Competition Among Cladocerans: Nature of the Interaction Between Bosmina and Daphnia

Abstract

Because phytoplankton succession involves pulses of short duration and a degree of unpredictability, most workers have argued against resource specialization by zooplankters. Yet, in Lake Mitchell, Vermont, two genera of cladocerans (Bosmina and Daphnia) coexist under nearly equilibrium conditions that involve an intriguing conflict. Daphnia can depress Bosmina, but apparently cannot exclude it, even though both share substantial portions of available resources. This coexistence appears mediated by the specialized foraging mode of Bosmina, which deviates markedly from filter feeding in a way that permits efficiency removal of highly edible flagellates, particularly when these items occur at low density. Evaluation of the flagellate—Bosmina association and its relationship to Bosmina—Daphnia interactions involved: (1) analysis of population responses in large—scale enclosures, (2) in situ grazing experiments with natural and introduced resources resources, and (3) laboratory preference tests. See full-text...