Let's explain this with examples.

Comparative overview of the reproduction of different taxa

Unicellular algae. In each group of unicellular algae, there are two types of reproduction - vegetative and sexual. Vegetative - cell division as a result of mitosis. When resources are provided, the cells of unicellular algae reproduce predominantly vegetatively, and the population increases exponentially. Under unfavorable conditions for vegetative division or as a result of other reasons, algae undergo sexual reproduction (meiosis), in which male and female gametes are formed, after the fusion of which a cell with a “new” genotype is formed. The life cycles of unicellular algae belonging to different phylogenetic groups differ. The cycles of many algae include resting stages - (resting cells, spores, cysts, etc.) for experiencing adverse conditions.

Invertebrates. The original (for aquatic, primarily marine invertebrates) type of reproduction is believed to be as follows. At about the same time, all adult males and females in in large numbers they sweep their reproductive products (eggs and spermatozoa) directly into the water, which themselves (if you're lucky) find each other in the water column and mate. This is called external fertilization. The body itself can be inactive or sedentary. A microscopic planktonic larva grows from a fertilized zygote, which swims in the water column for quite a long time, settling with currents, undergoing various transformations and eventually switching to external nutrition (most often phytoplankton - the so-called planktotrophic larva). Growing up and getting ready to move on to an adult lifestyle, the larva settles on a suitable bottom substrate and acquires signs of an adult individual, reaches macroscopic sizes, and then grows for a long time. This type of reproduction and development makes it possible to solve all the problems of settling and intraspecific competition precisely at the expense of larvae (and adults can even be sessile - they do not need to meet each other directly). On the other hand, such an approach is accompanied by enormous mortality both among gametes and among larvae, which requires their massive accumulation and release, and the synchronization of maturation and release of germ cells in different individuals of the population is extremely important. This is achieved by the release of signaling substances into the water, which stimulates the release of all pre-accumulated gametes into the water in individuals. Usually mass spawning occurs once a year, and in many organisms - once in a lifetime. As is easy to understand, such a strategy is convenient for relatively large, massive, massive, and inactive organisms: polyps, sponges, mollusks, large polychaetes, echinoderms, and crustaceans. In general, at sea, this option is considered the most typical.

And also small and mobile invertebrates (cladocerans and copepods, some small polychaetes, oligochaetes, snails) cannot afford a massive release of gametes into the water (simply not having enough mass), and use internal fertilization: they find each other and mate themselves, after which the female, as a rule, bears for some time developing eggs within themselves (reducing their mortality). Either passive eggs protected by a special shell or already active larvae are born. Larvae most often lead a lifestyle similar to adults; but often more mobile, which provides populations with better distribution in space. Sometimes, in this case, too, the larvae of benthic organisms become planktonic for some time. Often (for example, in oligochaetes), there are no larvae at all, and juveniles are similar in structure and lifestyle to adults ( direct development). All this makes it possible to generate several orders of magnitude less reproductive products, reducing reproductive costs, and at the same time reproduce all year round, without worrying about spawning synchronization. Often, at birth, the larva is supplied with a supply of nutrients sufficient for the passage of its entire larval dispersal life, and does not feed at all (lecithotrophic larva).

In fresh waters, reproduction of the first type (with external fertilization and a long planktonic larval stage) is hampered by osmotic problems: osmoregulation of floating gametes and planktonic larvae has proved extremely inconvenient, and most even lower invertebrates use internal fertilization - and no additional planktonic larvae. As a rule, fairly large eggs are laid - in small numbers, but with a decent supply of nutrients, which allows the organism to be largely lecithotrophic and hatch, being already quite macroscopic and with a developed osmoregulation system. This is the path of freshwater worms, snails and most crustaceans. Copepods (like cyclops) still have a planktonic larva (nauplius), but relatively short-lived, in a series of successive molts quickly reaching the definitive (adult) appearance.

Insects, as a group as a whole, are terrestrial, and highly mobile precisely at the stage of an adult (imago), during development aquatic environment developed their own strategy of reproduction and life cycle. They left to the share of adults exactly the dispersal function (as well as mating and oviposition), and the larvae that live in the water (and usually much longer than the adults) are responsible for feeding, growth (and the accumulation of nutrients in the body), as well as experiencing in the water seasons that are unfavorable for life on land (mainly winters). Insect larvae already hatched from eggs are macroscopic, capable of self-feeding, and have a completely perfect system of freshwater (and sometimes brackish-water) osmoregulation. It is interesting that adults in some groups (mayflies, caddisflies, chironomids, part of stoneflies) do not feed at all and live for a very short time, and their synchronized departure from water bodies is used for successful reproduction. Thus, adult insects in non-insects are equated, functionally, with reproductive products (gametes) in many marine invertebrates.

In some groups of invertebrates (more often in fresh water than in marine) hermaphroditism - when both male and female reproductive organs and gametes are formed in each individual. For example, hermaphrodites are all lung snails (Pulmonata), oligochaetes, barnacles. When mating, the organism can act as both a male and a female, and often both at once (then mutual fertilization is observed). The biological meaning of hermaphroditism (that is, growing a double set of organs in each body) is not entirely clear. Sometimes (but apparently rarely) self-fertilization occurs - this partly violates the very idea of ​​\u200b\u200bsexual reproduction (since the organism interbreeds with itself), but it allows a single individual to give rise to a new population in a new place.

Even rarer than hermaphroditism, animals have asexual reproduction, in which the mothers actually clone themselves, giving birth to genetically exactly the same females. This situation is especially typical for periods of outbreaks in the abundance of small freshwater invertebrates - in particular, daphnia and rotifers in summer period. In any case, this is a temporary measure, sooner or later (usually in autumn) being replaced by normal sexual reproduction. However, in unicellular protozoa (as in plants), asexual reproduction is the most common thing, it is due to it that the main reproduction of species occurs.

Fish. As a rule, fish have external fertilization, however, carried out with personal meeting parent individuals (the female lays her eggs, and the male immediately pours her milk). Accordingly, fish spawn, usually quite small and in large quantities. The number of eggs averages several thousand, but varies greatly among different types: from 10-30 pieces (in sticklebacks) to 10-100 million (in tuna, cod and many other large marine fish). At the same time, the eggs carry a certain supply of nutrients, which allows already fully formed fry to hatch from the eggs, capable of swimming and feeding. The fish fry do not master any new environments, but they intercept the feeding spectrums that are usually inaccessible to adult fish: they can feed on zooplankton and meiobenthos. True, it is not clear whether the fish as a whole benefit greatly from this circumstance, or whether this is a necessary measure (since the fish fry are not able to eat anything else due to their small size).

Individual species of fish, however, have rather bizarre forms of reproduction and protection of offspring. The most famous are migratory fish that change their habitat for the sake of reproduction. Salmon and sturgeon in their adult state live in the seas, but spawn in rivers (where they originated), and their juveniles, adapted to freshwater osmoregulation, stay in rivers for some time and only then descend into the sea. At the same time, salmon show miracles of heroism, overcoming the rapids of mountain taiga rivers; and soon after spawning they die off - right in the rivers, sharply increasing their saprobity. It turns out that this is such a peculiar way to saturate the habitat of juveniles with organic matter. Another question is how effective it is.

The eel, on the contrary, swims to breed from the rivers in the Sargasso Sea, and for this, its European population overcomes (downstream) almost the entire Atlantic Ocean. Juveniles (again downstream, but in a different way) return to European rivers. It doesn't seem to make much sense. It is believed that eel's extra-long migrations reflect continental drift, during which the Atlantic gradually expands, and eels have to swim further and further into their native sea every million years.

Some groups of fish have moved to an explicit K-strategy, mainly through viviparity. At the same time, fertilization is internal, the number of offspring is much smaller, but they themselves are larger and more viable at the time they enter the water. The most famous example is the viviparous aquarium fish Peciliidae (guppies and other pecilia). All aquarists know that they are much easier to breed than any other fish. For example, sharks act in a similar way - they lay very few eggs (usually 5-30), but very large ones - in a whale shark up to 60 cm (!) In diameter, which allows very large fish to hatch from them.

Amphibians. Amphibians have internal fertilization and lay rather large eggs - and always in the water. Like insects, most amphibians are amphibious - that is, they breed in water and have aquatic fish-like larvae (tadpoles), although adult animals live on land for most of their lives. In general, here we can also talk about the interception of a new habitat and food resources by tadpoles - this is generally true, but in fact it reflects the global inferiority of the entire class - amphibians simply cannot do otherwise.

Crabs and caring for a woman. In many crustaceans, especially higher ones, the adults are so well protected by a chitinous shell that they cannot mate except immediately after the female has molted. Therefore, a male ready for mating must not only find a female of his own species, but also wait for her molt, which can happen, for example, in a few weeks. Moreover, it is necessary to wait nearby, and not look for a molting female - because during and after molting, animals become extremely vulnerable and try to molt in safe shelters (where they are difficult to find). Therefore, for example, in king crabs, adult males gather around themselves several females (harem) and “herd” them, mating with those who shed, and protecting them from being eaten (primarily by other females of their own harem). Such vital care for the female has little to do with the frivolous "courting" of vertebrates. The situation is further complicated by the fact that in the event of a molt of the male himself, he can also be immediately eaten by his females, so for molting he is forced to leave his harem and carefully hide.

Harpacticides and pedophilia. These small copepods have weak sexual dimorphism, and their interspecific differences are small; and age-related changes (from copepodite stages of juveniles to sexually mature ones) are hardly noticeable. But the mating instinct in males is very strong. Therefore, a male ready for mating, rummaging in the bottom silt in search of a sexual partner, does not show legibility and mates with almost anyone - with a female of his own species (if you're lucky!), or with a male, or with a copepodite (that is, a young individual), or with a crustacean of a completely different species. Sometimes their similar activity is mistaken for an attempt to eat a partner, but this is an attempt to copulate. In the state of mating, the crustaceans swim for quite a long time, and if a male is also in the position of the female, he can meanwhile also catch a partner for mating; sometimes quite long chains of individuals are obtained in this way, only a few of which actually mate.

Snails and group mating. Pulmonary freshwater snails are hermaphrodites, and in some of them sex determination during mating is directly determined by the position of the animal itself - approximately according to the principle "who is on top, that is the male." For example, river cups ( Ancylus fluviatilis) for mating, they simply crawl one on top of the other, and then the copulatory organs hang down. This situation does not prevent another cup from crawling on top and copulating with the one below, and so on. As a result, a stack of copulating individuals can form, of which the lowest acts only as a female, and the highest as a male, and all the rest work with both organ systems (unlike stupid harpacticids, which can only imitate such a situation). Then they all crawl away and lay eggs together.

Bonellia and sex determination by fate. In the sessile marine echiurida bonellia, the planktonic larva, leaving for open swimming, does not yet have a definite sex, but already has not only a resettlement, but also a sexual task - to search for a female. If the larva manages to find an adult female bonellia, it penetrates into it and develops into a male (who then lives inside the female for the rest of her life, fertilizing her). If it is not possible to find a female, the larva eventually settles to the bottom and becomes a female itself.

“... two American scientists, Robert MacArthur and Edward Wilson, created R-K theory selection. Theory of two different strategies reproduction of living beings.

The theory of two strategies turned out to be so successful that it is used in a number of sciences, recognized by almost everyone, and entered textbooks and teaching aids.

R-strategy is the birth per unit of time as possible more cubs.

Each of them can be practically not taken care of, and each cub has not very many chances to survive. A fly lays 5 million eggs - and what, she is very worried about the fate of these 5 million future little flies? Insects, crustaceans, and mollusks lay eggs in hundreds of thousands and millions. Fish that spawn “only” tens of thousands of eggs, especially frogs that spawn thousands of eggs, are simply ideal parents in comparison with simpler creatures. Of course, they do not care about their offspring in any way, but these more complex animals are forced to spawn more complex, larger eggs - and thereby spawn a smaller number of these eggs. Some species of fish are already trying to protect their hatched fish: they build nests for them, attack predators that have appeared. Some species even keep the fry in their own mouth, and there the fry are saved in case of danger.

These are already elements of the K-strategy: the birth of a small number of cubs, each of which is important and valuable. The more complex the species, the more valuable each individual life is for it, the fewer cubs dies between birth and death. The easier it is Living being, the less it needs to be taught and prepared for life, the faster it becomes an adult.

A mouse can give birth three times a year to ten mice. The birth of a mouse is very easy, and the babies become adults in three weeks. They can already take care of themselves, the mother kicks them out and is ready to give birth to new ones. If the mice do not die, the world will soon be filled with hordes of adult mice. In more complex animals - elephants, chimpanzees, elks, bison - cubs are born less, and they die less often.

But even in large complex animals, the physiological norm is mortality. 60-70% newborns. A female chimpanzee and an elephant gives birth 10-15 times in her life. 7, 10 or even 12 of these cubs will die before they become adults. The very 2 or 3 cubs that are necessary for the reproduction of the species will grow up and give a tribe themselves.

After catastrophes during volcanic explosions, after tsunamis, new islands and coasts are "captured" by living beings with R-strategy. But soon larger, more complex animals with a K-strategy begin to dominate. Evolution is in many ways a struggle not for survival, but for dominance.”

Burovsky A.M., Phenomenon of the brain. Secrets of 100 billion neurons, M., "Yauza"; "Eksmo", 2010, p. 77-79.