Shelford's law of tolerance

Shelford's law of tolerance states that an organism's presence and success depend on environmental conditions staying within its minimum and maximum tolerance limits. Performance is often greatest near an optimum and declines toward either limit.

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Tolerance range: The interval of environmental conditions within which an organism can survive or function. The law describes how each condition has a lower and upper limit for an organism.
Ecological niche: The set of environmental conditions and resources under which a species can persist and reproduce. Tolerance limits help define the environmental dimensions of a species' niche.
Indicator species: A species whose presence, absence, or abundance provides information about environmental conditions. A species' known tolerance can make its distribution evidence of local conditions.
Victor Ernest Shelford: An American ecologist who formulated the law of tolerance and helped develop animal ecology. Shelford proposed the principle that bears his name.
Ecological optimum: The environmental condition or range at which an organism performs best. Performance generally peaks between the minimum and maximum tolerance limits.
Fundamental niche: The full range of conditions and resources under which a species can maintain a population without biotic constraints. Tolerance determines which abiotic conditions fall within this potential range.
Bioindicator: A biological measure used to assess environmental quality or change. Tolerance thresholds help explain which organisms signal pollution or other environmental stress.
Animal communities in temperate America: A 1913 book by Victor E. Shelford describing ecological communities and animal succession. Shelford's early ecological work helped establish his account of environmental tolerances.
Limiting factor: An environmental resource or condition that restricts a biological process or population. A condition near either tolerance limit can restrict an organism even when other conditions are favorable.
Population ecology: The study of how and why populations change in size, structure, and distribution. Tolerance limits influence survival and reproduction, and thus population trajectories.