ZOOPLANKTON MIGRATION IN 3 LAKES OF WESTERN NEW-YORK

We examined the diel vertical migration (DVM) of zooplankton in three lakes of western New York; Lakes Conesus, Lime, and McCargo. In all th ree lakes, the dipteran predator Chaoborus was a more dramatic migrato r than any of the cladocerans or copepods. In contrast, another invert ebrate predator, Leptodora, seemed to have the least vertical dispersa l. In Conesus Lake, following the evening ascent and upper-water night -positioning of Chaoborus flavicans, Daphnia pulicaria expanded its ow n vertical range of dispersal thereby decreasing its degree of overlap with Chaoborus. The vertical distribution of Diaptomus sicilis was mo stly below that of Daphnia pulicaria, thus reducing possible competiti on for food resources. Poor oxygen conditions in the lower waters of L akes Lime and McCargo restricted all zooplankton (except Chaoborus) to an epilimnetic zone where the regions of niche overlap and predation were narrowed. Such annually-induced restrictions on vertical dispersa l are probably common features of numerous stratified lakes with hypol imnetic reducing conditions. No fixed pattern of vertical dispersal or migration is likely in lakes where stratification and non-stratificat ion follow each other seasonally. Vertical migration does provide some flexibility in niche separation, but the potential for chaotic behavi or in interacting predators and prey may confound simple explanations of DVM.