The action of the elementary factors in the gene pool changes the frequency of certain genes, which leads to changes in the genotype and phenotype in a population, and prolonged exposure to natural selection takes its differentiation.
What microevolution
Microevolution - population changes under the influence of evolutionary factors that may lead to a change in the gene pool, or even the appearance of a new species.
factors of evolution can be called any process or phenomenon.Among them should be called mutations, isolation, genetic drift, population waves that alter the genetic make-up.
size of any population is constantly changing.The reasons for this are the various effects of biotic and abiotic nature.Such fluctuations in population numbers are periodic.So, after the increase in the number of individuals in a population is its reduction.In 1905 Chetverikov called this pattern of population waves.If examples of population waves, it may be fluctuations in the number of victims of predators, breeding locusts or rabbits in Australia.An example can also serve as outbreaks of lemmings in the Arctic or the plague epidemic, which in the past were recorded in Europe.
Feature "waves of life»
These waves are characteristic of all living organisms.They may be periodic or aperiodic.Periodic often observed in short-organisms - in insects, annual plants, as well as the majority of microorganisms and fungi.The simplest example may be seasonal changes in abundance.
Non-recurrent waves of population depend on a combination of several complex factors.Generally, they relate to not one but several types of organisms in biogeocoenose so can lead to a radical restructuring.
Among the changes in the number of individuals in the population should be made a sudden appearance of certain organisms to new areas where there are no natural enemies.Also worth mentioning is the sharp change in the number of non-cyclic, which are associated with the natural "catastrophes" and can manifest biogeocoenose or destruction of a landscape.For example, several dry summers can make a significant territory - led to the emergence of meadow vegetation in the marshes and a large number of dry meadows.If
population waves, the reason it is necessary to remember not only the relationship of living organisms with each other and with environmental factors, but also to human influence.
evolutionary significance of "waves of life»
In cases where the number of any population is sharply reduced, may be only a few individuals.At the same time they have the frequency of genes (alleles) is different from the one that was in the original population.If, after a sharp decline in the number of population is its sharp rise, the beginning of a new outbreak of the growth of the number of individuals in the population gives a small group of organisms that remain.That is why it can be argued that the population waves affect the gene pool because the genotype of the group determines the genetic structure of the whole population.
This completely random set of mutations dramatically change in the population and their concentration.Thus, some of the mutations disappears completely and some suddenly grow.To sum up, we can say that the population waves as an evolutionary factor is extremely important because the subject of intense selection is a major supplier of evolutionary material as rare mutations are substituted by the selection.
addition, the waves of life are able to temporarily withdraw a number of genotypes or mutations in other abiotic or biotic environment.Despite this, even the combination of population waves and the mutation does not provide flow of the evolutionary process.It is necessary to effect the factors that affect in one direction (this is, for example, insulation).
Insulation effect on population size
This factor is extremely important in evolutionary terms, since provokes the emergence of new features in terms of one species does not occur, and the crossing of different species to each other.It is worth noting that most observed geographical isolation.Its essence lies in the fact that the only area of breaks, and the intersection of individuals from different parts becomes impossible or difficult.
is worth noting that in the isolated population accidentally develop a mutation and natural selection of its genotype is becoming more diverse.In addition, there are environmental isolation and a variety of biological mechanisms that prevent individuals of different species interbreed.An example may have different preferences regarding the place or time of crossing, as well as, for example, different behavior or different structure of the genital organs of animals, which becomes an additional barrier to interbreeding.
If we generalize, we can say that different types of insulation contribute to the formation of new species, but at the same time help to preserve the genetic structure of the species.
Gene flow
random change in the number of genes in any population of small size may have a significant impact because it could lead to a change in allele frequencies.Random change in allele frequency is called genetic drift.This process is non-directional in nature.It was first discovered by geneticist NP Dubinin and DD Romashov.
confirmation regarding the random genetic drift was C. Wright.He crossed the laboratory male and female fruit flies that were heterozygous for a particular gene.Thereafter progeny was obtained with a concentration of normal and mutant gene, which was 50%.After several generations, some individuals become homozygous for the mutant gene, some even lost it, and another part of the individuals had both mutant and normal gene.
It should be noted that even with the reduced viability of mutant animals, and provided the influence of natural selection of mutant allele could completely replace the normal, causing specific population waves.
Etiology population waves
Of all the causes that may affect the quantitative characteristics of the population, leading place climate, biotic factors in this case are assigned to the background.At low species diversity number of individuals in the population depends on the weather, the chemical composition of the environment, as well as on the degree of contamination.
It should be noted that the causes of population waves that determine changes in population, depend on its density, or influence, regardless of this setting.
abiotic and anthropogenic factors, as a rule, do not depend on the density of population.Biotic impact is increasingly dependent on it.Note territorial behavior, which in the course of evolution is the most effective mechanism that restrains the growth of the number of individuals in the population.Thus, the activity of individuals is limited by the appropriate space.By increasing the number of developing intraspecific competition for resources or direct antagonism (the attack on the competitors).
population waves also depend on behavioral responses to high population characterized by the appearance of a mass migration instinct.It may also develop a stress reaction in which individuals have developed such physiological features that reduce fertility and contribute to increased mortality.So, the process is disturbed oogenesis and spermatogenesis, more and more cases of miscarriages, decreases the number of individuals in one generation and increases during puberty.In addition, reduced brood care instinct, behavior changes - increasing aggressiveness, cannibalism can be observed and inadequate response to the opposite sex, which ultimately reduces the size of the population.
Features of change in populations
Many environmental processes associated with the proliferation of the population of its range or the number of local outbreaks, resemble a kind of waves that, as mentioned above, were called "waves of life".A typical example is the sudden increase in the number of insects in a limited area of the forest.Under favorable conditions, the insects are capable of capturing more and more territory, which is the typical pattern of increasing their density or distribution of the so-called population wave.Knowing the characteristics of mobility and certain population characteristics, you can easily calculate the velocity of propagation of this wave and possible control methods.
Similarly, we can characterize the epidemic wave, so this theory successfully used to determine the nature of the spread of various diseases and the speed of the process.
In addition, mention should be made of population genetic waves with which describe the propagation of a particular gene of its range, which occupies one or the other population.
mechanism of action of population waves
population waves can be described by a model example.Thus, in the closed box is black and 500 is the same amount of white balls, which corresponds to the R-allele frequency of 0.50.If you delete a random 10 balls and assume that 4 of them have a black color, and 6 - white, then, respectively, allele frequency will be 0.40 and 0.60.
If you increase the number of balls in 100 times with 400 black and 600 white, and then again at random pick all 10, then it is likely that the ratio of the color will be significantly different from the original, for example, 2 black and white 8.The frequency of alleles, respectively, will be P-0.20 and P-0.80.If we take a third sample, there is a possibility that will be extracted 9 out of 10 white balls selected, or all of them will have a white color.
of this example can be seen on the random fluctuations of allele frequencies in natural populations, which may reduce or increase the concentration of a particular gene.
