Introduction

In this work I will cover in detail the topic “Limiting factors”. I will consider their definition, types, laws and examples.

Different environmental factors have different significance for living organisms.

For organisms to live, a certain combination of conditions is necessary. If all environmental conditions are favorable, with the exception of one, then this condition becomes decisive for the life of the organism in question.

Of the variety of limiting environmental factors, the attention of researchers is primarily attracted to those that inhibit the vital activity of organisms and limit their growth and development.

Main part

In the total pressure of the environment, factors are identified that most strongly limit the success of the life of organisms. Such factors are called limiting or limiting.

Limiting factors - This

1) any factors inhibiting population growth in the ecosystem; 2) environmental factors, the value of which greatly deviates from the optimum.

In the presence of optimal combinations of many factors, one limiting factor can lead to oppression and death of organisms. For example, heat-loving plants die at negative air temperatures, despite the optimal content of nutrients in the soil, optimal humidity, light, and so on. Limiting factors are irreplaceable if they do not interact with other factors. For example, a lack of mineral nitrogen in the soil cannot be compensated for by an excess of potassium or phosphorus.

Limiting factors for terrestrial ecosystems:

Temperature;

Nutrients in the soil.

Limiting factors for aquatic ecosystems:

Temperature;

Sunlight;

Salinity.

Typically, these factors interact in such a way that one process is limited simultaneously by several factors, and a change in any of them leads to a new equilibrium. For example, an increase in food availability and a decrease in predation pressure can lead to an increase in population size.

Examples of limiting factors are: outcrops of uneroded rocks, erosion base, valley sides, etc.

Thus, the factor limiting the spread of deer is the depth of the snow cover; moths of the winter armyworm (a pest of vegetable and grain crops) - winter temperature, etc.

The idea of ​​limiting factors is based on two laws of ecology: the law of the minimum and the law of tolerance.

Law of the minimum

In the mid-19th century, the German organic chemist Liebig, studying the effect of various microelements on plant growth, was the first to establish the following: plant growth is limited by an element whose concentration and significance is at a minimum, that is, present in a minimal amount. The so-called “Liebig barrel” helps to represent the law of the minimum figuratively. This is a barrel with wooden slats of different heights, as shown in the picture.

. It is clear that no matter what the height of the other slats, you can pour exactly as much water into the barrel as the height of the shortest slats. Likewise, a limiting factor limits the life activity of organisms, despite the level (dose) of other factors. For example, if yeast is placed in cold water, the low temperature will become a limiting factor for its reproduction. Every housewife knows this, and therefore leaves the yeast to “swell” (and actually multiply) in warm water with a sufficient amount of sugar.

Heat, light, water, oxygen, and other factors can limit or limit the development of organisms, if their movement corresponds to the ecological minimum. For example, the tropical fish angelfish dies if the water temperature drops below 16 °C. And the development of algae in deep-sea ecosystems is limited by the depth of penetration of sunlight: there are no algae in the bottom layers.

Later (in 1909), the law of the minimum was interpreted by F. Blackman more broadly, as the action of any ecological factor that is at a minimum: environmental factors that have the worst significance in specific conditions especially limit the possibility of the existence of a species in these conditions in spite of and in spite of optimal combination of other hotel conditions.

In its modern formulation, the law of the minimum sounds like this: the body's endurance is determined by the weakest link in the chain of its environmental needs .

To successfully apply the law of limiting factors in practice, two principles must be observed:

The first is restrictive, that is, the law is strictly applicable only under stationary conditions, when the inflow and outflow of energy and substances are balanced. For example, in a certain body of water, the growth of algae is limited under natural conditions by a lack of phosphates. Nitrogen compounds are found in excess in water. If wastewater with a high content of mineral phosphorus begins to be discharged into this reservoir, the reservoir may “bloom.” This process will progress until one of the elements is used up to the restrictive minimum. Now it may be nitrogen if phosphorus continues to be supplied. At the transition moment (when there is still enough nitrogen and enough phosphorus), the minimum effect is not observed, i.e., none of these elements affects the growth of algae.

The second takes into account the interaction of factors and the adaptability of organisms. Sometimes the body is able to replace the deficient element with another, chemically similar one. Thus, in places where there is a lot of strontium, in mollusk shells it can replace calcium when there is a deficiency of the latter. Or, for example, the need for zinc in some plants is reduced if they grow in the shade. Therefore, a low zinc concentration will limit plant growth less in the shade than in bright light. In these cases, the limiting effect of even an insufficient amount of one or another element may not manifest itself.

Law of Tolerance

The concept that, along with a minimum, a maximum can also be a limiting factor was introduced 70 years later in 1913 after Liebig by the American zoologist W. Shelford. He drew attention to the fact that not only those environmental factors whose values ​​are minimal, but also those that are characterized by an ecological maximum can limit the development of living organisms, and formulated the law of tolerance: “ The limiting factor for the prosperity of a population (organism) can be either a minimum or a maximum of environmental impact, and the range between them determines the amount of endurance (tolerance limit) or the ecological valency of the organism to this factor)" (Fig. 2).

Figure 2 - Dependence of the result of an environmental factor on its intensity

The favorable range of action of an environmental factor is called optimum zone (normal life activities). The more significant the deviation of a factor’s action from the optimum, the more this factor inhibits the vital activity of the population. This range is called zone of oppression or pessimism . The maximum and minimum transferable values ​​of a factor are critical points beyond which the existence of an organism or population is no longer possible. The tolerance limit describes the amplitude of factor fluctuations, which ensures the most fulfilling existence of the population. Individuals may have slightly different tolerance ranges.

Later, tolerance limits for various environmental factors were established for many plants and animals. The laws of J. Liebig and W. Shelford helped to understand many phenomena and the distribution of organisms in nature. Organisms cannot be distributed everywhere because populations have a certain tolerance limit in relation to fluctuations in environmental environmental factors.

Many organisms are capable of changing tolerance to individual factors if conditions change gradually. You can, for example, get used to the high temperature of the water in the bath if you get into warm water and then gradually add hot water. This adaptation to a slow change in factor is a useful protective property. But it can also be dangerous. Unexpectedly, without warning signs, even a small change can be critical. A threshold effect occurs: the last straw could be fatal. For example, a thin twig can cause a camel's already overloaded back to break.

The principle of limiting factors is valid for all types of living organisms - plants, animals, microorganisms and applies to both abiotic and biotic factors. For example, competition from another species may become a limiting factor for the development of organisms of a given species. In agriculture, pests and weeds often become the limiting factor, and for some plants the limiting factor in development is the lack (or absence) of representatives of another species. In accordance with the law of tolerance, any excess of matter or energy turns out to be a pollutant. Thus, excess water, even in arid areas, is harmful, and water can be considered a common pollutant, although it is essential in optimal quantities. In particular, excess water prevents normal soil formation in the chernozem zone.

Limiting factors are conditions that go beyond the body's endurance. They limit any manifestation of its functions. Let us consider further the limiting effect of factors in more detail.

general characteristics

Features of influence

When considering the theory of minimums, one should not confuse leading and limiting environmental factors, since the latter can be both major and secondary. The limiting condition is usually the one that deviates the farthest from the norm. If the indicators are beyond the limits of sustainability, regardless of whether they have changed towards the minimum or towards the maximum, they turn into limiting factors. This also occurs in cases where all other conditions are favorable or optimal.

Shelford's limiting factors

The theory discussed above received its development 70 years later. The American scientist Shelford found that not only an element present in minimal concentration can affect the development of the body, but its excess can also cause adverse consequences. For example, both excessive and insufficient amounts of water will be harmful to the plant. In the latter case, acidification of the soil will occur, and in the former, the assimilation of nutritional compounds will be difficult. Many organisms are negatively affected by changes in pH levels and other limiting factors. Tolerance, within which normal existence is possible, is limited, in fact, by a deficiency or excess of conditions, the indicators of which can be close to the limits of tolerance.

Endurance Range

Tolerance limits are not constant. For example, the range may narrow if a condition approaches one or another boundary. This situation also occurs during the reproduction of organisms, when many indicators become limiting. It follows from this that the influence of many limiting environmental factors is variable. This means that one condition may or may not be oppressive or limiting.

Acclimatization

At the same time, it should be remembered that organisms themselves are able to reduce the negative impact by creating, for example, a certain microclimate. In this case, some kind of compensation of conditions appears. It is most effective at the community level. With such compensation, conditions are formed for the physiological adaptation of the species - eurybiote, which is widespread. Acclimatizing in a certain territory, it forms a unique ecotype, a population, the tolerance limits of which correspond to the locality. Deeper adaptation processes can contribute to the formation of genetic races.

Putting theory into practice

To have the clearest idea of ​​how limiting environmental factors influence organisms, we can take as an example the development of plants under the influence of carbon dioxide. Its content in the air is low, so even a slight fluctuation in its level will be of great importance for plantings. Carbon dioxide is a product of the respiration of plants and animals, the combustion of organic substances, the activity of volcanoes, etc. Its content depends not only on the nature of the location of its sources and the number of consumers. It also changes over time. Thus, in winter and autumn, the concentration of carbon dioxide is increased due to differences in the photosynthetic activity of green spaces. Moreover, in summer, with intensive assimilation of plants, its amount decreases significantly. Fluctuations in CO 2 in the air have a significant impact on the activity of photosynthesis and the level of plant nutrition. Even small changes have a negative impact on their development and growth, appearance, and internal processes. The usual CO 2 content in the air, close to 0.03%, is not considered optimal for normal plant life. In this regard, a high degree of intensity of photosynthesis can be achieved either by the rapid movement of various masses, which will ensure its influx to the assimilating parts, or through the activity of heterotrophs, whose reproduction is accompanied by its release.

Illumination and temperature

Let's consider how limiting factors can influence the dandelion phenotype. Due to the significant variability of its specimens, which grow in well-lit areas, the plant has predominantly features of light-loving plantings. In particular, they differ:

• Thick, small, fleshy leaf blades with dense veining.
• Branched root system.
• The location of the leaves at an angle relative to the sun's rays.
• A peculiar movement that provides protection from excessive lighting.

At the same time, dandelions that grow in the shade have the following characteristics:

• Poorly developed root system.
• Large, wide, thin leaves with sparse veining, located perpendicular to the rays, etc.

When analyzing sections of leaf blades of the first and second types of dandelion, deeper histological differences can be detected, which complement the morphological characteristics discussed above. The influence of temperature fluctuations is also quite clearly visible. Moreover, if transformation with changes in illumination can be observed by comparing different specimens, then in this case it can be seen on one plant. At low spring temperatures from +4 to +6 degrees, early, heavily cut leaves form on the plants. If you transfer a dandelion in this form to a greenhouse, where the temperature is +15...+18 degrees, plates with solid edges will begin to develop. When placing the plant in intermediate conditions, the leaves will have slight rugosity.

Chain reaction

One of the significant additions to the considered theory is the proposition that a change in any condition gives rise to far-reaching consequences. Currently, it is almost impossible to find an area on the planet where there are no limiting factors. In many cases, the activity of the person himself creates limiting or oppressive conditions. One such striking example is the complete extermination of huge populations of the Steller's sea cow. This process took a person relatively little time - a few years - in comparison with the almost century-long period of natural restoration of the ecosystem.

Surely each of us has noticed how plants of the same species develop well in the forest, but do not feel well in open spaces. Or, for example, some mammal species have large populations while others are more limited under seemingly identical conditions. All life on Earth is one way or another subject to its own laws and rules. Ecology studies them. One of the fundamental statements is Liebig's law of minimum

Limiting what is it?

The German chemist and founder of agricultural chemistry, Professor Justus von Liebig, made many discoveries. One of the most famous and recognized is the discovery of the fundamental limiting factor. It was formulated in 1840 and later expanded and generalized by Shelford. The law states that for any living organism, the most significant factor is the one that deviates the most from its optimal value. In other words, the existence of an animal or plant depends on the degree of severity (minimum or maximum) of a particular condition. Individuals encounter a wide variety of limiting factors throughout their lives.

"Liebig's Barrel"

The factor limiting the life activity of organisms can be different. The formulated law is still actively used in agriculture. J. Liebig established that plant productivity depends primarily on the mineral substance (nutrient), which is most poorly expressed in the soil. For example, if nitrogen in the soil is only 10% of the required norm, and phosphorus is 20%, then the factor limiting normal development is the lack of the first element. Therefore, nitrogen-containing fertilizers should be initially applied to the soil. The meaning of the law was stated as clearly and clearly as possible in the so-called “Liebig barrel” (pictured above). Its essence is that when the vessel is filled, water begins to overflow where the shortest board is, and the length of the rest no longer matters much.

Water

This factor is the most stringent and significant compared to the others. Water is the basis of life, as it plays an important role in the life of an individual cell and the entire organism as a whole. Maintaining its quantity at the proper level is one of the main physiological functions of any plant or animal. Water as a factor limiting life activity is due to the uneven distribution of moisture over the Earth’s surface throughout the year. In the process of evolution, many organisms have adapted to the economical use of moisture, surviving the dry period in a state of hibernation or dormancy. This factor is most strongly expressed in deserts and semi-deserts, where flora and fauna are very sparse and unique.

Light

Light arriving in the form of solar radiation powers all life processes on the planet. Organisms care about its wavelength, duration of exposure, and radiation intensity. Depending on these indicators, the body adapts to environmental conditions. As a factor limiting existence, it is especially pronounced at great sea depths. For example, plants are no longer found at a depth of 200 m. Together with lighting, at least two more limiting factors “work” here: pressure and oxygen concentration. This can be contrasted with the tropical rainforests of South America, as the most favorable territory for life.

Ambient temperature

It's no secret that all physiological processes occurring in the body depend on external and internal temperature. Moreover, most species are adapted to a rather narrow range (15-30 °C). The dependence is especially pronounced in organisms that are not able to independently maintain a constant body temperature, for example, reptiles. In the process of evolution, many adaptations have been formed that allow one to overcome this limited factor. So, in hot weather, in order to avoid overheating, it intensifies in plants through stomata, in animals - through the skin and respiratory system, as well as behavioral characteristics (hiding in the shade, burrows, etc.).

Pollutants

The significance cannot be underestimated. The last few centuries for humans have been marked by rapid technical progress and the rapid development of industry. This has led to harmful emissions into water bodies, soil and the atmosphere increasing several times. It is possible to understand which factor limits this or that species only after research. This state of affairs explains the fact that the species diversity of individual regions or areas has changed beyond recognition. Organisms change and adapt, some replace others.

All these are the main factors limiting life. In addition to them, there are many others, which are simply impossible to list. Each species and even individual is individual, therefore the limiting factors will be very diverse. For example, the percentage of oxygen dissolved in water is important for trout; for plants, the quantitative and qualitative composition of pollinating insects, etc.

All living organisms have certain limits of endurance due to one or another limiting factor. Some are quite wide, others are narrow. Depending on this indicator, eurybionts and stenobionts are distinguished. The former are able to tolerate a large amplitude of fluctuations of various limiting factors. For example, living everywhere from the steppes to the forest-tundra, wolves, etc. Stenobionts, on the contrary, are able to withstand very narrow fluctuations, and these include almost all rain forest plants.

In this work I will cover in detail the topic “Limiting factors”. I will consider their definition, types, laws and examples.

Different environmental factors have different significance for living organisms.

For organisms to live, a certain combination of conditions is necessary. If all environmental conditions are favorable, with the exception of one, then this condition becomes decisive for the life of the organism in question.

Of the variety of limiting environmental factors, the attention of researchers is primarily attracted to those that inhibit the vital activity of organisms and limit their growth and development.

Main part

In the total pressure of the environment, factors are identified that most strongly limit the success of the life of organisms. Such factors are called limiting or limiting.

Limiting factors - This

1) any factors inhibiting population growth in the ecosystem; 2) environmental factors, the value of which greatly deviates from the optimum.

In the presence of optimal combinations of many factors, one limiting factor can lead to oppression and death of organisms. For example, heat-loving plants die at negative air temperatures, despite the optimal content of nutrients in the soil, optimal humidity, light, and so on. Limiting factors are irreplaceable if they do not interact with other factors. For example, a lack of mineral nitrogen in the soil cannot be compensated for by an excess of potassium or phosphorus.

Limiting factors for terrestrial ecosystems:

Temperature;

Nutrients in the soil.

Limiting factors for aquatic ecosystems:

Temperature;

Sunlight;

Salinity.

Typically, these factors interact in such a way that one process is limited simultaneously by several factors, and a change in any of them leads to a new equilibrium. For example, an increase in food availability and a decrease in predation pressure can lead to an increase in population size.

Examples of limiting factors are: outcrops of uneroded rocks, erosion base, valley sides, etc.

Thus, the factor limiting the spread of deer is the depth of the snow cover; moths of the winter armyworm (a pest of vegetable and grain crops) - winter temperature, etc.

The idea of ​​limiting factors is based on two laws of ecology: the law of the minimum and the law of tolerance.

Law of the minimum

In the mid-19th century, the German organic chemist Liebig, studying the effect of various microelements on plant growth, was the first to establish the following: plant growth is limited by an element whose concentration and significance is at a minimum, that is, present in a minimal amount. The so-called “Liebig barrel” helps to represent the law of the minimum figuratively. This is a barrel with wooden slats of different heights, as shown in the figure. It is clear that no matter what the height of the other slats, you can pour exactly as much water into the barrel as the height of the shortest slats. Likewise, a limiting factor limits the life activity of organisms, despite the level (dose) of other factors. For example, if yeast is placed in cold water, the low temperature will become a limiting factor for its reproduction. Every housewife knows this, and therefore leaves the yeast to “swell” (and actually multiply) in warm water with a sufficient amount of sugar.

Heat, light, water, oxygen, and other factors can limit or limit the development of organisms, if their movement corresponds to the ecological minimum. For example, the tropical fish angelfish dies if the water temperature drops below 16 °C. And the development of algae in deep-sea ecosystems is limited by the depth of penetration of sunlight: there are no algae in the bottom layers.

Later (in 1909), the law of the minimum was interpreted by F. Blackman more broadly, as the action of any ecological factor that is at a minimum: environmental factors that have the worst significance in specific conditions especially limit the possibility of the existence of a species in these conditions in spite of and in spite of optimal combination of other hotel conditions.

In its modern formulation, the law of the minimum sounds like this: the body's endurance is determined by the weakest link in the chain of its environmental needs .

To successfully apply the law of limiting factors in practice, two principles must be observed:

The first is restrictive, that is, the law is strictly applicable only under stationary conditions, when the inflow and outflow of energy and substances are balanced. For example, in a certain body of water, the growth of algae is limited under natural conditions by a lack of phosphates. Nitrogen compounds are found in excess in water. If wastewater with a high content of mineral phosphorus begins to be discharged into this reservoir, the reservoir may “bloom.” This process will progress until one of the elements is used up to the restrictive minimum. Now it may be nitrogen if phosphorus continues to be supplied. At the transition moment (when there is still enough nitrogen and enough phosphorus), the minimum effect is not observed, i.e., none of these elements affects the growth of algae.

The second takes into account the interaction of factors and the adaptability of organisms. Sometimes the body is able to replace the deficient element with another, chemically similar one. Thus, in places where there is a lot of strontium, in mollusk shells it can replace calcium when there is a deficiency of the latter. Or, for example, the need for zinc in some plants is reduced if they grow in the shade. Therefore, a low zinc concentration will limit plant growth less in the shade than in bright light. In these cases, the limiting effect of even an insufficient amount of one or another element may not manifest itself.

Law of Tolerance

The concept that, along with a minimum, a maximum can also be a limiting factor was introduced 70 years later in 1913 after Liebig by the American zoologist W. Shelford. He drew attention to the fact that not only those environmental factors whose values ​​are minimal, but also those that are characterized by an ecological maximum can limit the development of living organisms, and formulated the law of tolerance: “ The limiting factor for the prosperity of a population (organism) can be either a minimum or a maximum of environmental impact, and the range between them determines the amount of endurance (tolerance limit) or the ecological valency of the organism to this factor)" (Fig. 2).

Figure 2 - Dependence of the result of an environmental factor on its intensity

The favorable range of action of an environmental factor is called optimum zone (normal life activities). The more significant the deviation of a factor’s action from the optimum, the more this factor inhibits the vital activity of the population. This range is called zone of oppression or pessimism . The maximum and minimum transferable values ​​of a factor are critical points beyond which the existence of an organism or population is no longer possible. The tolerance limit describes the amplitude of factor fluctuations, which ensures the most fulfilling existence of the population. Individuals may have slightly different tolerance ranges.

Later, tolerance limits for various environmental factors were established for many plants and animals. The laws of J. Liebig and W. Shelford helped to understand many phenomena and the distribution of organisms in nature. Organisms cannot be distributed everywhere because populations have a certain tolerance limit in relation to fluctuations in environmental environmental factors.

Many organisms are capable of changing tolerance to individual factors if conditions change gradually. You can, for example, get used to the high temperature of the water in the bath if you get into warm water and then gradually add hot water. This adaptation to a slow change in factor is a useful protective property. But it can also be dangerous. Unexpectedly, without warning signs, even a small change can be critical. A threshold effect occurs: the last straw could be fatal. For example, a thin twig can cause a camel's already overloaded back to break.

The principle of limiting factors is valid for all types of living organisms - plants, animals, microorganisms and applies to both abiotic and biotic factors. For example, competition from another species may become a limiting factor for the development of organisms of a given species. In agriculture, pests and weeds often become the limiting factor, and for some plants the limiting factor in development is the lack (or absence) of representatives of another species. In accordance with the law of tolerance, any excess of matter or energy turns out to be a pollutant. Thus, excess water, even in arid areas, is harmful, and water can be considered a common pollutant, although it is essential in optimal quantities. In particular, excess water prevents normal soil formation in the chernozem zone.

The following was found:

· organisms with a wide range of tolerance to all factors are widespread in nature and are often cosmopolitan, for example, many pathogenic bacteria;

· Organisms may have a wide range of tolerance for one factor and a narrow range for another. For example, people are more tolerant to the absence of food than to the lack of water, i.e., the tolerance limit for water is narrower than for food;

· if conditions for one of the environmental factors become suboptimal, then the tolerance limit for other factors may also change. For example, when there is a lack of nitrogen in the soil, cereals require much more water;

· the limits of tolerance in breeding individuals and offspring are less than in adult individuals, i.e. females during the breeding season and their offspring are less hardy than adult organisms. Thus, the geographic distribution of game birds is more often determined by the influence of climate on eggs and chicks, rather than on adult birds. Caring for offspring and careful attitude towards motherhood are dictated by the laws of nature. Unfortunately, sometimes social “achievements” contradict these laws;

· extreme (stressful) values ​​of one of the factors lead to a decrease in the tolerance limit for other factors. If heated water is released into a river, fish and other organisms spend almost all their energy coping with stress. They lack energy to obtain food, protect themselves from predators, and reproduce, which leads to gradual extinction. Psychological stress can also cause many somatic (gr. soma- body) diseases not only in humans, but also in some animals (for example, dogs). With stressful values ​​of the factor, adaptation to it becomes more and more “expensive”.

It is possible to identify probable weak links in the environment that may turn out to be critical or limiting. With targeted influence on limiting conditions, it is possible to quickly and effectively increase plant yields and animal productivity. Thus, when growing wheat on acidic soils, no agronomic measures will be effective unless liming is used, which will reduce the limiting effect of acids. Or, if you grow corn in soils that are very low in phosphorus, even with enough water, nitrogen, potassium and other nutrients, it will stop growing. Phosphorus in this case is the limiting factor. And only phosphorus fertilizers can save the harvest. Plants can also die from too much water or excess fertilizer, which in this case are also limiting factors.

If a change in the value of the limiting factor leads to a much larger (in compared units) change in the output characteristics of the system or other elements, then the limiting factor is called control element in relation to these latter controlled characteristics, or elements.

Often a good way to identify limiting factors is to study the distribution and behavior of organisms on the periphery of their range. If we agree with the statement of Andrevarta and Birch (1954) that distribution and abundance are controlled by the same factors, then studying the periphery of the range should be doubly useful. However, many ecologists believe that the abundance in the center of the range and the distribution on its periphery can be controlled by completely different factors, especially since, as geneticists have discovered, individuals in peripheral populations may differ from individuals in central populations at the genotype level.

Conclusion

In this work, I examined in detail the definition, types, laws and examples of limiting factors.

After analyzing the work, I drew conclusions.

Identification of limiting factors is an approximation technique that reveals the roughest, most significant features of the system.

Identification of limiting links allows one to significantly simplify the description, and in some cases, to qualitatively judge the dynamic states of the system.

Knowledge of limiting factors provides the key to ecosystem management, so only skillful regulation of living conditions can give effective management results.

The concept of limiting factors, originating from the classical works of Liebig, is actively used in biochemistry, physiology, agronomy, as well as in quantitative genetics.

A key role in evolution is played by limiting factors of organization that limit the possibilities of certain directions of evolution.

The value of the concept of limiting factors is that it provides a starting point for exploring complex situations.

Identifying limiting factors is the key to controlling the life activity of organisms.

Identification of limiting factors is very important for many activities, especially agriculture.

Bibliography

1.Ecology. Textbook for universities

2.Ecology. Textbook for universities. Author: Korobkin V.I., Peredelsky L.V. Publisher: Phoenix, 2010
3. Markov M.V. Agrophytocenology. Ed. Kazan University, 1972.
4. Nebel B. Environmental Science. M.: Mir, 1993.
5. Ricklefs R. Fundamentals of General Ecology. M.: Mir. 1979.
6. Soviet encyclopedic dictionary. M.: Soviet Encyclopedia, 1988.
7. Encyclopedic dictionary of environmental terms. Kazan, 2001.

Anthropogenic factors

These are forms of activity of human society that change the habitat for a variety of organisms.

Anthropogenic factors usually act indirectly, by changing the action of abiotic and biotic factors.

For example, thinning in coniferous-broad-leaved forests creates favorable conditions for most small passerine birds, but cutting down hollow trees reduces the number of hollow nesters (owls, flycatchers)

At the same time, great and direct impact of anthropogenic factors: deforestation, poaching.

The influence of environmental factors on a living organism is very diverse. Some factors have a stronger influence, others have a weaker effect; some influence all aspects of life, others influence a particular life process. Nevertheless, in the nature of their impact on organisms and in the responses of living beings, a number of general patterns can be identified that fit into a certain general scheme of the action of an environmental factor on the life activity of an organism.

The abscissa axis shows the intensity of the factor (for example, temperature, illumination, salt concentration in the soil solution, soil moisture, etc.), and the ordinate axis shows the body’s response to the environmental factor in its quantitative expression (for example, the intensity of photosynthesis, respiration, growth . The size of the organism or its organs, the number of individuals per unit area, etc.). The range of action of an environmental factor is limited by the corresponding extreme threshold values ​​(minimum and maximum points) of a given factor, at which the existence of an organism is still possible. The limits between critical points are called the ecological valency of living beings in relation to a specific environmental factor. The values ​​of the environmental factor that are most favorable for a given species are called optimal, or simply an ecological optimum . The same factor values ​​that are unfavorable for a given species are called maximum or simply ecological pessimum .

Different types of living organisms differ markedly from each other both in the position of the optimum and in the ecological valence. For example, arctic foxes in the tundra can tolerate fluctuations in air temperature in the range of about 80 0 C (from +30 to -55 0 C), while warm-water crustaceans Corilia mirabilis can withstand changes in water temperature in the range of no more than 6 0 C (from 23 to 29 0 C), and the filamentous cyanobacterium oscillatorium, living on the island. Java in water with a temperature of 64 0 C, dies at 68 0 C after 5-10 minutes. In the same way, some meadow grasses prefer soils with a rather narrow range of acidity (for example, common heather, sorrel, and white grass serve as indicators of acidic soils with a pH of 3.5-4.5), others grow well over a wide pH range - from strongly acidic to alkaline ( for example, Scots pine). Types of organisms whose existence requires strictly defined, relatively constant environmental conditions are called stenobiont , and those that have a broad environmental valency in relation to a complex of factors - eurybiont . In this case, a species may have a narrow amplitude in relation to one factor and a wide amplitude in relation to another (for example, it can be confined to a narrow range of temperatures and a wide range of salinity). In addition, the same strength of manifestation of a factor can be optimal for one species, pessimal for another, and beyond the limits of endurance for a third.

The survival rate of organs reaches a maximum at average values ​​of this environmental factor.

The ability of a species to reproduce individuals and to compete with others will be limited by the factor that most strongly deviates from its optimal value. If the quantitative value of at least one of the factors goes beyond the limits of endurance, then the existence of the species becomes impossible, no matter how favorable the other conditions are.

Such factors that go beyond the maximum or minimum are called limiting. For example, the distribution of many animals and plants to the north is usually limited by a lack of heat, while in the south the limiting factor for the same species may be a lack of moisture or essential food. Limiting environmental factors also determine the geographic range of a species.

Adaptations of organisms to the seasonal rhythm of external conditions.

Climate is one of the main components of the natural environment. For the life of terrestrial plants and animals, climate components such as light, temperature and humidity are of greatest importance. An important feature of these factors is their natural change throughout the year and day, and in connection with geographic zoning. Therefore, adaptations to them are zonal and seasonal.

Seasonal periodicity is one of the most common phenomena in living nature. It is especially pronounced at measured latitudes. The basis of the external simple and well-known seasonal phenomena in the world of organs are complex adaptive reactions of a rhythmic nature, which were discovered relatively recently.

As an example, consider seasonal periodicity in the central regions of our country. Here, the annual temperature variation is of leading importance for plants and animals. The period favorable for life lasts about six months.

Signs of spring appear as soon as the snow melts: willow, alder, and hazel bloom, plant sprouts appear, migratory birds arrive. At this time, even slight frosts damage plants and cause the death of many insects.

In midsummer, despite the temperature and abundance of precipitation, the growth of many plants slows down. Reproduction in birds ends.

The second half of summer and early autumn is the period of ripening of fruits and seeds in most plants and accumulation of nutrients in their tissues. At the same time, signs of preparation for winter are already visible. Overwintering buds form and shoots on trees become lignified; there is an increased outflow of nutrients from the leaves to the stems and roots. Autumn molting begins in birds and mammals, and migratory birds gather in flocks.

Preparation for winter ends with the falling of plant leaves, the flight of many birds, the disappearance of insects that hide and die. Even before the onset of stable frosts, a period of winter dormancy begins in nature.

The state of winter dormancy is especially pronounced among organisms that are unable to maintain a constant body temperature, i.e. in plants, all invertebrates and lower vertebrates.

Winter dormancy is not just a cessation of development caused by low temperature, but a very complex physiological adaptation. In each species, the state of winter dormancy occurs only at a certain stage of development. So, in plants, seeds, above-ground and underground parts with dormant buds overwinter. At different stages of development, winter dormancy occurs in insects (the malarial mosquito, the urticaria butterfly overwinters in the adult insect stage, the cabbage butterfly in the pupal stage, the silkworm in the egg stage).

The overwintering stages of plants and animals have many similar physiological features. The metabolic rate is significantly reduced. In birds and mammals, a state of complete suspended animation does not occur. They have developed other adaptations for winter. For example, when mammals molt, their summer coat is replaced by a thicker and longer coat with abundant undercoat, while in birds fluff is formed. This reduces heat transfer.

However, winter activity is possible only for those animals and birds that can feed themselves during this period.

Animals for which there is not enough food in winter hibernate (bats, many rodents, badgers, bears).

Birds developed seasonal migrations (flights).

The main factor in the regulation of seasonal cycles is the change in day length. The body's response to daylight hours - photoperiodism . Photoperiodism is a general, important adaptation that regulates seasonal phenomena in a wide variety of organisms.

Day length is a signaling factor that determines the direction of biological processes. The change in day length is always closely related to the temperature and precedes its change. During the year, the length of the day changes strictly regularly and is not subject to random fluctuations, like other environmental factors. Therefore, day length serves as an accurate astronomical harbinger of seasonal changes in temperature and other conditions.