Ecology: Biology of Interaction. 5.07. Shelford’s Principle of Tolerance
Shelford’s principle can be stated as follows: among values of any condition there is a tolerance range within which the studied organism can exist. The limiting condition is the one whose value deviates most strongly from the optimum.
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5.06. Liebig’s law of the minimum
D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction Chapter 5. Autecology and Foundations of Environmental Science
5.08. Terms describing organism tolerance
5.07. Shelford’s principle of tolerance Which resource is limiting is determined by Liebig’s law of the minimum. However, not only resources can be limiting; conditions can be limiting too. What rules govern their action? In 1913, American ecologist Victor Shelford proposed the principle of ecological tolerance (endurance). According to this rule, for each factor there is a range of ecological tolerance bounded by lower and upper cardinal (critical) points, within which zones of suppression and well-being can be distinguished. Thus both low and high condition values may be unfavorable (and limiting). Therefore organism response is zero both at excessively low and excessively high values of an important condition (Fig. 5.7.1). [IMG_1] Fig. 5.7.1. Organism response to ecological factor value (condition): illustration of Shelford’s tolerance rule Shelford’s principle can be expressed as follows. Among values of any condition there is a certain tolerance range — the interval within which the studied organism can exist. The optimal condition value lies inside this range. The farther a condition value deviates from optimum, the stronger its adverse effect on the organism. Limiting among significant conditions is the one whose value deviates most strongly from optimal. Liebig’s law and Shelford’s principle can be considered parts of the limiting-factor rule. F. Clements and V. Shelford in 1939 proposed the primary-cycle concept (as many basic cycles occur, e.g., cell divisions, as permitted by full resource complex and other factors). A. Thienemann in 1942 proposed the weakest-link rule (“an organism is no stronger than the weakest link in the chain of its life requirements”). One should remember these generalizations do not account for many phenomena influencing which factor becomes limiting, including probabilistic nature of many interactions, biological compensation, complex inter-factor relationships, and actions of population and ecosystem regulatory mechanisms. Additional materials: Learning model: Ecological factors Column: Average, incomprehensible doses 5.06. Liebig’s law of the minimum
D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction Chapter 5. Autecology and Foundations of Environmental Science
D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction, Chapter 5. Autecology and Fundamentals of Environmental Science
5.08. Terms describing organism tolerance