Shelford\'s law of tolerance PDF

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Lecture notes by Dr. Sabiha Khanam of Aligarh Muslim University....

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Some further examples of limiting factors: Oxygen in a billabong (River Canal) • Water in a desert • Light in the ocean depths • Nutrients in the upper layers of the Sea

Shelford's law of tolerance Shelford's law of tolerance A law proposed in 1911 by V. E. Shelford, stating that the presence and success of an organism depend upon the extent to which a complex of conditions is satisfied (e.g. the climatic, topographic, and biological requirements of plants and animals). The absence or failure of an organism can be controlled by the qualitative or quantitative deficiency or excess of any one of several factors which may approach the limits of tolerance for that organism. Organisms have an ecological maximum and minimum, with a range in between which represents the “limits of tolerance”.

Every population thrives in an optimal range of abiotic factors. • Beyond this range, one finds less and less numbers of these organisms. • In an ecosystem, it is harder to represent what this optimal range is, since a host of factors affect the survivability of this population. • Often, the range is shown for each factor, and this is known as the range of tolerance.

Combined concept of limiting factors A more complex expression of the ecological conditions determining the dispersal and growth of organisms is obtained in combination of Liebig-Blackman law of the minimum with Shelford’s law of limit of tolerance. According to Odum, the presence and success of an organism and group of organisms depends upon a complex of conditions. Any condition that exceeds the limit of tolerance is said to be limiting factor. Among others, the temperature is quite often a limiting factor. Thus, organisms are controlled in nature by •

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the quantity and variability of material for which there is a minimum requirement and physical factors which are critical and the limits of tolerance of organisms themselves to these and other components of the environment. The combined concept helps in understanding the complex environmental relationship in nature....