Shelford's Law of Tolerance was formulated in 1913. It was he who became the most important law in ecology. Let's take a closer look at its essence, give specific examples.
Formulations 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 at a maximum.
Tolerance is the ability of an organism or ecosystem to endure the adverse effects of some environmental factor.
Shelford's law of tolerance significantly expands the possibilities of Liebig's law of the minimum.
Features
The revolutionary nature of the law under consideration lies in the fact that not only the slight impact of a single factor (nutrition, 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 ecologicalsystem, an organism can exist only within 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 explains that even at maximum rates, it also dies.
First example
Consider the living conditions of crocodiles. They need water to survive. Its absence or decrease 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 has both a lack and an excess of water. Therefore, crocodiles will not survive in the desert or in the world's oceans.
Wide scope of the law
Tolerance will be analyzed on the example of the number of trainings of an athlete. If an athlete trains occasionally, it will be difficult for him to count on winning the Olympic Games. With excessive training, he will be tired 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, he goes beyond classical science.
Additional information
According to the law of tolerance, the ecological law of optimum was derived. It also allows the formulation of several additional principles:
- organisms can have a wide rangetolerance for a particular factor and a narrow range for another;
- organisms with a wide range of tolerances to various factors are more widespread;
- if conditions for one factor are not optimal for the species, the range of tolerance to other environmental factors is also significantly narrowed.
For example, the limiting content of nitrogen leads to a decrease in the drought tolerance of cereals. In other words, it was found that insufficient nitrogen should be accompanied by an increase in water intake.
In nature, it is not uncommon for organisms to find themselves in conditions that fall outside the ideal range of any physical factor that has been identified in a research laboratory. In such situations, another factor or a combination of them becomes the most important.
For example, cooling increases the growth of tropical orchids. 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, which is why he is considered the founder of this theory.
Because of intrapopulation and interpopulation relationships, problems arise with the use of optimal environmental conditions for the existence of organisms. For example, it can be parasites, predators, competitors.
Interesting facts
Very often the breeding season is critical. It is at this time that many become limitingenvironmental factors. This is the basis of tolerance. The law of tolerance clarifies the limits for seeds, individuals, eggs, sprouts, embryos, larvae.
An adult cypress is able to reproduce and grow while constantly submerged in water, on a dry highland, and it can only reproduce in the presence of only slightly moist soil.
Where else is tolerance manifested? The law of tolerance can be seen on the example of blue crabs. They, like other marine animals, tolerate fresh and sea water, so they can be seen in rivers. Crab larvae are not able to survive in such waters, so their reproduction in the 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 ecological valency
The limits of endurance between critical points are called the ecological valency of living beings, depending on a specific environmental factor. Representatives of different species differ significantly from each other both in ecological valence and in the position of the optimum. For example, in the tundra, Arctic foxes are able to tolerate temperature fluctuations in the range of more than 80 degrees.
Heat-water crustaceans can only withstand water temperatures in the range of about 6 degrees. The same strength of the manifestation of a factor is capable of being optimal for one species, and for another to go beyond the limits of endurance.
To designate a wide ecological valence of a species in relation toabiotic factors of the environment, it is customary to use the prefix "evry".
Eurytic species are able to tolerate significant temperature fluctuations, while eurybat species cope with a wide range of pressure. There are also euryhaline organisms for which the degree of salinity of the environment is not terrible.
Narrow ecological valency is the inability of organisms to endure large fluctuations in certain factors. In this case, the prefix "steno" is used: stenohaline, stenobat, stenoterm.
In a broader sense, it implies compliance with certain environmental conditions, called stenobiont, under which adaptation to various environmental conditions is possible.
Summarize
What is the significance of tolerance? The law of tolerance connects both the maximums and minimums of various factors. It also explains the endurance of organisms in relation to specific conditions. In the 20th century, the American scientist Shelford managed to show that with an excess or deficiency of a certain condition (temperature, pressure, salinity), the vital activity of the organism changes significantly.
Depending on the ability to adapt to the environment, it is customary to allocate:
- eurybionts (they are characterized by a wide range of environmental factors);
- stenobionts (exist in a narrow range)
The second group includes plants and animals that can fully exist and develop only in constant environmental conditions(humidity, temperature, presence of food). This group includes internal parasites. Some stenobionts are 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 endure dehumidification at low tide, heating during the summer, cooling during the winter.
An important consequence of the hierarchical organization is the fact that when components or subsets are combined into large units, they acquire new properties that were previously absent. New qualities that have appeared cannot be predicted, predicted, and their specific features cannot be explained. Thanks to the law of tolerance, it became possible to explain and predict many phenomena occurring in wildlife.
