Size and Species Composition of Zooplankton in Experimental Ponds With and Without Fishes

Comparative studies of artificial ponds with and without reproducing populations of planktivorous fishes provided only qualified support for prevailing ideas on the effects of fish predation on communities of zooplankton. Size and species composition of the zooplankton community as a whole were statistically indistinguishable between pond types. Only when rotifers and copepod nauplii were excluded from the analyses were distinct zooplankton assemblages apparent, with a preponderance of small-bodied forms, especially Bosmina longirostris, found in the fish-containing ponds. Deviations of zooplankton community structure from predictions based on the “size-efficiency hypothesis” may have been due to unanticipated effects of selective feeding by hemipterans and odonate naiads, which were common in the absence of fish.