Document: CHR-3-56-10

The effects of prey heterogeneity and consumer identity on the limitation of trophic-level biomass.

STEINER, C.F.*

W. K. Kellogg Biological Station, Hickory Corners, MI 49060 ¹

Abstract:
Models of keystone predation suggest a central role of prey heterogeneity in determining the strength of predator interactions and patterns of trophic structure along productivity gradients. If trade-offs exist among prey in predator resistance and competitive ability, increasing productivity can permit prey turnover (favoring resistants), consequently dampening predator limitation and allowing increases in total prey biomass. Furthermore, in aquatic systems, limitation of algal communities is thought to hinge on zooplankton-predator identity. Compared to small species, large-bodied Daphnia are thought to be stronger interactors with algal-prey. I investigated the roles of consumer size and prey heterogeneity on trophic structure by performing a controlled laboratory experiment using 18-liter enclosures and a model aquatic community. In this study, I created a simple food chain comprised of a single edible prey, and a food web comprised of a diverse assemblage of algal-prey. I then fully crossed these two treatments with two predator treatments (large Daphnia versus small Ceriodaphnia), and two levels of productivity. Results provided clear support for the keystone predator model. Predators had strong negative effects in food chains and algal-prey biomass exhibited no response to enrichment. In contrast, predator limitation was weak in food webs with the consequence that predator and prey biomass both showed positive increases with productivity. The prey community in food webs also exhibited a striking increase in the relative abundance of large inedible algae with enrichment, in keeping with model predictions. Predator identity had little effect on prey composition or overall prey biomass in both food chains and food webs. These results indicate that prey heterogeneity can have substantial effects on trophic structure and can serve to shift systems from strong top-down limitation to ones in which prey are co-limited by predator and resource effects.

Keywords: keystone predation, top-down versus bottom-up limitation, predator-prey interactions

This abstract is being presented at: 2:15 PM in session:
Oral Session #47: Zooplankton Ecology.