To explain the effect of different limiting factors on living organisms, number of laws and principles has been proposed by different scientists and are as follows:
1. Liebig’s Law of Minimum:
An organism requires minimum quantity of a particular nutrient for its proper growth and if it is depicted below the critical minimum level, the organism will fail to grow or will grow abnormally.
For example, if the soil is deficient in any one nutrient, it will make the other nutrient metabolically inactive and the proper growth of the plant will get restricted.
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2. Blackman’s Law of Limiting Factor:
A biological process is controlled by a number of factors and the deficiency of any of these factors will affect the process on the whole.
For example, photosynthesis by plants. Photosynthesis is dependent on right amount of water, carbon dioxide, chlorophyll, intensity of solar radiation and temperature of chloroplast. A deficiency of any of these factors will affect the rate of photosynthesis.
3. Shelford’s Law of Tolerance:
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The law states that, it is not only that the minimum amount of a material can be a limiting factor, but also the excess amount of the same material can be limiting to the growth and development of an organism.
For example, all the soil nutrients are equally important for the growth and development of plants, but anything in excess might limit the uptake of the other nutrient, restricting the proper growth.
Every organism thus, has an ecological minimum and maximum for every factor and the range between two limits is known as limit or zone of tolerance. Thus, every environmental factor has two zones: (a) Zone of tolerance (b) Zone of intolerance
(a) Zone of tolerance:
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This zone is favourable for the growth and development of organism. Zone of tolerance can be sub-divided into the following:
(i) Optimum zones:
It is the most favourable zone for growth and development of an organism.
(ii) Critical minimum zone:
It is the lowest minimum limit below which growth and development of the organism ceases.
(iii) Critical maximum zone:
It is the highest maximum limit above which growth and development of the organism ceases.
(b) Zone of intolerance:
Tolerance with respect to various factors differs from species to species. Organisms that have a wide range of tolerance for all factors have a better chance of survival and hence, are widely distributed.