Variable life history of a cyclopoid copepod: The role of food availability

Populations of the copepod Cyclops vicinus in two Danish lakes differed in their life cycles. In Lake Vaeng C, vicinus was absent during summer, whereas in Lake Sobygard it continued producing distinct cohorts throughout summer. A comparison between the lakes showed that in the lake where C. vicinus was absent during summer, food limitation generally existed. In contrast, abundance of C. vicinus during summer in Lake Sobygard always coincided with available resources sufficient for the whole lifecycle. Thus, summer diapause of C. vicinus is suggested to be a strategy to avoid food limitation. Avoidance of fish predation does not seem substantially to influence life cycles.