The German scientist Justut Liebig found that the productivity of cultivated plants primarily depends on the nutrient or mineral element that is present in the soil in the smallest amount.
Liebig’s Law of Minimum (or Law of Limiting Factors):
the successful vital activity of the organism is limited by the ecological factor, the quantity and quality of which are close to the minimum required by the organism.
The figurative representation of the law of minimum is the so-called Liebig’s barrel.
The essence of the model is that when the barrel is filled, water begins to overflow over the smallest board in the barrel, and the length of the remaining boards no longer matters.
Example: if phosphorus in the soil is only 20% of the required norm, and calcium is 50% of the norm, then the plant will develop only until it has absorbed all the phosphorus. Low phosphorus content will be a limiting factor for further growth. To increase productivity, it is first of all necessary to apply a phosphorus-containing fertilizer to the soil.
But an excess of any environmental factor can have the same negative impact on the development of the body as its deficiency.
Factors that prevent the normal development of a living organism due to their excess or deficiency in comparison with the needs are called limiting.
Shelford’s law of tolerance: the limiting factor limiting the development of the organism can be at least and maximum impact of the environmental factor.
Tolerance (from Lat. Tolerantia – “patience”) – the ability of organisms to withstand changes in living conditions (for example, fluctuations in temperature, humidity, light). This property of living organisms is very important, it allows you to adapt to constantly changing conditions. In different species, tolerance towards certain factors is expressed to varying degrees.
Example: For a plant, both lack and excess of moisture in the soil can be detrimental.
Optimum law: any environmental factor has certain limits of positive influence on living organisms.
Graphically, the law of the optimum is expressed by a symmetric dome-shaped curve (tolerance curve), showing how the vital activity of the species changes with a gradual increase in the influence of the factor.
The limits of endurance (ecological valence) are the minimum and maximum values of the factor at which vital activity is possible. The boundaries beyond which the death of organisms occurs are the lower and upper limits of the endurance of the species. These are called tipping points.
Example: animals and plants do not tolerate extreme heat and severe frosts; average temperatures are optimal. Likewise, drought and constant heavy rains are equally unfavorable for the crop.
The highest indices of vital activity are observed at the optimal values of the factor for the organisms of the studied species.
All organisms in the course of evolution have developed the ability to adapt to one or another range of factors. In some species, the limits of endurance for a certain factor are narrow. This means that they can only exist under relatively constant environmental conditions. In this case, narrow curves are obtained.
Gentle curves are observed if the limits of endurance of the species for this factor are wide. Species with a wide range of tolerance have more opportunities for distribution in the environment.
But for different factors, the limits of endurance are different: for one factor, a species can have wide limits, and for others, narrow ones.
The law of relative independence of adaptation of organisms: the degree of endurance to any factor does not mean the corresponding ecological valence of the species in relation to other factors.
Species that tolerate wide temperature changes do not necessarily have to adapt to wide fluctuations in humidity or salt regime either.
Example: Many amphibians can withstand significant temperature fluctuations, but cannot tolerate even short-term drying of the skin.
The law of joint action of factors: the result of the influence of any environmental factor depends primarily on the combination and with what force other factors act.
It is much easier to endure frost in calm weather than in strong wind. The body tolerates heat much worse at high humidity.
The law of irreplaceability of a factor: one cannot completely replace one factor with another.
Example: The light needed by plants for photosynthesis cannot be replaced by excess heat or carbon dioxide.