Lesson fluctuations in the number of organisms Environmental regulation. The fluctuations in the number of organisms cyclic and non-cyclic oscillations
In nature, populations are experiencing fluctuations. Thus, the number of individual populations of insects and small plants can reach hundreds of thousands and a million individuals. In contrast, the populations of animals and plants can be relatively small in terms of numbers.
The operation of regulatory mechanisms can cause population fluctuations. Three main types of population dynamics can be distinguished: stable, cycled and jump-shaped (explosive).
Any population cannot consist of a smaller number of individuals than necessary to ensure the stable implementation of this environment and the stability of the population to factors. external environment - The principle of the minimum size of the population.
Minimum population Specified for different types. The output beyond the minimum leads a population to death. So, further crossing the tiger on Far EastInevitably leads to extinction due to the fact that the remaining units, not finding with a sufficient frequency of partners for reproduction, will be cleaned throughout the few generations. This threatens and rare plants (Orchid "Venerine Shoe" and others).
There is also a population maximum. 1975, Odum, - the rule of the population maximum:
The population density regulation is carried out when energy and space resources are fully used. A further increase in the population density leads to a decrease in food security and, therefore, to a decrease in fecundity.
Discern non-periodic (rarely observed) and periodic (permanent) fluctuations in the number of natural populations.
A stable type is characterized by a small scope of oscillations (sometimes the number is increased several times). Property of species with well-pronounced mechanisms of population homeostasis, high survival, low fertility, large life expectancy, complex age structure, developed concern about the offspring. Whole complex Effectively working regulatory mechanisms keep such populations at certain limits of density.
Periodic (cyclic) population fluctuations. Trends usually for one season or several years. Cyclic changes with lift lifting on average after 4 years is registered in animals living in the tundra - lemming, polar owls, sand. Seasonal fluctuations in numbers are characteristic of both many insects, miserable rodents, birds, small aquatic organisms.
Can lead to fluctuations in population numbers?
All living on Earth changes.
Changes underlie the evolution of organisms, at the heart of the development of all ecological systems without exception.
The most important environmental processes include the dynamics of populations, i.e., changes in the number of components of their organisms.
The populations would not be able to exist in changing conditions of the external environment without changing with them. Population changes are a complex process that provides stability of populations, the most efficient use of environmental resources, finally changes in the properties of themselves organisms In accordance with the changing conditions for their lives.
Consider the mechanisms of changes in population numbers.
Each population of plants or animals can be characterized by reproduction rate, or fertility. Birth rate is expressed by the number or shares of individuals (eggs, seeds), born (hatched, pending) in population per unit time. The fertility is determined by the properties of both organisms (for example, fecalness of females) and their populations (composition, abundance, etc.).
In any natural population, the number of nascent individuals always exceeds the number of their parents. This is easy to see, remembering how much seed gives one plant or how many young produce, for example, a cat, a wolf, a squorter, a frog or fish. Due to the birth rate, the population is striving for unlimited growth.
However, not all individuals of new broods can live to mature age and leave offspring. Some of them die. The rate of dieting organisms is called mortality. Mortality is expressed by the number or shares of individuals perishing per unit of time. Mortality limits the population growth.
Both fertility and mortality constantly change depending on the set of factors. When the fertility exceeds the mortality, the population increases, and vice versa: the number decreases when mortality becomes higher than the birth rate. Constant changes in the living conditions of organisms lead to a strengthening of one, then another process. As a result, the number of populations fluctuates.
The ability to change allows populations to constantly adapt to changing living conditions. For example, the emergence of free resources leads to an increase in the birth rate, an increase in the number and expansion of the territorial boundaries of populations (as described in the weakening of competitive pressure), and vice versa. Population fluctuations can be caused by seasonal changes in living conditions - temperature, humidity, illumination.
Sometimes the reasons that cause vibrations of the number of populations can be in them themselves. This happens when the mortality rate or fertility of organisms changes in response to changes in their numbers, more precisely, the population density, i.e. the number of individuals per unit area.
The mechanisms of this kind are called regulatory, they work automatically when the population density reaches or too high, or too low values.
Regulatory mechanisms may have the nature of behavioral or physiological reactions of organisms to change the population density.
There are cases when in overpopulation conditions in a number of mammals There are sharp changes in the physiological state, which affects animal behavior, reduces their resistance to diseases and other adverse effects.
Belyaky hares, for example, during the periods of the peak of the number often suddenly die from the "shock disease". In some species of fish at high population density, adults are transferred to food with their young people, as a result of which the population is beginning to decline. Improving mortality and decline in fertility under the influence of high density are observed in populations of many species of animals and plants. In all these cases, the signal to the response of regulatory mechanisms gives the population itself, more precisely, its density.
The operation of regulatory mechanisms can cause cyclic vibrations of population numbers.
An example of cyclic changes give vibrations of the number of certain types northern mammals. For example, cycles of three- and four-year periodicity are characteristic of many northern mice rodents - mice, voles, lemming, for polar owls, Pesttsy, etc.
In the course of evolution, various types of living organisms acquire various properties. This is reflected in the properties of their populations, in the peculiarities of the number of numbers. The population of species adapted to the existence in stable, albeit and harsh conditions (penguins, whales, white bears) are usually not capable of rapid changes in numbers. Without human intervention, their number varies smoothly, without sharp peaks or failures. Such a picture of the dynamics is characteristic of organisms having a long development cycle, whose population includes many age groups. In the same reservoir, for example, the number of pussy, whose population consists of 25 age groups, changes much slower than the number of acne, the population of which includes only 6 age groups.
Other species living in zones moderate climate Especially annual animals (most insects) and plants (some types of herbs) are capable of rapid and sharp change in the number. These changes are characterized by a wide range. During the minimum and maximum abundance, the number of such species may vary in tens, hundreds, and sometimes - thousands of times. For these species, "population explosions. - sharp explosive increments of the number that occur almost suddenly. This happens when there are particularly favorable conditions for organisms reproduction. The population of this type is usually the first to populate new habitats in the communities on early stages of its development.
In mature ecosystems, including many different types of plants, animals and microorganisms, where biotic bonds are developed and the distribution of used resourcesThe relationship of the type of competition or predation becomes the main reason for fluctuating the number of individual species.
Biotic relationships act as peculiar regulators, they suppress "population explosions", translate indiscriminate changes in the form of correct periodic cake in, in some cases stabilize the number of organisms.
Here we face important properties that have ecological systems of different levels of the organization (community, populations, ecosystems):
the functioning of a separate element of the system is determined by its connections with other elements;
separate elements are interchangeable: the loss of one leads to the fact that its functions begins to perform
another element occupies a similar position in the system.
This is another type of regulation.
Communities How to regulate the changes occurring in separate populations of the population help the ecosystem to maintain its properties even with the loss of those or other items. With the disappearance of one type, its place occupies another, the first to position in the trophic structure of the community.
An example is the usual changes. species composition Fish in water bodies where fisheries develops. Reducing the number of the most valuable species due to catch often leads to an increase in the number of so-called "weed" fish, which are not interested in fishermen. The species wealth decreases, although the total number of fishes remains unchanged.
MicroEvolutionary processes are closely related to population dynamics. The probability of changes in the gene pool (violation of its equilibrium) is particularly increasing when the population is low. Consequently, during the years of low numbers, microevolutionary processes must proceed more actively. If we consider that the decrease in the number of organisms occurs with sharp changes in external factors, it can be understood that the driving selection begins to increase in the same moments. In other words, faced with changes in living conditions, the population answers them not only by changes in the number, but also by the changes in the organisms themselves: the individuals are preserved in the population only with those properties that are useful in these specific conditions.
In periods of lifting the number, the acquired changes are fixed in the population. Stabilizing selection begins. This is the adaptation, the adaptation of organisms to new living conditions.
Dynamics of populations. Fertility. Mortality. Regulatory mechanisms. Cyclic fluctuations in numbers.
1. What is the dynamics of populations? What factors cause population fluctuations?
2. What is the value of the dynamics of populations in nature?
3. What are regulatory mechanisms? Give examples.
Kamensky A. A., Kriksunov E. V., Book V. V. Biology Grade 9
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Type of lesson - combined
Methods: Partially search, pro-bleed presentation, reproductive, explained-illustrative.
Purpose:
Awareness of students' significance of all discussed issues, the ability to build their relations with nature and society based on respect for life, to the whole living as a unique and invaluable part of the biosphere;
Tasks:
Educational: show the multiplicity of factors acting on organisms in nature, the relativity of the concept of "harmful and useful factors", the diversity of life on the planet Earth and options for adaptations of living beings to the entire spectrum of habitat conditions.
Developing: develop communication skills, the ability to independently produce knowledge and stimulate their cognitive activity; The ability to analyze information, allocate the main thing in the material being studied.
Educational:
Briefing the culture of behavior in nature, the quality of the tolerant personality, instilling interest and love for wildlife, form a sustainable positive attitude towards each living organism on Earth, to form the ability to see excellent.
Personal: Cognitive interest in ecology .. Understanding of non-accuracy of obtaining knowledge about the variety of biotic connections in natural co-societies to save natural biocenoses. The ability to choose targeted and semantic installations in their actions and actions in relation to wildlife. The need for a fair assessment of their work and work of classmates
Cognitive: skill to work with various sources of information, pre-form it from one form to another, compare and analyze information, draw conclusions, prepare messages and presentations.
Regulatory: The ability to organize independently performing tasks, evaluate the correct operation of the work, the reflection of its activities.
Communicative: participate in dialogue in the lesson; Answer the teacher's questions, comrades in the class, to perform in front of the audience using multimedia equipment or other means of demonstration
Planned results
Subject:know - the concepts of "habitat", "Ecology", "Environmental factors" their influence on living organisms, "Living and Non-residential relations";. Be able to determine the concept of "biotic factors"; characterize biotic factors, bring examples.
Personal:express judgments, search and select information; analyze communication, compare, find the answer to the problematic question
MetaPermet: Relations with such academic disciplines as biology, chemistry, physics, geography. Plan actions with the goal; find necessary information in the textbook and reference literature; analyze objects of nature; draw conclusions; Formulate your own opinion.
Form of the organization of educational activities - Individual, group
Teaching methods: illustrative, explanatory, illustrative, partially search, independent work With additional literature and textbook, with the COR.
Receptions:analysis, synthesis, conclusion, translation of information from one species to another, generalization.
Studying a new material
Population dynamics
The population is determined mainly by two phenomena - fertility and mortality
In the process of reproduction, the number of individuals of the population increases, theoretically, it is capable of an unlimited increase in the number (curve 1 in Figure), however, the environmental factors are limited to this growth, and the real curve (curve 2) of the population growth is approaching the value of the maximum number. Pro-journey concluded between the theoretical curve and real, characterizes the resistance of the medium.
Total number The population is susceptible to seasonal, many years of periodic fluctuations in the number, as well as non-riodic (for example, outbreaks of mass reproduction in in-teleca). These changes in numbers are the dynamics of the number of populations.
There are conditional reasons for vibrations of the population number.
If there is an affordable feed, the population number of races, but with its maximum value, feed becomes a limiting factor, and its disadvantage leads to a decrease in the number.
The ups and drops of the population number can occur in the process of competition of several populations due to one ecological niche.
Abiotic factors ( temperature mode, humidity, chimethic composition of the medium, etc.) have a strong influence on the nose of the population and often cause its significant fluctuations.
The population density typically has a certain optimum. With any deviation of the number from this, the optimum mechanisms of its intrapopulation regulation take effect.
The growth of the population density of many insects is accompanied by a decrease in the size of individuals, a decrease in their fertility, an increase in the mortality rate of the larvae and the pupa, the change in the development of the development and the ratio of floors, which sharply reduces the active part of the population. Excessive increase in population density often stimulates cannibalism(from FR. Sapshä1e - cannibal). A vivid example is the phenomenon of eating its own eggs with flour crops. Cannibalism is observed in some fishes, amphibians and other animals. Cannibalism is known for more than 1300 species of animals.
One of the important mechanisms of intraopopulation regulatory number is emigration- Eviction, relocation of the population in less preferred habitats of the same range. In some species, the raising of the population density is accompanied by the appearance of winged individuals capable
settle down. In the overpowering of emigration, a number of mammals occur (especially in mammatic rodents) and birds.
The population density drop is below the optimal level.
(For example, with enhanced rat extermination) causes an increase in fertility and stimulates their earlier puberty.
Some population regulation mechanisms can simultaneously prevent intravidal competition. So, if the bird marks his nesting portion with singing, then another pair of the same type nests beyond. Tags left by many mammals limit their hunting
Plot and warn the interior of other individuals. All this removes intraspecific competition and prevents excessive population sealing.
As I. I. Schmalgausen (1884-1963), all biologists
Systems are characterized by a greater or lesser contribution to self-regulation, T. Homeostasis is the ability of a living system (including populations) to maintain a stable dynamic equilibrium in the changing environment environments. Dynamic equilibrium is called the fluctuation of the population number within some kind of average.
The first attempt to identify the mechanisms of homeostasis in wildlife did K. Linney
(1760). The generalized concept of homeostasis and the term itself suggested W. Kennon (1929).
The homeostatic system is primarily each individual, and
Those already population.
An important mechanism for regulating the number is the stress reaction.
For a person, the phenomenon of stress was first described in 1936. Selre. In response to the negative impact of any factors in the body, two types of reactions occur: specific nature-dependent damaging agent
(for example, increasing heat-product under the action of cold), and a non-specific voltage response (stress) as the general effort of the body to adapt to the changed conditions of nature distinguish many forms of stress:
anthropogenic (occurs in animals under the influence
human activity);
neuropsychic (manifests itself in incompatibility of
Diveumes in the group or as a result of the overpowering of the population);
thermal, noise, etc.
Questions and tasks
1. What is called medium resistance? What is the environmental meaning of this concept?
2. Name the main causes of population fluctuations.
3. Let the characteristic of the population as a self-regulating system. What is called homeostasis population?
Detailed decision Paragraph § 80 in biology for students of grade 10, authors Kamensky A.A., Kriksunov E.A., Book V.V. 2014.
1. What factors affect the number of population?
Answer. In natural systems with low level A species diversity The number of populations is exposed to a strong effect of abiotic and anthropogenic factors. It depends on the weather, chemical composition Environments and degree of its pollution. In systems with a high level of species diversity of population fluctuations, are mainly controlled by biotic factors.
All environmental factors, depending on the nature of their influence on the population, can be divided into two groups.
The factors independent of the population density change the number of populations in one direction, regardless of the number of individuals in them. Abiotic and anthropogenic (with the exception of human environmental activity) factors affect the number of individuals regardless of the population density. So, severe winters Reduce the number of populations of Pyacilline animals (snakes, frogs, lizards). The thick layer of ice and the absence of sufficient oxygen under ice reduce the population of fish in winter. Dry summer and autumn followed by frosty winter reduce the number of colorado beetles populations. Uncontrolled shot of animal or fish fish reduce the restoration possibilities of their populations. High concentrations of pollutants in environment Negatively affect the numbers of all species that are sensitive to them.
The capacity of the medium (maximum population) is determined by the possibility of providing a population with the necessary resources: feed, asylum, features of the opposite sex, etc. When the population is approaching the medium capacity, there is a shortage of feed due to its reinforced remedy. And then the mechanism for regulating the population number through intraspecific competition for the resource is operated. If the population density is high, it regulates the increase in mortality as a result of exacerbation of competition. Part of the individuals die or due to the lack of feed (herbivores), or as a result of a biological or chemical war. Improving mortality leads to a decrease in density. If the population density is low, its replenishment occurs due to an increase in the birth rate due to the resumption of feed resources and weakening competition.
Biological war is the killing of competitors within the population by direct attack (predators of the same type). A sharp decrease in feed resources can lead to the occurrence of cannibalism (eating like this). Chemical war is the allocation chemical substances, delaying growth and development or killing young individuals (plants, aquatic animals). The manifestation of a chemical war can be observed on the example of the development of the headastrics. At high density, larger casuals are isolated in water substances that suppress the growth of small individuals. Therefore, only major casuals are completed. After that, small tadpoles begin to grow.
Regulation of the population number through the number of feed resources is clearly traced on the example of the interaction of populations of the predator and the victim. They have a mutual influence on the number and density of each other, causing repetitive lifts and decals of the number of both populations. Moreover, in this system, the fluctuations in the increase in the number of predator are lagging behind the phase from the increase in the number of victim.
An important mechanism for regulating the number in overpowered populations is a stress response. The increase in the population density leads to an increase in the frequency of meetings between individuals, which causes them physiological changes that lead either to a decrease in fertility, or to an increase in mortality, which causes a decrease in population. Stress does not cause irreversible changes in the body, but only leads to a temporary blocking of some of the functions of the body. When eliminating overpopulation, the ability to reproduce is rapidly restored.
All population density dependent numbers are included before the full exhaustion of the resources of the medium occurs. Due to this, the populations are self-regulation of the number.
2. What examples of cyclic oscillations of population numbers are known to you?
Answer. In nature, populations are experiencing fluctuations. Thus, the number of individual populations of insects and small plants can reach hundreds of thousands and a million individuals. In contrast, the populations of animals and plants can be relatively small in terms of numbers.
Any population cannot consist of a smaller number of individuals than it is necessary to ensure the stable implementation of this medium and the stability of the population to the external environmental factors - the principle of the minimum size of the population.
The minimum population is specific for different species. The output beyond the minimum leads a population to death. Thus, further crossing the Tiger in the Far East will inevitably lead to extinction due to the fact that the remaining units, not finding with a sufficient frequency of partners for reproduction, will be carried out throughout the few generations. It is threatened and rare plants (the Orchid "Venerene Shchemac", etc.).
The population density regulation is carried out when energy and space resources are fully used. A further increase in the population density leads to a decrease in food security and, therefore, to a decrease in fecundity.
Discern non-periodic (rarely observed) and periodic (permanent) fluctuations in the number of natural populations.
Periodic (cyclic) population fluctuations. Trends usually for one season or several years. Cyclic changes with lift lifting on average after 4 years is registered in animals living in the tundra - lemming, polar owls, sand. Seasonal fluctuations in numbers are characteristic of both many insects, miserable rodents, birds, small aquatic organisms.
"There are certain upper and lower limits for the average size of the population, which are observed in nature or which theoretically could exist for an arbitrarily length of time."
Example. At the migratory locust at a low number of the larva, a single phase have a bright green color, and adults are gray-green color. During the years of mass reproduction, the locust passes into the stadium phase. The larvae acquire bright yellow with black stains in color, and adults are lemon yellow. Morphology of individuals changes.
Questions after § 80
1. What is the dynamics of the population?
Answer. The dynamics of the population is the processes of changes in its basic biological indicators in time. The main importance in the study of the dynamics of the population is given changes in the number, biomass and population structure. The dynamics of the population is one of the most significant biological and environmental phenomena. It can be said that the life of the population is manifested in its dynamics.
The population cannot exist without constant changes, at the expense of which it adapts to changing living conditions. Indicators such as fertility, mortality and age structure are very important, but no one cannot judge the dynamics of the population as a whole.
An important process of population dynamics is the increase in the number (or simply "population growth"), which occurs when the organisms are mastering new habitats or after the disaster suffered. The nature of growth is different. In populations with a simple age structure, the growth is fast, explosive. In populations with a complex age structure, he smooth, gradually slowing down. In any case, the population density increases until the factors that limit the increase in population increase are beginning (the limitation may be associated with the full use of resource-consumed by the population or other types of restrictions). In the end, an equilibrium is achieved, which is preserved.
2. What is the phenomenon of regulating populations? What value does it have in the ecosystem?
Answer. When the population growth is completed, its number begins to fluctuations around some more or less permanent value. Often these oscillations are caused by seasonal or annual changes in living conditions (for example, changes in temperature, humidity, food supply). Sometimes they can be viewed as random.
In some populations, the fluctuations of the number are the right cyclic nature.
The most famous examples of cyclic oscillations include fluctuations in the number of certain mammalian species. For example, cycles of three- and four-year periodicity are characteristic of many mice-like rodents (mice of pools, lemming) and their predators (polar owls, sands).
The most famous example of cyclic fluctuations in the number of insects is periodic outbreaks of the locust. Information about the invasion of the wandering locust goes back to distant antiquity. Lokchalcha lives in deserts and curtail areas. For many years, it does not make migrations, does not harm sow and does not particularly attract attention. However, from time to time the density of locust populations reaches a monstrous size. Under the influence of crowdability, insects undergo a number of changes in their appearance (for example, they develop longer wings) and begin to fly to agricultural areas, eating everything in their path. The causes of such population explosions are apparently due to the instability of environmental conditions.
3. What role does abiotic and biotic factors play in the change in population density?
Answer. The causes of sharp fluctuations in the number of populations of certain organisms can be various abiotic and biotic factors. Sometimes these oscillations are well consistent with change climatic conditions. However, in some cases, the influence of external factors it is impossible to explain changes in the number of one or another population. The reasons that cause vibrations of population numbers may be in themselves; Then they talk about the internal factors of population dynamics.
There are cases when, in terms of overpopulation, a number of mammals occur sharp changes in the physiological state. Such changes primarily affect the neuroendocrine system organs, affecting the behavior of animals, changing their resistance to diseases and various types of stress.
Sometimes it leads to increased mortality of individuals and a decrease in the density of the population. Cheers-Belyaki, for example, during the periods of the peak of the number often suddenly die from the so-called "shock disease".
Such mechanisms will undoubtedly be attributed to the internal regulators of the number. They triggered automatically as soon as the density exceeds some threshold value.
In general, all factors affecting the number of population (no matter that limiting or conducive to reproduction of the population) is divided into two large groups:
- independent population density;
- depending on the density of the population.
The second group of factors is often referred to as regulatory or controlling density.
It should not be thought that the presence of regulatory mechanisms should always stabilize the number. In some cases, their effects can lead to cyclic fluctuations in numbers even under constant living conditions.
Tell us about the seasonal changes in the population of animals and plants (remember personal observations).
Answer. In many species of animals and plants, the fluctuations in population numbers are caused by seasonal changes in living conditions (temperature, humidity, light, food supply, etc.). Examples of seasonal vibrations of population numbers demonstrate - flocks of mosquitoes, migratory birds, annual herbs - in the warm season, in winter These phenomena are practically reduced.
The greatest interest, represent the fluctuations in the number of populations that occur from year to year. They are called inter-annual unlike in-country, or seasonal. The interannual dynamics of population numbers may have a different character and manifest itself in the form of smooth waves of changes (numbers, biomass, population structure) or in the form of frequent jump-shaking changes.
And in that and in different cases, these changes can be regular, that is, cyclic, or irregular - chaotic. The first in contrast to the second contain elements that are repeated at equal intervals (for example, every 10 years the population has reaches a certain maximum value).
Observed from year to year fluctuations in the number of certain types of birds (for example, a city sparrow) or fish (bleak, ripping, bulls, etc.) give an example of irregular changes in the magnitude of the population associated, as a rule, with changes in climatic conditions, or with changes in environmental pollution habitats with substances that have a destructive effect on organisms.
Interesting surveillance of fluctuations in the city of Big Tits. Its number in the city in winter increases 10 times compared with the summer.
Using additional literature, give examples of cyclic oscillations of animal or plants.
Answer. For natural populations distinguish:
1) seasonal changes in the number associated with seasonal changes in environmental factors,
2) fluctuations that are caused by pushing changes. Seasonal changes in numbers are most brightly manifested in many insects, as well as most annual plants.
Examples of significant numbering oscillations demonstrate some types of northern mammals and birds, which have either 9-10- or 3-4-year cycles. The classic example of 9-10-year-old oscillations is the change in the number of hare-beyak and lynx in Canada, and the peaks of the hare's number for the year or more preceded the peaks of the flow of the lynx.
To assess the dynamic state of plant populations, an analysis of age-related (ontogenetic) states is carried out. The most simply defined feature of the stable state of the population is a complete ontogenetic spectrum. Such spectra are called basic (characteristic), they determine the definitive (dynamically sustainable) state of populations.
The most famous examples of cyclic oscillations include joint oscillations of the number of certain types of northern mammals. For example, cycles of three- and four-year periodicity are characteristic of many northern mysterious rodents (mice, fields, lemming) and their predators (polar owls, sands), as well as hares and lynx.
In Europe, the lemmings sometimes achieve such a high density that they begin to migrate from their overcrowded habitats. Both lemming, and locusts, not every case of increasing numbers is accompanied by migration.
Sometimes cyclic vibrations of population numbers can be explained by complex interactions between populations of various types of animals and plants in communities.
Consider as an example of oscillation of the number of certain types of insects in European forests, such as butterflies of pine spin and larch leaflerting, the larvae of which feed on the leaves of trees. The peaks of the number are repeated from them in about 4-10 years.
The fluctuations in the number of these species are determined by both the dynamics of the biomass of trees, and vibrations of the number of birds that feed insects. As the biomass of trees in the forest increase the largest and old trees in the forest become susceptible to the caterpillars of the craders leaflers and often die from the repeating defoliation (the disappearance of leaves).
Returning and wood decomposition returns to forest ground nutrients. They are used for their development young trees, less sensitive to the attack of insects. The growth of young trees contributes to an increase in illumination due to the death of old trees with large crowns. In the meantime, the birds reduce the number of cleaners. However, as a result of the growth of trees, it (number) again begins to increase and the process is repeated.
If we consider existence coniferous forests In large intervals, it becomes clear that the leafer periodically, as if rejuvenates the ecosystem of the coniferous forest, is an integral part of it. Therefore, the increase in the number of this butterfly is not a catastrophe, as it may seem to anyone who sees the dead and dying trees at a certain stage of the cycle.
The causes of sudden oscillations of the number of some populations can be various abiotic and biotic factors. Sometimes these oscillations are well consistent with changes in climatic conditions. However, in some cases, the influence of external factors it is impossible to explain changes in the number of one or another population. The reasons that cause vibrations of population numbers may be in themselves; Then they talk about the internal factors of population dynamics
