Shelford's Law of Tolerance was formulated in 1913. It was he who became the most important law in ecology. Consider its essence in more detail, give specific examples.
Wording and Terms
Currently, the following interpretation is used: the existence of an ecosystem or ecological species is characterized by limiting factors that are both at a minimum and a maximum.
Tolerance is the ability of an organism or ecosystem to tolerate the adverse effects of some environmental factor.
Shelford's law of tolerance significantly expands the possibilities of the law of minimum formulated by Liebig.
Features
The revolution of the law in question is that not only the insignificant effect of a single factor (food, light, water) negatively affects the body. Shelford was able to prove that the excess of the influence of a single factor is also harmful. He managed to find out that in the ecological system an organism can exist only within the limits of tolerance - from minimum to maximum.
If the factor takes an indicator below the minimum, then the body is threatened with death (Liebig's law). The law of tolerance makes it clear that at maximum rates it also perishes.
First example
Consider the living conditions of crocodiles. For a normal existence, they need water. Its absence or reduction in volume leads to death. Excess water will also negatively affect the existence of crocodiles.
What is the essence of the law of tolerance in this example? Equally negative harm is caused by both a shortage and an excess of water. Consequently, crocodiles will not survive either in the desert or in the oceans.
The broad scope of the law
We will analyze tolerance using the example of the number of training an athlete. If the athlete will train occasionally, it will be difficult for him to count on victory in the Olympic Games. With excessive training, he will get tired even before the start of the competition, which will not give him the opportunity to take a prize.
This example demonstrates that the law of tolerance in ecology has a wide scope. In this case, it goes beyond the boundaries of classical science.
Additional Information
According to the law of tolerance, the ecological law of optimum was derived. It also allows you to formulate several additional principles:
organisms may have a wide range of tolerance for a particular factor and a narrow range for another;
organisms with a wide range of tolerance to various factors are more widespread;
if, for one factor, the conditions are not optimal for the species, the range of tolerance to other environmental factors also narrows significantly.
For example, the limiting nitrogen content leads to a decrease in drought tolerance of cereals. In other words, it was found that insufficient nitrogen should be accompanied by an increase in water intake.
In living nature, organisms quite often find themselves in conditions that do not correspond to the ideal range of any physical factor that was identified in a research laboratory. In such situations, another factor or their combination becomes the most important.
For example, when cooled, the growth of tropical orchids increases. In nature, they develop only in the shade, plants are not able to tolerate the thermal effects of direct sunlight.
The law of tolerance was formulated by Shelford, therefore it is he who is considered the founder of this theory.
Due to the inter-population and interpopulation relationships, problems arise using the optimal environmental conditions of organisms. For example, it can be parasites, predators, competitors.
Interesting Facts
Very often the breeding season is critical. It was at this time that many environmental factors became limiting. This is the basis of tolerance. The law of tolerance clarifies the limits for seeds, individuals, eggs, sprouts, embryos, larvae.
Adult cypress is able to multiply and grow, being constantly immersed in water, on a dry plateau, and it can reproduce only if there is only slightly moist soil.
Where else is tolerance manifested? The law of tolerance can be considered on the example of blue crabs. They, like other sea animals, carry fresh and sea water, so they can be seen in rivers. The crab larvae are not able to survive in such waters, therefore, their reproduction in rivers is not observed, this is tolerance. The law of tolerance explains the geographical distribution of commercial fish, the relationship of this factor with the climate.
Classification of organisms by environmental valency
Endurance limits between critical points are called the environmental valency of living things, depending on the specific environmental factor. Representatives of various species differ significantly from each other both in ecological valency and in the optimum position. For example, in the tundra, Arctic foxes can tolerate temperature fluctuations in the range of more than 80 degrees.
Warm-water crustaceans can withstand water temperatures only in the range of about 6 degrees. The same power of factor manifestation is able for one species to be optimal, and for another to go beyond endurance.
To indicate the wide ecological valency of a species in relation to abiotic environmental factors, it is customary to use the prefix “evry”.
Heuristic species can tolerate significant temperature fluctuations, and eurybate species cope with a wide pressure range. There are euryhaline organisms for which the degree of salinization of the environment is not terrible.
A narrow ecological valency is considered the inability of organisms to tolerate large differences of certain factors. In this case, the prefix "wall" is used: stenohaline, stenobatny, stenothermal.
In a broader sense, it implies compliance with certain environmental conditions, called stenobiont, under which adaptation to various environmental conditions is possible.
To summarize
What does tolerance matter? The law of tolerance connects both maxima and minima of various factors. He explains the stamina of organisms in relation to specific conditions. In the XX century, the American scientist Shelford was able to show that with an excess or deficiency of a certain condition (temperature, pressure, salinity), the vital activity of the body changes significantly.
Depending on the ability to adapt to the environment, it is customary to distinguish:
The second group includes plants and animals that can fully exist and develop only in constant environmental conditions (humidity, temperature, food). This group includes internal parasites. Part of stenobionts is characterized by dependence only on a specific factor.
For example, the life of a marsupial koala bear is affected only by the presence of eucalyptus, whose leaves are its main food.
Eurybionts are organisms that can tolerate significant changes in environmental conditions. An example of them can be considered starfish that live in the tidal range. They are ways to tolerate dehumidification during low tide, heating in the summer, cooling in the winter.
An important consequence of hierarchical organization is the fact that when combining components or subsets into large units, they acquire new properties that were previously absent. New qualities that have appeared cannot be predicted, predicted, or explained their specific features. Thanks to the law of tolerance, it became possible to explain and predict many phenomena occurring in living nature.