27.Ecological strategies of populations (r- and k-life strategies). Their ecological meaning.
Adaptations of individuals in a population are ultimately aimed at increasing the likelihood of survival and leaving offspring. Among the adaptations, a complex called ecological strategy stands out. The ecological strategy of a population is its general characteristics of growth and reproduction. This includes the growth rate of its individuals, time to reach sexual maturity, fertility, frequency of reproduction, etc.
There are two survival strategies - the p strategy and the k survival strategy.
Ecological strategies of populations are highly diverse. Thus, when presenting the material on population growth and growth curves, the symbols r and K were used. Rapidly reproducing species have a high r value and are called r-species. These are, as a rule, pioneer (often called “opportunistic”) species of disturbed habitats. These habitats are called r-selective because they favor the growth of r-species.
Species with relatively low r values are called K-species. Their reproduction rate is sensitive to population density and remains close to the equilibrium level determined by the value of K. These two types of species are said to use the r-strategy and the K-strategy, respectively.
These two strategies essentially represent two different solutions to the same problem - the long-term survival of the species. Species with a g-strategy quickly colonize disturbed habitats (exposed rock, forest clearings, burnt areas, etc.) than species with a K-strategy, because they spread more easily and reproduce faster. Species with a K-strategy are more competitive, and they usually displace r-species, which in the meantime move to other disturbed habitats. The high reproductive potential of r-species indicates that, if left in any habitat, they would quickly use up the available resources and exceed the supporting capacity of the environment, and then the population would die. Species with an r-strategy occupy a given habitat for one or at most several generations. Later they move to a new place. Individual populations may die out regularly, but the species moves and survives. In general, this strategy can be described as a “fight and flight” strategy.
It should be noted that different populations can use the same habitat in different ways, so species with r- and K-strategies can coexist in the same habitat. There are transitions between these extreme strategies. No species is subject to only r- or only K-selection. In general, r- and K-strategies explain the relationship between different qualitative characteristics of the population and environmental conditions.
28. Survival and survival curves of organisms in a population, the ecological meaning of survival curves.
Lifespan is the duration of an individual's existence. It depends on genotypic and phenotypic factors. There are physiological, maximum and average life expectancy. Physiological life expectancy (PLS) is the life expectancy that an individual of a given species could have had if it had not been influenced by limiting factors throughout its entire life. It depends only on the physiological (genetic) capabilities of the organism and is only possible theoretically. Maximum life span (MLS) is the life span to which only a small proportion of individuals can survive under real environmental conditions. It varies widely: from a few minutes in bacteria to several thousand years in woody plants (sequoia). Typically, the larger the plant or animal, the longer its lifespan, although there are exceptions (bats live up to 30 years, which is longer, for example, than the life of a bear). Average life expectancy (ALS) is the arithmetic average of the life expectancy of all individuals in a population. It fluctuates significantly depending on external conditions, therefore, to compare the life expectancy of different species, genetically determined LRM is more often used.
Survival rate is the absolute number of individuals (or percentage of the original number of individuals) surviving in a population over a certain period of time.
Z = n/n 100%,
where Z is survival rate, %; n – number of survivors; N – initial population size.
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 in the form of tables and survival curves. Survival tables (demographic tables) and survival curves show how the number of individuals of the same age in a population decreases as people age. Survival curves are constructed using data from survival tables.
There are three main types of survival curves. Type I curve is characteristic of organisms whose mortality rate is low throughout life, but increases sharply at the end of its life (for example, insects that die after laying eggs, people in developed countries, some large mammals). Type II curve is typical for species in which mortality remains approximately constant throughout life (for example, birds, reptiles). Type III curve reflects the mass death of individuals in the initial period of life (for example, many fish, invertebrates, plants and other organisms that do not care about their 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, curve I initially has a sharp drop due to high mortality immediately after birth).
The set of properties of a population aimed at increasing the probability of survival and leaving offspring is called an ecological survival strategy. This is a general characteristic of growth and reproduction. This includes the growth rate of individuals, time to reach maturity, fertility, frequency of reproduction, etc.
Thus, A.G. Ramensky (1938) distinguished the main types of survival strategies among plants: violents, patients and explerents. Violents (siloviki) - suppress all competitors, for example, trees forming indigenous forests. Patients are species that can survive in unfavorable conditions (“shade-loving”, “salt-loving”, etc.). Explerents (fillers) are species that can quickly appear where indigenous communities are disturbed - in clearings and burnt areas, on shallows, etc.
More detailed classifications also identify other intermediate types. In particular, it is possible to distinguish another group of pioneer species that quickly occupy newly emerging territories where there has not yet been any vegetation. Pioneer species partially have the properties of explorers - low competitive ability, but, like patients, they have high tolerance to the physical conditions of the environment.
Populations of species in which fertility and mortality largely depend on the action of external factors quickly change their numbers. Periodic changes in population numbers are called population waves. In some cases, the number changes thousands and millions of times. These populations rarely reach the size K and exist due to the high value of r. This method of reproducing populations is called r-strategy.
R-strategies: (Selection for the number of descendants)
1. High fertility
2. Short regeneration time
3. High numbers
4. Usually small sizes of individuals (small seeds in plants)
5. Short life expectancy, high energy expenditure for reproduction
6. Short duration of habitats
7. Low competitiveness
r-Strategists (explerents) are characterized by low competitiveness, high fertility, lack of care for offspring, rapid development and short life expectancy. 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 fertility and mortality largely depend on their density (that is, on the characteristics of the population itself) are less dependent on the action of external factors. They maintain numbers close to the value of K, therefore the method of reproducing such populations is called the K-strategy.
K-strategy: (Selection for 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 of lifestyle
6. caring for offspring
K-Strategists (violents) are characterized by high competitiveness, low fertility, care for offspring, prolonged development and long life expectancy. K-Strategists are figuratively called “lions” because they are able to hold ecological space for a long time.
In addition to the r-strategy and K-strategy, there is also an S-strategy. S-Strategists (patients) inhabit habitats with unfavorable living conditions for most organisms, in which there is practically no competition. Therefore, S-strategists are figuratively called “camels.” By their low value of r they are close to “lions” (violents), and by their high value of K they are close to “jackals” (explerents). In terms of development time and lifespan, S-strategists can be similar to both r-strategists and K-strategists.
Large (global) human populations at a certain stage are characterized by hyperbolic growth
Opening Heinz von Foerster(Science, 1960): The growth of the Earth's population from ancient times to the 1960s and 1970s is described by a very simple equation and precise graph - hyperbole(R 2 = 0.996, for the period 1000 – 1970)
Proof that Human growth is not exponential: the specific growth rate increases with population growth (through a decrease in mortality)
The reasons for hyperbolic growth - in addition to the “usual” positive feedbacks of unlimited exponential growth of any population, act in human society its additional “accelerators”.
For any level of technological development, there is a strictly defined level of population ( Simon Kuznets - Michael Kremer hypothesis) the rate of technological growth are 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(the more people, the more potential inventors and innovators among them). This results in a system of double positive feedbacks., which spins the flywheel of hyperbolic population growth in the world: technological growth - growth of the ceiling of the Earth's carrying capacity - demographic growth - more potential inventors - acceleration of technological growth - accelerated growth of the Earth's carrying capacity - even faster demographic growth - 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 load-bearing limit of the environment, set by the next leap in the growth of technology, epidemics, wars, famines and other horrors periodically arose during the period of hyperbolic growth (the so-called “ Malthusian trap»).
But as we approached the general limit of environmental saturation (K), negative feedback connections began to arise, already inhibiting growth (female literacy, family planning) through a decrease in the birth rate. Growth rates decreased mainly due to a reduction in the birth rate (K-strategy), whereas 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. Then a period of declining growth rates began, due to the general demographic transition, when social factors first reduced the mortality rate, and a little later reduced the birth rate. 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 raise, albeit few, but high-quality descendants. For people, this means, first of all, educated people, i.e. competitive. And this costs more and more. And there is no longer a need to have many children, as in an agrarian society.
Demographic transition is a historically rapid decline in fertility and mortality, as a result of which population reproduction is reduced to simple replacement of generations. This process is part of the transition from a traditional society (characterized by high birth rates and high deaths) to an industrial one.
The desire of organisms to survive is called uh ecological survival strategy. Ecological survival strategies are many. For example, among plants there are three main types of survival strategies aimed at increasing the likelihood of surviving and leaving offspring: violents, patients and explerents.
Violents (security forces)) – suppress all competitors (for example, trees forming indigenous forests).
Patients– species that can survive in unfavorable conditions (“shade-loving”, “salt-loving”).
Explerents (fillers) – species that can quickly appear where indigenous communities are disturbed - in clearings and burnt areas (aspens), on shallows.
The entire diversity of ecological strategies lies between two types of evolutionary selection, which are indicated by the constants of the logical equation: r- strategy and TO- strategy.
Type r-strategy, or r-selection, determined by selection, aimed primarily at increasing the rate of population growth, and, consequently, such qualities as high fertility, early maturity, short life cycle, capable of quickly spreading to new habitats and surviving unfavorable times in the dormant stage.
Obviously, every organism experiences a combination r- And TO- selection, but r-selection predominates at the early stage of population development, and K-selection is already characteristic of stabilized systems. But still, the individuals retained by selection must have sufficiently high fertility 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 distinguish different types of strategies and 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, the birth rate and death rate should be equal, i.e. If b=d, then factors must operate that change either fertility or mortality.
Factors regulating population density are divided into dependent and independent from density:
Dependents change with a change in density, and the independent ones remain constant as it changes. In practice, the first are biotic, and the second 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. This phenomenon occurs in plant seeds when density-dependent (i.e., regulatory) mortality occurs during the adolescent stage. Density-dependent mortality can also regulate the numbers of highly developed organisms (bird chicks quite often 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 , in which the population size is affected by a change in the quality of individuals. Self-regulation is distinguished phenotypic and genotypic.
Phenotypes – the totality of all the characteristics and properties of an organism formed in the process of ontogenesis based on a given genotype. The fact is that at high densities, 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 crowd of individuals.
Genotypic the reasons for self-regulation of population density are associated with the presence in it of at least two different genotypes that arose as a result recombination genes.
In this case, individuals arise that are capable of reproducing at more different ages and more frequently, 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, while the second is more resistant to high boredom and dominates during the depression period.
Cyclical 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.
Mechanisms of self-regulation
Self-regulation is ensured 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 increasing density, migration to new habitats, marginal zones, where conditions are less favorable and mortality increases, increases;
3. As density increases, changes in the genetic composition of the population occur - replacement of rapidly reproducing individuals with slowly reproducing ones. This indicates the most important role of the population, both in a genetic-evolutionary sense and in a purely ecological sense, as an elementary unit of the evolutionary process, and about the exceptional importance of events occurring at this level of biological organization for understanding both existing dangers and “opportunities for managing processes, determining the very existence of species in the 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 ensure the high adaptability of individuals to the conditions of a given area. Since different sets of genes (alleles) are subject to natural selection due to different conditions, 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 differently. For example, northern populations of mammals have thicker fur, while southern ones are more often dark-colored. In areas of the range where different populations of the same species border, both individuals of contacting populations and hybrids are found. Thus, genes are exchanged between populations, 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 reasons (flood, fire, mass disease) and insufficient numbers, can completely die.
Each population evolves independently of other populations of the same species and has its own evolutionary fate.
A population is the smallest subdivision of a species that changes over time. This is why a 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.
The most clearly opposing strategies of social contacts manifest themselves, of course, in reproductive behavior, i.e. in breeding strategy.
In most species, including humans, both reproductive strategies are found. The general direction of human evolution can be designated as a movement from r-strategies to K- strategies. You can even indicate the approximate time when K- the strategy began to prevail - this is the 3rd millennium BC, when the myth of the conflict between Niobe and Latona arose in the territory of Asia Minor.
Niobe refused to make sacrifices to Latona and her children from Zeus to Apollo and Artemis. She explained this, in part, 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 a few descendants, but more adapted to the environment, which in competition will defeat more numerous, but worse adapted individuals. And the greater adaptive capabilities of the offspring are achieved, as already noted, firstly, by careful selection of a reproductive partner and, secondly, by careful care of the offspring - what in humans is called upbringing and training.
In human evolution r-strategy is gradually being replaced TO-strategy.
Evolutionary advantage passed to K- strategists, i.e. those women who: 1) carefully chose their reproductive partner (spouse) and 2) had pronounced parental behavior, i.e. provided children with careful care, raised them and gave them education.
Woman K-the strategist is interested in the reproductive partner spending all the resources obtained to provide only for her offspring.
Despite the fact that in general humans are a monogamous species (more precisely, among humans there are more representatives K-strategies), there are often carriers of the opposite reproductive strategy, who are quite indifferent to their children. Such people, especially women, often feel painfully about their indifference, considering themselves to blame for the lack of parental feelings. Doctors classify this condition as a special “bad mother” neurosis.
The type of reproductive strategy to which a person belongs is revealed only after the birth of his child. Then the hormonal reaction accompanying childbirth initiates a complex of parental behavior. It is difficult to determine whether a woman belongs to one or another psychological type before giving birth. -r- or TO- strategies. You cannot raise attention to your own children.
Coldness or hostility of a woman towards her children are variants of the norm. This is an extreme manifestation r-reproduction strategies.
If a healthy woman has high levels of cortisol at rest, i.e. If she belongs to psychological type B, this serves as a 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, parental affiliation bias is reflected in the estradiol to progesterone ratio. 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. Very little is known about the parental behavior of men. There is evidence that parenting 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 significance of the study of biological markers K-strategies are obvious. A woman makes different, largely contradictory, demands on her sexual and reproductive partner. If a lover should have the maximum number of advantages, then the husband should have a minimum number of disadvantages. And only two positive qualities: bringing money and treating children well. Therefore, the problem of choosing a spouse will be greatly facilitated when specific biological signs of a person’s inclination to behavior that ensure K- breeding strategy. Unfortunately, this problem is still far from being resolved.
It should be noted that the behavior characteristic of the two reproduction strategies is manifested not only in relationships with children and spouses. Reproductive behavior strategies are a special case of social contact strategies.
Choose - me or this cat!
Well, I choose you. After all, I’ve known you for a long time, but this is the first time I’ve seen this cat.
E. Uspensky
The character of E. Uspensky is obvious K- strategist, because if an alternative choice is necessary, he prefers a person he knows well. The owner of the opposite psychological type will choose a stranger, since communication with him promises new impressions and is more interesting.
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 reactions to the behavior of another animal. Type A rats are indifferent to the behavior of their neighbor. The differences in the oxytocin system of these animals are very revealing. In type A animals, the activity of the oxytocin system is two times lower than in type B animals. Thus, there is a correspondence to the differences in humoral mechanisms and types of social contacts in animals of genetically selected lines.
Let's look at a few examples of the effect of oxytocin on human behavior.
Volunteers were given intranasal oxytocin, which increased trust between people.
Moreover, early social stress caused by maternal separation leads to altered oxytocin levels in adults. For example, in rhesus monkeys that were raised in isolation from their mother, at the ages of 18, 24 and 36 months, the number of affiliative social contacts, including the duration of allogrooming, was dramatically reduced, and the number of agonistic contacts and the duration of stereotypic motor acts was increased. In such isolates, the concentration of oxytocin in the cerebrospinal fluid is significantly lower than in normal isolates, i.e. monkeys raised with their mother.
Similar results were obtained in a study of people with a lack of contact with parents. Children who have been deprived of maternal care from birth become adults who suffer from emotional disturbances and exhibit impaired social behavior. They also show reduced activity of the oxytocin and vasopressin systems 147 . Disturbances in the oxytocin system have also been noted in children deprived of their father’s presence. Children of single mothers are known to 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-induced rise in cortisol in the blood is weakened
Summarizing 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 relationships 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 behavioral styles are genetically determined but can be altered, at least temporarily, by manipulating the body's oxytocin levels.
Ecological strategies of populations
Whatever the adaptations of individuals to living together in a population, whatever the adaptations of the population to certain factors, they are ultimately aimed at long-term survival and continuation of themselves in any conditions of existence. Among all the adaptations and features, one can distinguish a set of basic characteristics, which are called an ecological strategy. This is a general characteristic of the growth and reproduction of a given species, including the growth rate of individuals, the period when they reach sexual maturity, the frequency of reproduction, the maximum age, 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 reproducing species (r-species); it is characterized by selection for increased population growth rates during periods of low density. It is typical for populations in environments with sudden and unpredictable changes in conditions or in ephemeral, ᴛ.ᴇ. existing for a short time (drying puddles, water meadows, temporary watercourses)
The main characteristics of r-species: high fertility, short regeneration time, high numbers, usually small sizes of individuals (plants have small seeds), short life expectancy, large expenditures of energy on 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 - they are replaced by K-species.
r-species include bacteria, all annual plants (weeds) and insect pests (aphids, leaf beetles, stem pests, gregarious phase of locusts). Among perennials - pioneer species: fireweed, many grasses, wormwood, ephemeral plants, among tree species - willow, white and stone birch, aspen, choicenia, among conifers - larch; they appear first on disturbed lands: burnt areas, mountain ranges, construction quarries, along roadsides.
K-strategy – this strategy is possessed by species with a low reproduction rate and high survival rate (K-species); it determines selection for increased survival at high population densities approaching the limit.
The main characteristics 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 reproduction rate of K-species decreases as the maximum population density approaches and increases rapidly at low densities; parents take care of their offspring. K-species often become dominant in biogeocenoses.
K-species include all predators, humans, relict insects (large tropical butterflies, including Far Eastern ones, relict longhorned beetle, stag beetle, ground beetles, etc.), a single phase of locusts, almost all trees and shrubs . The most striking representatives of plants are all conifers, Mongolian oak, Manchurian walnut, hazels, maples, forbs, and sedges.
Different populations use the same habitat in different ways, and therefore species of both types can exist in it at the same time using a strategy.
EXAMPLES. In the forests on the ecological profile "Mountain Taiga" in the spring, before the leaves bloom on the trees, ephemeroids rush to bloom, bear fruit and finish the growing season: corydalis, Adonis Amur, anemone, oriental violet (yellow). Under the forest canopy, peonies, lilies, and crowberry begin to bloom. In open areas in dry oak forests on the southern slope, sheep fescue and roseate grass grow. Oak, fescue and other species are K-strategists, marianberry is r-strategist. 40 years ago, after a fire, parcels of aspen (r-species) formed in the fir-broadleaved forest type. Today, aspen is leaving the forest stand, being replaced by K-species: linden, oak, hornbeam, walnut, etc.
Any population of plants, animals and microorganisms is a perfect living system, capable of self-regulation and 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 that regulate relationships between populations of different species are also widespread in nature. The regulator of these relationships is a biogeocenosis consisting of many populations of different species. In each of these populations, interactions occur between individuals, 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. writes Schmalhausen: “...In all biological systems there is always interaction between different regulatory cycles, leading to the self-development of the system in accordance with the given conditions of existence...”
When optimal ratios are achieved, a more or less long stationary state (dynamic equilibrium) of the given system occurs under the given conditions of existence. "...For a population, this means the establishment of a certain genetic structure, including various forms of balanced polymorphism. For a species, this means the establishment and maintenance of its more or less complex structure.... For a biogeocenosis, this means the establishment and maintenance of its heterogeneous composition and established relationships between components. When the conditions of existence change, the stationary state, of course, is disrupted. There is a reassessment of the norm and options, and, consequently, a new transformation, ᴛ.ᴇ. further self-development of these systems...” At the same time, the relationships between links in the biogeocenosis change, and in populations there is a restructuring of the genetic structure.
Ecological strategies of populations - concept and types. Classification and features of the category "Ecological strategies of populations" 2017, 2018.
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