Replacement of herbivore zooplankton species along gradients of ecosystem productivity and fish predation pressure

In general the pooling of major taxa did not provide a basis for classifying zooplankton communities in 342 large Norwegian lakes, as neither cladocerans nor calanoids varied systematically with lake productivity or fish predation pressure. At the species level, most herbivorous cladocerans and calanoids, which constituted three quarters of the metazoan zooplankton biomass, differed in their preference for lake productivity and fish community. Analysis pointed out one oligotrophic and one eutrophic specialist among the herbivorous cladocerans; two calanoids were oligotrophic specialists. At low lake productivity, chemical variables such as pH and Ca, as well as the species' physiological adaptations, are the main determinants for the comptetitive advantage and relative success of herbivorous species. Fish community composition changes with increasing lake productivity, but only at very high fish predation intensity (cyprinid communities) did the effects of predation become the main determinant of the zooplankton community, superimposed on the lake productivity. -from Authors