Environmental coping strategies. Reproduction and life cycles of aquatic organisms K strategy and r strategy examples

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

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

We said that a population is a potentially immortal entity made up of mortals. To support the existence of a population, an individual must survive on its own and leave offspring who can also survive. Note the duality of this task. Probably, the greatest chances that individual will have for survival, which will not spend resources and the energy obtained from them on the production of offspring at all. But a little time will pass - and such an individual will disappear from the population without a trace. At the opposite "pole" there 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 descendants inherit an equally inefficient way of allocating resources, will produce descendants that will have no chance of survival.

This means that the greatest value for the population should have an individual that combines the costs of its own survival and the production of offspring in an optimal combination. It is possible to evaluate how this combination is optimal. To do this, it is necessary to calculate at what combination under these conditions the individual will leave the greatest possible contribution to the future generation. The measure 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 needed to achieve high reproductive value. He reproduces almost immediately after birth, gives numerous, large, protected offspring, which he takes care of; it multiplies many times and often over a long life; it wins the competition, avoids predators, and easily obtains food. It is easy to describe such a creature, but difficult to imagine.... "(Bigon et al., 1989).

You understand that this impossibility arises 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 about the alternative of maintaining the organism of its own existence and its continuation in descendants. In modern language, we can say that these parameters are connected by negative correlations, a relationship in which the improvement of the system in one parameter should be accompanied by its deterioration in another.

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

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

Features related to different adaptive strategies can be related by the relationship tradeoff, that is, insurmountable negative correlations (either-or ratio). Thus, the number of offspring and their survival rate, growth rate and resistance to stress, etc., are related to the tradeoff relationship. American ecologists R. McArthur and E. Wilson described in 1967 two types of species strategies, which are the result of two different types of selection and are linked by the tradeoff relationship. The accepted designations for 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 small, population growth is mainly influenced by the factor rN and population growth is accelerating. At this phase ( r-phase) the growth of the population is accelerating, and its number is the higher, the higher the ability of individuals to reproduce. When N becomes high enough, the cofactor begins to exert the main influence on the population size (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... The more competitive the individuals are, the higher it is.

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

It can be assumed that populations of some species are in the r-phase most of the time. In such species, individuals capable of rapidly multiplying and capturing 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 - g-strategists.

In species, whose populations are in the K-phase most of the time, the situation is completely different. The maximum reproductive value in these populations will be inherent in individuals that will be so competitive that they will be able to get their share of the resource even in conditions of its scarcity; only then will they be able to multiply 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 costs of developing each individual and increasing its competitiveness.

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

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

The dynamics of changes in the amount of available resource and the severity of competition for it are important for determining which selection (r- or K-) will act on a species. With a sharp indiscriminate reduction in the population size caused by a resource shortage caused by external reasons, r-strategists gain an advantage, and in a competitive struggle for a missing resource, K-strategists.

The choice between the r-strategy (increasing fertility) and the 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 single reproduction, while K-strategists - multiple reproduction. This feature is easier to explain with an example. Imagine mice inhabiting a barn with grain (there is plenty of resources, 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 reproduce 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 from exhaustion.

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

On the other hand, it is easy to see why typical K-strategists multiply over and over again. In a competitive environment, only the 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 bring forth one offspring at a time (like, for example, elephants and whales, and also, in most cases, humans). But no matter how perfect these animals are, a pair of parents will eventually die. In order for the population not to be suppressed, a pair of parents must leave a couple of surviving offspring, and, therefore, must give birth to more than two. If so, the necessary condition for the survival of K-strategists is the multiple reproduction of their constituent individuals.

In 1935, the Soviet botanist L.G. Ramenskiy identified three groups of plants, which he called coenotypes (the concept of strategies had not yet been formed): violets, patents, and explents. In 1979, these same groups (under different names) were rediscovered by the English ecologist J. Grime (Fig. 4.15.3). These strategies are as follows.

Rice. 4.15.3. "Grime's triangle" - classification of species strategies

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

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

- R type(from lat. ruderis, ruderal), explorer 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 (for example, dandelion, willow-herb). This allows such plants to wait for the moment of resource release or to seize free areas in time.

Many species are able to combine different types strategies. Pine belongs to the CS category as it grows well in poor sandy soils. Nettle is a CR strategist as it dominates disturbed habitats.

A species strategy can be flexible. Stratus oak - violet in the zone broadleaf forests and a patent in southern steppe... The Japanese technology of bonsai (growing bonsai in pots) can be presented as a way of converting violets into patents.

An interesting problem is the comparison of strategies according to MacArthur – Wilson and Ramensky – Grime. It is clear that r-strategists correspond to R-type organisms, explents. But K-strategists correspond not only to C-type organisms, violets, but also to those who belong to the S-type, patients. Violents maximize their competitiveness (and environmental capacity) in the face of intense competition for favorable resources for consumption, and patents - in conditions of difficult resource consumption. In other words, in the tasks that the oak, competing for light in a dense forest, and the fern, surviving in dim light in the depths of the cave, solve, there is a lot in common: the need to optimize the consumption of the resource, to improve the individual fitness of the individual.

The desire of organisms to survive is called NS a logical survival strategy. There are many ecological strategies for survival. For example, among plants, there are three main types of survival strategies aimed at increasing the likelihood of surviving and leaving behind offspring: violets, patents and experents.

Violents (enforcers) – suppress all competitors (for example, trees forming indigenous forests).

Patents– species that can survive in adverse conditions ("shade-loving", "salt-loving").

Exponents (filling) – species that can quickly appear where indigenous communities are disturbed - in clearings and burned-out areas (aspen), in shallows.

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

Type of r- strategy, or r-selection, is determined by selection aimed primarily at increasing the growth rate of the population, and, consequently, such qualities as high fertility, early maturity, short life cycle, capable of quickly spreading to new habitats and surviving an unfavorable time in the dormant stage.

It is obvious that every organism experiences a combination of r- and TO- selection, but r-selection prevails on early stage population development, and K-selection is already characteristic of stabilized systems. But nevertheless, the individuals left by selection should have a sufficiently high fertility and a sufficiently developed ability to survive in the presence of competition and the "pressure" of predators. The competition between r- and K-selection makes it possible to distinguish different types of strategies and to rank species according to the values ​​of r and K in any group of organisms.

Regulation of population density

The logical model of population growth assumes the presence of a certain equilibrium (asymptotic) number and density. In this case, fertility and mortality should be equal, i.e. if b = d, then there must be factors that change either fertility or mortality.

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

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

Influence independent on the density of factors is well traced in the seasonal fluctuations in the abundance of plankton algae.

Mortality in the population may also depend directly on the density. This occurs in plant seeds when density-dependent (ie, regulatory) mortality occurs during the adolescent stage. Density-dependent mortality can also regulate the abundance of highly developed organisms (chicks of birds often die if there are too many of them, but resources are not enough).

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

Phenotypes - a set of all the characteristics 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 gathering of individuals.

Genotypic the reasons for self-regulation of population density are associated with the presence of at least two different genotypes in it, resulting from recombinations genes.

In this case, individuals arise that can reproduce with more of different ages and more often, and individuals with late maturity and significantly lower fertility. The first genotype is less resistant to stress at high density and dominates during the period of peak population growth, and the second is more resistant to high dullness and dominates during depression.

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

Self-regulation mechanisms

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

1.with an increase in density and an increased frequency of contacts between individuals, a stressful state arises, which reduces the birth rate and increases the mortality rate;

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

3. With an increase in density, changes in the genetic composition of the population occur - the replacement of rapidly breeding by slowly breeding individuals. This indicates the most important role of the population both in the genetic and evolutionary sense, and in the purely ecological sense, as an elementary unit of the evolutionary process, and the exceptional importance of events occurring at this level of biological organization for understanding how existing dangers and "the ability to control the processes that determine the very existence of species in the biosphere."

Thus, the species consists of populations. Each population occupies a certain territory (part of the species range). For many generations, over a long time, the population has time to accumulate those alleles that ensure the high adaptability of individuals to the conditions of a given area. Since, due to the difference in conditions, various complexes of genes (alleles) are subjected to natural selection, populations of one 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 populations are more often dark-colored. In the areas of the range, where different populations of the same species border, there are both individuals of contacting populations and hybrids. Thus, the exchange of genes between populations is carried out, and links 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 habitat conditions. Sometimes an isolated population, due to various random reasons (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.

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

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

Survival- the absolute number of individuals (or percentage of the initial number of individuals) preserved in the population for a certain period of time:

Z = n / N * 100%, where Z is the survival rate,%; n is the number of survivors; N is the initial size of the population.

Survival depends on a number of reasons: the age and sex composition of the population, the action of certain environmental factors, etc.

Survival can be expressed as survival curves, which reflect how the number of individuals of the same age in the population decreases with aging.

There are three main types of survival curves:

1. type I curve characteristic of organisms whose mortality rate is low throughout life, but sharply increases at its end (for example, insects that die after laying eggs, people in developed countries, some large mammals);
2. type II curve typical for species in which mortality remains approximately constant throughout their life (for example, birds, reptiles);
3. type III curve reflects mass death individuals in the initial period of life (for example, many fish, invertebrates, plants and other organisms that do not care about offspring and survive due to a huge number of eggs, larvae, seeds, etc.).

There are curves that combine the features of the main types (for example, in people living in backward countries and some large mammals, the curve of type I at first has a sharp drop due to high mortality immediately after birth).

The complex of properties of a population aimed at increasing the probability of survival and leaving offspring is called ecological survival strategy... There are two types of ecological strategies: r-strategy and K-strategy. Characteristics are given below.

r-strategists (r-species, r-populations)- populations of rapidly breeding, but less competitive individuals. They have a J-shaped population growth curve that does not depend on population density. Such populations spread quickly, but they are unstable. These include bacteria, aphids, annual plants, etc.

K-strategists (K-species, K-populations)- populations of slowly breeding, but more competitive individuals. They have an S-shaped population growth curve, depending on the population density. Such populations inhabit stable habitats. These include man, condor, trees, etc.

And they set out in 1967 in the work "Theory of island biogeography" (eng. The Theory of Island Biogeography). It gained the greatest popularity among supporters of the heuristic approach. In the 1990s, it was criticized by several empirical studies, after which the number of its supporters began to decline.

General idea

According to the theory, natural selection in the process of evolution occurs according to one of two possible scenarios or strategies. These strategies, named r and K, are mathematically interconnected by the Verhulst equation of population dynamics:

where N is the number (or density) of the population, dN / dt is the current rate of its growth, r is the limiting rate of its growth (reproduction rate), and K is the transferred volume (the limiting number or density of the population at which the population can still exist in equilibrium with biota).

If the environment is more or less constant, then organisms with the K-strategy prevail in it, since in this case the ability to successfully compete with other organisms in conditions of limited resources comes out on top. The population of K-strategists, as a rule, is constant and close to the maximum possible under the given conditions. Characteristic features K-strategies are big sizes, a relatively long period of life and small offspring, the upbringing of which takes a significant part of the time. Typical K-strategists are large animals - elephants, hippos, whales, as well as apes and humans.

A comparative analysis of both strategies is presented in the following table:

r⁠ – ⁠K as a continuous spectrum

Despite the fact that some organisms are exclusively r- or K-strategists, most still have intermediate characteristics between these two extreme opposites. For example, trees have such inherent K-strategy traits as longevity and greater competitiveness. However, they generate a large number of diasporas and are widely distributed, which is inherent in r-strategists.

Ecological succession

In regions where major environmental disasters occur, such as, for example, it happened after a volcanic eruption on the island. Krakatoa in Indonesia or Mount St. Helens in Washington State, USA, r- and K-strategies play a very important role in ecological succession (or consistency) that restores the balance of an ecosystem. As a rule, the r-strategy plays the main role here due to its high reproductive capacity and ecological opportunism. As a result of this strategy, flora and fauna rapidly increase their potential, and as balance is restored with environment(in ecology - the climax community), the followers of the K-strategy are gradually coming to the fore.

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

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

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

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

Properties K- andR- strategies in animals.

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 use it by T.A. Rabotnov (1975), who named the so distinguished L.G. Ramensky (1936) “coenobiotic types”.

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

MacLeod was the first to draw attention to the presence of prerequisites in plants that determine their status in the community, back in 1894, who 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 complex and wrote that "capitalists" tend to have a stock nutrients, polycarpity, shading intolerance, etc.

This question received a brilliant development in the works of Ramensky, published in the 30s, where he wrote about 3 types of plants, which he called violets, patents and expellents and likened them to lions, camels and jackals.

40 years later in England, a monograph by J. Grime "Plant strategies and processes in vegetation." , in which the author, without knowing Ramensky's work, re-described the same three types of strategies called competitors, stress tolerants, and ruderals.

To understand the type of strategies, a lot was also done by E. Pianca, R. Whittaker and T.A. Rabotnov. (11)

The main systems of ecological-cenotic strategies .

E. Pianchi's system.

The Pianchi system, which is 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 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, the main item of energy expenditure is reproduction.

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

The two types of Pianchi strategy are most widespread in the plant world. And even the appearance of heterospores in lymphoids or ferns can ultimately be considered as a replacement for the r-strategy of isospores by the K-strategy of the female gametophyte, which guarantees a better survival of the offspring and replaces a huge number of small isospores with a limited number of megaspores, which provide the necessary conditions for the development of the 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 are usually polycarpics with slow development and life forms ranging from grasses to trees. In the successional series, these species increase their participation as the successional stage approaches the climax.

r-strategists, on the contrary, prefer unstable habitats characterized by disequilibrium populations, the mortality of which does not depend or depends to a small extent on density. The competition between such plants is weak, these are monocarpic juveniles, as a rule, grasses, less often shrubs. In the succession series, they are associated with pioneer stages and do not play a significant role in mature communities preceding menopause.

Thus, E. Pianchi's type system is simple - one-dimensional, but it fully corresponds to the continual 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 the extreme options, as a rule, are connected by a whole range of transitions (E. Pianca, 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. Its system is based on the patterns of population fluctuations between two limits: K-upper limit corresponding to the maximum saturation density and L-lower limit, meaning a certain "population zero" corresponding to the number that is not able to ensure the survival of the population.

K-strategists strive to achieve the K level, achieving this, first, through the ultimate differentiation of niches. K-selection affects the mechanisms by which they preserve their population in the process of competition and other interactions within the boundaries of the environment they occupy. The number of populations is significantly decreasing, however, the general tendency of such populations is fluctuations around the level of K.

The second group of populations is the r-strategist. 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 diaspora production; they are poorly adapted both to conditions of heightened competition and to unfavorable conditions causing stress.

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

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

If we compare the systems of Whittaker and Pianchi, it is obvious that his types K and r correspond to K and r of Pianchi, and indeed the differentiation of niches is under the influence of K-selection. These are mainly perennial species that often reproduce vegetatively and consume relatively little energy in the generative sphere.

Ruderal plants, on the other hand, are distinguished by a shortened life cycle and high seed productivity, and therefore the costs of reproduction are 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 productivity (the result of r-selection), but dwarf shrubs, as well as some herbaceous sod plants undergo stress in the vegetative state and therefore represent the result of the action of K -selection. (10)

Ramensky-Greim system.

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

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

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

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

In the future, the views and classification of L.G. Ramensky (1935-38) were developed by Rabotnov T.A. (1966, 1975, 1978, 1980). He showed the complex nature of patient (stress tolerance) in plants and isolated 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 the patents of 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 by minimizing the processes of vital activity. Their synecological and autecological optima usually do not coincide. (6 )

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

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