Kinesis

Definition

A non-directional movement or change in activity rate in response to a stimulus, in which the organism does not orient toward or away from the stimulus source but instead alters its speed of movement or frequency of turning. Unlike taxis, kinesis produces a statistical distribution effect: increased movement typically leads to departure from unfavorable conditions, while decreased movement promotes retention in favorable zones. Orthokinesis involves speed modulation; klinokinesis involves turning frequency.

Etymology

Greek kinesis, motion, movement

Example

A woodlouse in a dry patch exhibits orthokinesis by increasing its walking speed until it chances upon humid microhabitat, where reduced speed promotes aggregation; similarly, a fly larva in bright light shows klinokinesis by turning frequently, increasing the probability of entering darker refuges.

Related Terms

• Taxis
• orthokinesis
• klinokinesis
• stereokinesis
• thermokinesis
• Photokinesis
• klinotaxis
• tropotaxis

Usage Notes

Distinguished from taxis by the absence of oriented movement toward or away from a stimulus gradient. Specialists reserve kinesis for cases where turning or speed changes are random with respect to stimulus direction, not directed. The term is sometimes misapplied to any movement response; precise usage requires demonstrating that orientation is absent or irrelevant to the adaptive outcome.