Effects of competitors and Chaoborus predation on the cladocerans of a eutrophic lake: an enclosure study

Abstract

The role of large laboratory grown food competitors of the genus Daphnia as well as the predation impact of Chaoborus on the cladoceran community of an eutrophic lake was assessed in five in situ enclosure experiments. The hypothesis tested was that the outcome of competition and gape-limited predation on cladocerans is size dependent. According to the generally accepted assumptions on competition and invertebrate predation, large-bodied cladoceran taxa were expected to be less affected by competing congeners and by Chaoborus than were small-bodied taxa. Effects of the predator upon an assemblage of differently sized cladoceran taxa were much more pronounced than effects of competition. There was a tendency of predation and competition impact to decrease with cladoceran size, but predation pressure was also low for some small cladocerans and high for some large cladocerans. The general trends were further obscured by factors not or indirectly linked to body size.