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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. [ 1 ]
A tolerance interval (TI) is a statistical interval within which, with some confidence level, a specified sampled proportion of a population falls. "More specifically, a 100×p%/100×(1−α) tolerance interval provides limits within which at least a certain proportion (p) of the population falls with a given level of confidence (1−α)."
All species have limits of tolerance to abiotic factors. Too much or too little of anything can lower their survival and reproductive success and cause reduced fitness. Changes in temperature resulting from global warming, for example, may cause a species to change its geographical distribution northward.
A highly tolerant species would receive a value of 10, while a species collected only in unaltered streams with high water quality would receive a value of 0. [ 2 ] [ 3 ] The sum products of the number of individuals in each species (or genera) multiplied by the tolerance of the species is divided by the total number of specimens in the sample ...
Species distribution, or species dispersion, [1] is the manner in which a biological taxon is spatially arranged. [2] The geographic limits of a particular taxon's distribution is its range , often represented as shaded areas on a map.
The species–area relationship or species–area curve describes the relationship between the area of a habitat, or of part of a habitat, and the number of species found within that area. Larger areas tend to contain larger numbers of species, and empirically, the relative numbers seem to follow systematic mathematical relationships. [1]
The method is based on the principle that different aquatic invertebrates have different tolerances to pollutants. In the case of BMWP, this is based on the sensitivity/tolerance to organic pollution (i.e. nutrient enrichment that can affect the availability of dissolved oxygen). It is important to recognise that the ranking of sensitivity ...
The weighting factor g has a value of either 1, 2, 4, 8 or 16, and denotes a tolerance range. If a species can survive in both unpolluted and heavily polluted water, g is very small because finding the species in a survey has little predictive value. In practice, only indicator species with a weighting factor g ≥ 4 are used.