Planktivory in a Littoral-Dwelling Lake Fish Association: Prey Selection and Seasonality

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Abstract
A littoral zone assemblage of six planktivorous fishes (Pimephales notatus, Notropis heterodon, Fundulus diaphanus, Lepomis macrochirus, Ambloplites rupestris, Perca flavescens), and five zooplankter species, was analysed relative to three hypotheses concerning prey consumption: (1) Size-dependent predation will operate, as elsewhere. (2) Small-bodied planktivores, unable to handle larger prey, will take the most abundant zooplankter and not show species specialization. (3) The strongly cyclical nature of zooplankton populations will not permit fish species to specialize exclusively on zooplankton; there will be a negative correlation between zooplankton numbers and use of alternative prey, and at this time the planktivores will minimize competition by choosing different alternative prey. The first hypothesis was supported, the second and third partially so. The small specialist planktivores, P. notatus and N. heterodon, did not take the commonest small zooplankter, Bosmina longirostris: rather, they specialized largely on Chydorus sphaericus, feeding on it even when rare. Lepomis macrochirus, a generalise took largely B. longirostris, No species was exclusively planktivorous. The species only partly differed in alternative prey types eaten. Chironomid larvae were a regular item of diet of most species.