Tolerance

Definition

In organismal biology, the physiological or ecological capacity to survive, function, or persist under suboptimal or stressful conditions that would harm or kill less tolerant individuals or species. Tolerance describes a range, not an absolute threshold; it may be narrow (stenotolerance) or broad (eurytolerance) and can involve acclimation, genetic adaptation, or phenotypic plasticity. In ecological contexts, the term often denotes the zone of environmental conditions (temperature, humidity, salinity, desiccation, toxins) within which a population maintains positive growth. In immunological and medical entomology, tolerance may also refer to reduced pathogenicity of a parasite or reduced host inflammatory response.

Etymology

From Latin tolerare, to endure or sustain.

Example

The chironomid midge Belgica antarctica exhibits remarkable freeze tolerance, surviving intracellular ice formation and temperatures below −15°C, whereas temperate chironomids typically perish at −5°C, demonstrating how tolerance limits track evolutionary history and habitat extremes.

Synonyms

• toleration
• resistance (partial, context-dependent)
• hardiness

Related Terms

• resistance
• acclimation
• phenotypic plasticity
• stress physiology
• stenobiontic
• eurybiontic
• thermal tolerance
• desiccation tolerance
• lethal temperature
• fundamental niche

Usage Notes

Distinguish carefully from resistance: tolerance allows survival despite damage or reduced fitness, whereas resistance prevents or minimizes the stressor's effect. In vector biology, 'insecticide tolerance' implies survival at field doses without necessarily implying heritable resistance mechanisms. Tolerance is often quantified as LD50, LT50, or performance metrics across a gradient, not as a single point. The term is sometimes used loosely for behavioral avoidance; specialists reserve it for physiological or demographic capacity.