The concept of life strategies. Theory of r-K selection Survival of r and k 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 was in 1870. English philosopher Herbert Spencer, who spoke about the alternative of maintaining an organism's own existence and continuing itself in descendants. On 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 a higher value of the 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 conditioned external causes lack of resources, 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

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. More high speed the capture of free resources will be able to provide the second kind. 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, necessary condition 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 of the energy to maintain 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 endures adverse conditions; uses resources where almost no one competes with him for them. These are usually slow growing organisms (e.g. 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 able to effectively spread over a considerable distance (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 strategies. Pine is classified as CS because it grows well in 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 the 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) in conditions of intense competition for resources favorable for consumption, and patients - in conditions of difficult consumption of resources. 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.

“... two American scientists, Robert MacArthur and Edward Wilson, created a theory R-K 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.

Ecological strategies of populations

Whatever the adaptations of individuals to living together in a population, whatever the adaptations of a population to certain factors, they are all ultimately aimed at long-term survival and continuation of themselves in any conditions of existence. Among all the adaptations and features, a set of basic features can be distinguished, which are called ecological strategy. This general characteristics growth and reproduction of a given species, including the growth rate of individuals, the period they reach sexual maturity, the frequency of reproduction, the age limit, etc.

Ecological strategies are very diverse and although there are many transitions between them, two extreme types can be distinguished: r-strategy and K-strategy.

r-strategy– it is possessed by rapidly breeding species (r-species); it is characterized by selection for an increase in the rate of population growth during periods of low density. It is typical for populations in an environment with abrupt and unpredictable changes in conditions or in ephemeral, ᴛ.ᴇ. existing for a short time (drying puddles, water meadows, temporary streams)

The main features of r-species are: high fecundity, short regeneration time, high abundance, usually small size of individuals (plants have small seeds), short life span, high energy expenditure for reproduction, short habitats, low competitiveness. R-species quickly and in large numbers populate unoccupied territories, but, as a rule, soon - within the life of one or two generations - are replaced by K-species.

The r-species include bacteria, all annual plants(weeds) and insect pests (aphids, leaf beetles, stem pests, locust gregarious phase). From perennials - pioneer species: Ivan-chai, many cereals, wormwood, ephemeral plants, from tree species- willows, white and stone birch, aspen, chosenia, from conifers - larch; they appear first on disturbed lands: burned areas, mountain ranges, construction quarries, along roadsides.

K-strategy - species with a low reproduction rate and high survival (K-species) have this strategy; it determines the selection for increased survival at a high population density approaching the limit.

The main features of K-species: low fertility, significant life expectancy, large sizes of individuals and seeds, powerful root systems, high competitiveness, stability in the occupied territory, high specialization of lifestyle. The rate of reproduction of K-species decreases with approaching the limiting population density and rapidly increases at low density; parents take care of their offspring. K-species often become dominant biogeocenoses.

K-species include all predators, humans, relic insects (large tropical butterflies, incl. Far Eastern, relict barbel, stag beetle, ground beetles, etc.), solitary locust phase, almost all trees and shrubs. Most prominent representatives plants - all conifers, Mongolian oak, Manchurian walnut, hazel, maples, herbs, sedges.

Different populations use the same habitat in different ways; therefore, species of both types of strategy can simultaneously exist in it.

EXAMPLES. In the forests on the Gornotaiga ecological profile, in spring, before the leaves bloom on the trees, ephemeroids rush to bloom, bear fruit and finish the growing season: corydalis, Amur adonis, anemones, eastern violet (yellow). Under the canopy of the forest, the flowering of peonies, lilies, and black crow begins. In open areas in the dry oak forests of the southern slope, sheep's fescue and pink roseweed grow. Oak, fescue and other species are K-strategists, maryannik is r-strategy. 40 years ago, after a fire in the fir-broad-leaved forest type, parcels of aspen (r-species) were formed. Today, aspen leaves the forest stand, giving way to K-species: linden, oak, hornbeam, walnut, etc.

Any population of plants, animals and microorganisms is a perfect living system capable of self-regulation, restoration of its dynamic balance. But it does not exist in isolation, but together with populations of other species, forming biocenoses. For this reason, interpopulation mechanisms regulating the relationship between populations are also widespread in nature. different types. The biogeocenosis, consisting of many populations of different species, acts as a regulator of these relationships. In each of these populations, interactions between individuals occur, and each population has an impact on other populations and on the biogeocenosis as a whole, just as the biogeocenosis with its constituent populations has a direct impact on each specific population.

As I.I. Schmalhausen: "... In all biological systems there is always an interaction of different regulation cycles, leading to self-development of the system according to the given conditions of existence..."

When optimal ratios are reached, a more or less long stationary state (dynamic equilibrium) of a given system occurs under given conditions of existence. "... For a population, this means the establishment of a certain genetic structure, including, different forms balanced polymorphism. For a species, this means the establishment and maintenance of its more or less complex structure. … For biogeocenosis, this means the establishment and maintenance of its heterogeneous composition and the established relationships between the components. When the conditions of existence change, the stationary state is, of course, violated. There is a reassessment of the norm and variants, and, consequently, a new transformation, ᴛ.ᴇ. further self-development of these systems ... ". At the same time, the relationships between the links change in the biogeocenosis, and the genetic structure is being restructured in the populations.

Ecological strategies of populations - concept and types. Classification and features of the category "Ecological strategies of populations" 2017, 2018.

Populations of species in which fertility and mortality are highly dependent on the action external factors, rapidly changing their numbers. Periodic changes in population size are called population waves. In some cases, the number changes in thousands and millions of times. These populations rarely reach the number K and exist due to the high value of r. This way of reproducing populations is called r-strategy.

R-strategies: (Selection for the number of offspring)

1. High fertility

2. Short regeneration time

3. High strength

4. Usually small sizes of individuals (small seeds in plants)

5. Short life span, high energy costs for reproduction

6. Short duration of habitats

7. Low competitiveness

r-strategists (explerents) are characterized by low competitiveness, high fecundity, lack of care for offspring, rapid development and short life span. r-Strategists are figuratively called "jackals", because they are able to conquer the vacated ecological space in a short time.

Populations of species in which births and deaths depend to a large extent on their density (that is, on the characteristics of the population itself), in lesser degree depend on external factors. They maintain numbers close to the value of K, so the way to reproduce such populations is called the K-strategy.

K-strategy: (Selection for the quality of offspring)

1. low fertility

2. significant life expectancy

3. large sizes of individuals and seeds, powerful root systems

4. high competitiveness, stability in the occupied territory

5. high specialization lifestyle

6. care for offspring

K-strategists (violents) are characterized by high competitiveness, low fertility, care for offspring, long development and long life expectancy. K-Strategists are figuratively called "lions" because they are able to for a long time maintain ecological space.

In addition to the r-strategy and K-strategy, there is also an S-strategy. S-strategists (patients) inhabit habitats with adverse conditions life for most organisms, in which there is practically no competition. Therefore, S-strategists are figuratively called "camels". According to the low value of r, they are close to "lions" (violents), and according to the high value of K, they are close to "jackals" (explerents). In terms of the duration of development and life span, S-strategists can be similar to both r-strategists and K-strategists.

For large (global) human populations, at a certain stage, hyperbolic growth

Opening Heinz von Foerster(Science, 1960): the growth of the Earth's population from ancient times to the 1960s–1970s is described very simple equation and precise schedule hyperbole(R 2 = 0.996, for the period 1000 - 1970)

Proof that human growth is not an exponent: specific growth rate increases with population growth (through a decrease in mortality)

Causes of hyperbolic growth - in addition to the "usual" positive feedbacks of unlimited exponential growth of any population, in human society there are its additional "accelerators".

For any level of technological development, there is a strictly defined level of population ( conjecture by Simon Kuznets - Michael Kremer) the rate of technological growth proportional, on the one hand, to the available level of technological development(the wider the technological base, the more inventions can be made on its basis), and on the other hand, population(how more people the more potential inventors and innovators among them). It turns out a system of double positive feedback , which spins the flywheel of hyperbolic population growth in the world: technological growth - the growth of the Earth's carrying capacity - demographic growth - more potential inventors - the acceleration of technological growth - the accelerated growth of the Earth's carrying capacity - even faster demographic growth - the accelerated growth in the number of potential inventors - more faster technological growth - further acceleration of the growth of the Earth's carrying capacity, etc.

Due to the fact that population growth again and again exceeded the next carrier limit of the environment, set by the next jump in the growth of technologies, epidemics, wars, famines and other horrors periodically occurred during the period of hyperbolic growth (the so-called " Malthusian trap»).

But as the general saturation limit of the medium (K) was approached, reverse negative connections already inhibiting growth (women's literacy, family planning) through declining birth rates. Growth rates declined mainly due to a reduction in the birth rate (K-strategy), while before that they grew due to a decrease in mortality.

Strictly hyperbolic growth was observed in humanity from the Late Paleolithic (40 thousand years ago) only until 1970. This was followed by a period of declining growth rates, due to the general demographic transition, When social factors first, the death rate was reduced, and a little later, the birth rate was also reduced. The main factors were: medicine, social security and literacy. All this marked the transition of our global population from the r-strategy to the K-strategy: to grow, albeit small, but high-quality offspring. For people, this means, first of all, - educated, i.e. competitive. And it costs more. Yes, and having many children as in an agrarian society is no longer necessary.

Demographic transition- a historically rapid decline in fertility and mortality, as a result of which the reproduction of the population is reduced to a simple replacement of generations. This process is part of the transition from a traditional society (which is characterized by high birth rates and high death rates) to an industrial one.

The desire of organisms to survive is called uh ecological survival strategy. Ecological coping strategies are many. For example, among plants, there are three main types of survival strategies aimed at increasing the likelihood of surviving and leaving behind offspring: Violents, Patients and Explerents.

Violenti (siloviki) – suppress all competitors (for example, trees that form primary forests).

Patients– species that can survive in adverse conditions (“shade-loving”, “salt-loving”).

Explerents (filling) – species that can quickly appear where indigenous communities are disturbed - on clearings and burned areas (aspens), on shallows.

The whole variety of ecological strategies lies between two types of evolutionary selection, which are denoted by the constants of the logical equation: r- strategy and TO- strategy.

Type r- strategy, or r-selection, is determined by selection aimed primarily at increasing the rate of population growth, and, consequently, such qualities as high fecundity, early maturity, short life cycle, able to quickly spread to new habitats and survive unfavorable times in the resting stage.

Obviously, every organism experiences a combination r- And TO- selection, but r-selection dominates early stage population development, and K-selection is already characteristic of stabilized systems. But still, the individuals left by selection should have a sufficiently high fecundity and a sufficiently developed ability to survive in the presence of competition and the “press” of predators. The competition of r- and K-selection makes it possible to single out different types of strategies and rank species according to the values ​​of r and K in any group of organisms.

Population density regulation

The logical model of population growth assumes the presence of some equilibrium (asymptotic) abundance and density. In this case, the birth rate and death rate should be equal, i.e. If b=d, then there must be factors that change either the birth rate or the death rate.

The factors that regulate population density are divided into dependent and independent from density:

Dependent change with the change in density, and the independent ones remain constant when it changes. In practice, the former are biotic factors and the latter are abiotic factors.

Influence independent on the density of factors can be clearly seen in the seasonal fluctuations in the abundance of planktonic algae.

Mortality in a population may also depend directly on density. Such a phenomenon occurs in plant seeds when density dependent (i.e. regulatory) mortality occurs during the juvenile stage. Density-dependent mortality can also regulate the abundance of highly developed organisms (quite often, bird chicks die if there are too many of them and there are not enough resources).

In addition to the regulation described above, there is also self-regulation , at which the change in the quality of individuals affects the population size. Distinguish self-regulation phenotypic and genotypic.

Phenotypes - the totality of all signs and properties of an organism formed in the process of ontogenesis on the basis of a given genotype. The fact is that at high density, different phenotypes are formed due to the fact that physiological changes occur in organisms as a result of the so-called stress reactions (distress) caused by an unnaturally large concentration of individuals.

Genotypic the reasons for the self-regulation of population density are associated with the presence in it of at least two different genotypes that have arisen as a result of recombination genes.

In this case, individuals arise that are able to reproduce with more different ages and more often, and individuals with late maturity and significantly lower fecundity. The first genotype is less resistant to stress at high density and dominates during the period of peak abundance, while the second genotype is more resistant to high boredom and dominates during the period of depression.

Cyclic fluctuations can also be explained by self-regulation. Climatic rhythms and associated changes in food resources force the population to develop some kind of internal regulation mechanisms.

Mechanisms of self-regulation

Self-regulation is provided by mechanisms of inhibition of population growth. There are three hypothetical mechanisms:

1. with an increase in density and an increased frequency of contacts between individuals, stressful condition, which reduces the birth rate and increases the death rate;

2. with an increase in density, migration to new habitats, marginal zones, where conditions are less favorable and mortality increases, increases;

3. With an increase in density, changes in the genetic composition of the population occur - the replacement of rapidly breeding individuals by slowly breeding individuals. This testifies to essential role populations both in the genetic and evolutionary sense, and in a purely ecological sense, as an elementary unit of the evolutionary process, and on the exceptional importance of the events taking place at this level of biological organization for understanding both the existing dangers and “the possibilities of controlling the processes that determine the very existence of species in biosphere".

Thus, a species consists of populations. Each population occupies a certain territory (part of the species range). Over many generations, over a long period of time, the population manages to accumulate those alleles that provide high adaptability of individuals to the conditions of a given area. Since due to the difference in conditions natural selection different complexes of genes (alleles) are exposed, populations of the same species are genetically heterogeneous. They differ from each other in the frequency of occurrence of certain alleles.

For this reason, in different populations of the same species, the same trait can manifest itself in different ways. For example, northern populations of mammals have thicker fur, while southern ones are more darkly colored. In areas of the range where different populations of the same species border, both individuals of contacting populations and hybrids are found. Thus, the exchange of genes between populations is carried out, and connections are realized that ensure the genetic unity of the species.

The exchange of genes between populations contributes to greater variability of organisms, which ensures a higher adaptability of the species as a whole to environmental conditions. Sometimes an isolated population due to various random causes (flood, fire, mass disease) and insufficient numbers can completely die.

Each population evolves independently of other populations of the same species, has its own evolutionary destiny.

A population is the smallest subdivision of a species that changes over time. That is why the population is the elementary unit of evolution.

The initial stage of evolutionary transformations of a population - from the occurrence of hereditary changes to the formation of adaptations and the emergence of new species - is called microevolution.