Liebig's law of minimum.V. Shelford's law of tolerance

Despite a wide variety of environmental factors, there are a number of common things in the character of their impact on organisms and in response of living beings.

The law of optimum. Each factor has its limits of positive effect on organisms (Figure 1). The result of the variable factor depends primarily on the strength of its manifestation. Both insufficient, and redundant impact of the factor negatively affects the vital activity of living organisms. The favorable impact is called a zone of optimum of the environmental factor or simply an optimum for organisms of the given species. The greater the deviation from the optimum is, the more negatively this factor effects organisms (zone of pessimum). Maximum and minimum values ​​of the factor - are critical points beyond which the existence is no longer possible, and death occurs. Conditions when one or several factors come close to critical points are called extreme. Limits of endurance between the critical points are called ecological valence of living organisms in relation to a particular environmental factor. Ecological valence - is a property of species to adapt to a particular range of environmental factors.

Wide ecological valence of species with respect to environmental factors is marked by a prefix of ''eury' to the factor.  Eurythermic species - enduring large fluctuations in temperature, eurybathic - enduring wide range of pressure, euryhaline - enduring different salinity levels of the environment.

Inability to endure large fluctuations of the factor, or narrow ecological valence, is characterized by the prefix "steno" - stenothermal, stenobathic, stenohaline types, etc.

Species, the existence of which is strictly conditioned by certain environmental conditions, are called stenobiontic (environmentally non-plastic, highly specialized, not endurable), and those that are able to adapt to different environmental conditions - eurybiontic (more endurable, highly specialized).

"Growth and development of organisms depend primarily on those environmental factors, the value of which is close to the ecological minimum" - Liebig's law of minimum (1873). It follows from the law that:

a) endurance of organisms is determined by the weakest link in the chain of its environmental requirements;

b) all circumstances necessary to maintain life, are equal (the law of equivalence of living conditions), any factor can limit the possibility of existence of the organism.

The law of minimum is closely connected with the law of limiting factors, or F. Blekhman's law (1909): environmental factors that have maximum values in particular conditions, especially hinder (limit) species abilities to survive in these conditions. In other words, a factor which is in shortage or excess (near critical points) negatively affects organisms and also limits the manifestation of other factors, which can be at their optimum.

These laws are supplemented by V. Shelford's Law of Tolerance (1913): a limiting factor for existence of an organism can be both a minimum and maximum of the environmental impact, and the range between them determines the scope of resistance to this factor.

The greater is the deviation from the optimum, the more suppressive is this factor for the organism. Both insufficient, and redundant effect of the factor negatively affects living of organisms.

Any natural systems can develop only through the use of material, energy and information capacities of the environment. Isolated development is impossible. Development of nature is subject to certain laws.

Ecological environmental factors have various impacts on living organisms, that is, can affect as irritators causing adaptive changes in physiological and biochemical functions, as delimiters that make it impossible to exist in these conditions, as modifiers, causing morphological and anatomical changes in organisms; as signals indicating changes in other environmental factors.

Let's consider ecological importance of certain factors.

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$$$003-012-001$3.3.12.1 Методические указания к практическому занятию №12

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Questions for self-control

Into what groups can we classify the environmental factors?

What factors are called abiotic factors of the environment?

What environmental factors are biotic?

Which factor is called edaphic?

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Find in the text English equivalents of the following words and expressions. Translate the sentences which contain them.

1) эвритермные организмы; 2) стенотермные 3) закон минимума Либиха; 4) зона пессимума; 5) экологическая валентность.

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$$$003-013-000$3.3.13 Практическое занятие №13

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