Apparent exclusion of the Cladoceran Bosmina longirostris by invertebrate predator Chaoborus americanus

Zooplankton communities were sampled in 22 lakes in the Upper Peninsula of Michigan. The cladoceran Bosmina longirostris was present in 16 of 17 lakes with fish, but absent from the five without fish. The phantom midge larva species Chaoborus americanus was present only in the fishless lakes. In situ competition and pr?dation experiments were conducted in a fishless lake, Tender Bog, in which Daphnia pulex, Diaptomus leptopus and C. americanus larvae were the dominant zooplankters. Bosmina grew well alone and when reared with Daphnia, but suffered significantly greater pr?dation by Chaoborus larvae when offered as prey together with the other two species. From 8-12 months elapsed before Bosmina colonized a lake from which it had been absent. The absence of Bosmina from fishless lakes with the Tender Bog zooplankton community appears to be due not to local environmental conditions, or interspecific competition, but rather to low immigration rates and intense predation by Chaoborus larvae. Introduction