environmental factors. limiting factor. What are the main limiting factors What is the limiting factor?

Lecture 5. Limiting factors

Different environmental factors have different significance for living organisms.

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

Limiting (limiting) factors - this is

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

In the presence of optimal combinations of many factors, one limiting factor can lead to inhibition 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, illumination, and so on. Limiting factors are indispensable 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.

Usually 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 non-eroded rocks, erosion basis, valley sides, etc.

So, the factor limiting the distribution of deer is the depth of the snow cover; butterflies of the winter scoop (a pest of vegetables and grain crops) - winter temperature, etc.

The concept of limiting factors is based on two laws of ecology: the law of the minimum and the law of tolerance.
In the middle of the 19th century, the German organic chemist Liebig, studying the effect of various trace elements on plant growth, was the first to establish the following: plant growth is limited to an element whose concentration and value is at a minimum, that is, it is present in a minimal amount. Figuratively, the law of the minimum helps to represent the so-called Liebig barrel.

This is a barrel with wooden slats of different heights, as shown in the picture. It is clear that no matter how high the other slats are, you can pour water into the barrel exactly as much as the height of the shortest slat. So the limiting factor limits the vital activity of organisms, despite the level (dose) of other factors. For example, if yeast
placed in cold water, low temperature will become a limiting factor in their reproduction. Every housewife knows this, and therefore leaves the yeast to “swell” (and actually multiply) in warm water with a sufficient amount of sugar. It remains only to “change” some terms: let the height of the poured water be some kind of biological or ecological function (for example, productivity), and the height of the rails will indicate the degree of deviation of the dose of one or another factor from the optimum.

At present Liebig's law of the minimum is interpreted more widely. A limiting factor can be a factor that is not only in short supply, but also in excess.

The environmental factor plays the role of a LIMITING FACTOR if this factor is below the critical level or exceeds the maximum tolerable level.

The limiting factor determines the distribution area of the species or (under less severe conditions) affects the general level of metabolism. For example, the content of phosphates in sea water is a limiting factor that determines the development of plankton and the overall productivity of communities.

The concept of "limiting factor" applies not only to various elements, but to all environmental factors. Competitive relations often act as a limiting factor.

Each organism has its own limits of endurance in relation to various environmental factors. Depending on how wide or narrow these limits are, eurybiont and stenobiont organisms are distinguished. eurybionts able to endure a wide range of intensity of various environmental factors. For example, the habitat of a fox is from the forest-tundra to the steppes. Stenobionts, on the contrary, tolerate only very narrow fluctuations in the intensity of the environmental factor. For example, almost all tropical rainforest plants are stenobionts.

Law of Tolerance

The concept that, along with the minimum, the 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 ecological factors, the values of which 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 both a minimum and 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)"

The favorable range of the environmental factor is called the zone of optimum (normal life). The greater the deviation of the factor from the optimum, the more this factor inhibits the vital activity of the population. This range is called the zone of oppression or pessimism. The maximum and minimum tolerated values of the 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 complete existence of the population. Individuals may have slightly different tolerance ranges.

Environmental factors always act on organisms in a complex. Moreover, the result is not the sum of the impact of several factors, but is a complex process of their interaction. At the same time, the viability of the organism changes, specific adaptive properties arise that allow it to survive in certain conditions, to endure fluctuations in the values of various factors.

The influence of environmental factors on the body can be represented in the form of a diagram (Fig. 94).

The most favorable intensity of the environmental factor for the organism is called optimal or optimum.

Deviation from the optimal effect of the factor leads to inhibition of the vital activity of the organism.

The boundary beyond which an organism cannot exist is called endurance limit.

These boundaries are different for different species and even for different individuals of the same species. For example, the upper atmosphere, thermal springs, and the icy desert of Antarctica are beyond the limits of endurance for many organisms.

An environmental factor that goes beyond the limits of an organism's endurance is called limiting.

It has upper and lower limits. So, for fish, the limiting factor is water. Outside the aquatic environment, their life is impossible. A drop in water temperature below 0 °C is the lower limit, and an increase above 45 °C is the upper limit of endurance.

Rice. 94. Scheme of the action of the environmental factor on the body

Thus, the optimum reflects the characteristics of the habitat conditions of various species. In accordance with the level of the most favorable factors, organisms are divided into heat- and cold-loving, moisture-loving and drought-resistant, light-loving and shade-tolerant, adapted to life in salt and fresh water, etc. The wider the endurance limit, the more plastic the organism. Moreover, the limit of endurance in relation to various environmental factors in organisms is not the same. For example, moisture-loving plants can tolerate large temperature fluctuations, while the lack of moisture is detrimental to them. Narrowly adapted species are less plastic and have a small endurance limit, while widely adapted species are more plastic and have a wide range of fluctuations in environmental factors.

For fish living in the cold seas of Antarctica and the Arctic Ocean, the range of tolerable temperatures is 4–8 °C. As the temperature rises (above 10 °C), they stop moving and fall into thermal stupor. On the other hand, fish of equatorial and temperate latitudes endure temperature fluctuations from 10 to 40 °C. Warm-blooded animals have a wider range of endurance. Thus, Arctic foxes in the tundra can tolerate temperature fluctuations from -50 to 30 °C.

Plants of temperate latitudes withstand temperature fluctuations in the range of 60-80 ° C, while in tropical plants the temperature range is much narrower: 30-40 ° C.

Interaction of environmental factors lies in the fact that a change in the intensity of one of them can narrow the endurance limit to another factor or, conversely, increase it. For example, optimal temperature increases tolerance to lack of moisture and food. High humidity significantly reduces the body's resistance to high temperatures. The intensity of the impact of environmental factors is directly dependent on the duration of this impact. Prolonged exposure to high or low temperatures is detrimental to many plants, while plants tolerate short-term drops normally. The limiting factors for plants are the composition of the soil, the presence of nitrogen and other nutrients in it. So, clover grows better on soils poor in nitrogen, and nettle - on the contrary. A decrease in the nitrogen content in the soil leads to a decrease in the drought resistance of cereals. On salty soils, plants grow worse, many species do not take root at all. Thus, the adaptability of the organism to individual environmental factors is individual and can have both a wide and a narrow range of endurance. But if the quantitative change of at least one of the factors goes beyond the limit of endurance, then, despite the fact that other conditions are favorable, the organism dies.

The set of environmental factors (abiotic and biotic) that are necessary for the existence of a species are called ecological niche.

The ecological niche characterizes the way of life of the organism, the conditions of its habitat and nutrition. In contrast to a niche, the concept of habitat refers to the territory where an organism lives, i.e. its “address”. For example, herbivorous inhabitants of the steppes cow and kangaroo occupy the same ecological niche, but have different habitats. On the contrary, the inhabitants of the forest - squirrel and elk, also related to herbivores, occupy different ecological niches. The ecological niche always determines the distribution of the organism and its role in the community.

LIMITING

The influence of environmental factors on living organisms is diverse, but at the same time, general patterns of their action can be distinguished. With an extremely weak or extremely strong influence of the factor, the vital activity of organisms undergoing these influences is suppressed. The factor acts most favorably at values that are optimal for a given organism. The range of action of the ecological factor, in which the existence of this species is possible, is area of tolerance kind. The area of tolerance is limited by the points of minimum and maximum, they correspond to the extreme values of this factor, at which the existence of organisms is possible. The value of the factor that corresponds to the best indicators for the life of a particular species is called optimal, or optimum point(Fig. 3). Points of optimum, minimum and maximum determine the "reaction rate" of the organism to this factor. The extreme points of the curve, which express the state of oppression of organisms with a lack or excess of environmental factors, are called areas of pessimum. Beyond these points, i.e. outside the tolerance zone, the value of the environmental factor is lethal (fatal) for living organisms.

Fig.3. The influence of changes in the quantitative expression of the environmental factor on the vital activity of the organism (it is assumed that all other factors act at the optimum). 1 - the degree of favorability of these doses for the body: 2 - the amount of costs required for adaptation

Environmental conditions under which any factor or their combination have a depressing effect on the vital activity of organisms are called limiting. Environmental factors that, under specific environmental conditions, have values that are farthest from optimal, make it difficult for the species to exist in these conditions, despite the optimal values of other factors. Such factors are called limiting factors. Limiting factors become of paramount importance for the life of the species, and ultimately determine the boundaries of the habitat of this species, its geographic range.

Optimal - the most favorable intensity of the environmental factor for the body - light, temperature, air, soil, humidity, food, etc.

Limiting factors 1) any factors that inhibit the growth of a population in an ecosystem; 2) environmental factors, the value of which strongly deviates from the optimum.
In the presence of optimal combinations of many factors, one limiting factor can lead to inhibition 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, illumination, and so on. Limiting factors are indispensable 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 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

Considering the theory of minima, one should not confuse the leading and limiting factors of the environment, since the latter can be both main and secondary. The limiting condition is usually the condition that has deviated the most from the norm. If indicators are beyond the limits of stability, regardless of whether they have changed towards a minimum or towards a maximum, they turn into limiting factors. This also takes place when all other conditions are favorable or optimal.

Shelford Limiting Factors

The theory discussed above was developed after 70 years. The American scientist Shelford found that not only an element present in a minimum concentration can affect the development of an organism, but its excess can also cause adverse effects. For example, both excessive and insufficient water will be harmful for a plant. In the latter case, acidification of the soil will occur, and in the first case, the assimilation of nutrient compounds will be difficult. Many organisms are adversely affected by changes in pH and other limiting factors. Tolerance, within which a normal existence is possible, is limited, in fact, by a lack or excess of conditions, the indicators of which can be close to the limits of tolerance.

Endurance range

The limits of tolerance are not constant. For example, the range can narrow if any condition approaches one or another boundary. This situation also occurs during the reproduction of organisms, when many indicators become limiting. From this it follows that the influence of many limiting environmental factors is variable. This means that one condition may or may not be oppressive or restrictive.

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 manifests itself most effectively at the community level. With such compensation, conditions are formed for the physiological adaptation of the species - the eurybiote, which is widespread. Acclimatizing in a certain territory, it forms a kind of ecotype, a population, the limits of tolerance of which correspond to the locality. Deeper adaptation processes can contribute to the formation of genetic races.

Implementation of theory in practice

To have the clearest idea of how limiting environmental factors affect organisms, we can take the development of plants under the influence of carbon dioxide as an example. Its content in the air is small, so even a slight fluctuation in its level will be of great importance for plantations. 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 in time. So, in winter and autumn, the concentration of carbon dioxide is increased due to differences in the photosynthetic activity of green spaces. At the same time, 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 negatively affect their development and growth, appearance, internal processes. A typical CO2 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 due to the activity of heterotrophs, the reproduction of which 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 features of light-loving plantations predominate in the plant. In particular, they differ:

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

Along with this, dandelions that grow in the shade have the following traits:

Underdeveloped root system.
Large, wide, thin leaves with sparse venation, located perpendicular to the rays, etc.

When analyzing sections of leaf blades of the first and second species of dandelion, one can also find deeper histological differences that complement the morphological features discussed above. The influence of temperature fluctuations is also quite clearly manifested. At the same time, if the transformation with a change 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 indented leaves form on plants. If, in this form, a dandelion is transferred to a greenhouse, where t is +15 ... + 18 degrees, plates with solid edges will begin to develop. When the plant is placed in intermediate conditions, the leaves will have a slight indentation.

Chain reaction

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

Introduction

In this paper, I will cover the topic "Limiting Factors" in detail. I will consider their definition, types, laws and examples.

Different environmental factors have different significance for living organisms.

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

Main part

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

Limiting (limiting) factors - this is

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

Limiting factors for terrestrial ecosystems:

Temperature;

Nutrients in the soil.

Limiting factors for aquatic ecosystems:

Temperature;

Sunlight;

Salinity.

Examples of limiting factors are: outcrops of non-eroded rocks, erosion basis, valley sides, etc.

So, the factor limiting the distribution of deer is the depth of the snow cover; butterflies of the winter scoop (a pest of vegetables and grain crops) - winter temperature, etc.

The concept 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 middle of the 19th century, the German organic chemist Liebig, studying the effect of various trace elements on plant growth, was the first to establish the following: plant growth is limited to an element whose concentration and value is at a minimum, that is, it is present in a minimal amount. Figuratively, the law of the minimum helps to represent the so-called Liebig barrel. This is a barrel, wooden slats have different heights, as shown in the picture

. It is clear that no matter how high the other slats are, you can pour water into the barrel exactly as much as the height of the shortest slat. So the limiting factor limits the vital 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 in 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, and light, and water, and oxygen, and other factors can limit or limit the development of organisms, if their rolling corresponds to the ecological minimum. For example, tropical fish angelfish die 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 value under specific conditions, especially limit the possibility of the existence of a species in these conditions, despite and despite optimal combination of other hotel conditions.

In its modern formulation, the law of the minimum reads as follows: the endurance of an organism is determined by the weakest link in the chain of its ecological needs .

For the successful application of the law of limiting factors in practice, two principles must be observed:

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

The second one 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 close one. So, in places where there is a lot of strontium, in mollusk shells, it can replace calcium with a lack 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 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 the minimum, the 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, the values of which 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 both a minimum and 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 the environmental factor on its intensity

The favorable range of the environmental factor is called optimum zone (normal activity). The greater the deviation of the factor 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 tolerated values of the 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 complete existence of the population. Individuals may have slightly different tolerance ranges.

Later, tolerance limits were established for various environmental factors 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 able to change 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 climb into warm water, and then gradually add hot water. This adaptation to the slow change of the factor is a useful protective property. But it can also be dangerous. Unexpected, without warning signals, even a small change can be critical. There comes a threshold effect: the last straw "can be fatal. For example, a thin twig can break a camel's already overstretched back.

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, weeds often become a limiting factor, and for some plants, a lack (or absence) of representatives of another species becomes a limiting factor in development. In accordance with the law of tolerance, any excess of matter or energy turns out to be a source of pollution. Thus, excess water even in arid regions is harmful, and water can be considered as a common pollutant, although it is simply necessary in optimal quantities. In particular, excess water prevents normal soil formation in the chernozem zone.