Not to be confused with Paradox of tolerance.
Shelford's law of tolerance is a principle developed by American zoologist Victor Ernest Shelford in 1911. It states that an organism's success is based on a complex set of conditions and that each organism has a certain minimum, maximum, and optimum environmental factor or combination of factors that determine success. The further elaboration on the theory of tolerance is credited to Ronald Good.
- Points out the second limitation of Liebig's law of the minimum - that factors act in concert rather than in isolation. A low level of one factor can sometimes be partially compensated for by appropriate levels of other factors.
In case of chemical reactions it is known as law of limiting factor.
- A corollary to this is that two factors may work synergistically (e.g. 1 + 1 = 5), to make a habitat favorable or unfavorable.
- Geographic distribution of sugar maple.
- It cannot tolerate average monthly high temperatures above 24–27 °C or winter temperatures below −18 °C. The western limit is determined by dryness, and this coincides with the western limits of forest vegetation in general.
- Because temperature and rainfall interact to determine the availability of water, sugar maple tolerates lower annual precipitation at the edge of its northern range (by about 50 cm).
- Good restated the theory of tolerance as: Each and every species is able to exist and reproduce successfully only within a definite range of environmental conditions.
- The law of tolerance, or theory of tolerance, is best illustrated by a bell shaped curve.
- The range of the optimum.
- Tolerance ranges are not necessarily fixed. They can change as:
- Seasons change.
- Environmental conditions change.
- Life stage of the organism changes.
- Example – blue crabs. The eggs and larvae require higher salinity than adults.
- The range of the optimum may differ for different processes within the same organism.
- Photosynthesis and growth in the pea plant
References
- Shelford, V. E. (July 1, 1931). "Some Concepts of Bioecology". Ecology. 12 (3): 455–467. doi:10.2307/1928991. ISSN 1939-9170. JSTOR 1928991.
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