Document: MAR-3-56-29

Predator-prey ratios: Multiple tests of the invariance rule.

VINSON, M.R.* and T.A.CROWL

Utah State University, Logan, UT 84322, U.S.A. ¹

Abstract:
The number of predator and prey taxa in ecological communities have been observed to be highly correlated with the ratio of predators to prey and is largely invariant across taxa assemblages, community food webs, and different habitats. Based on more than 4600 samples collected in freshwater habitats across western North America and for ratios calculated for all North American freshwater insect genera we show that lentic habitats (wetlands, ponds and lakes) support more than twice as many insect predator taxa per insect prey taxa as do lotic habitats (fluvial springs and rivers). The numbers of predator and prey genera were highly correlated, but the mean predator-prey ratio varied significantly and considerably between lentic and lotic habitats. For field samples, the mean predator-prey ratio was 1.160.07 SE, (0.9 prey genera per predator genera) for lentic habitats and 0.390.004 SE (2.6 prey genera per predator genera) for lotic habitats. For all North American aquatic insect genera, the ratios were: 1.13 for lentic habitats and 0.43 for lotic habitats. Lentic and lotic waters had similar numbers of genera classified as predators, but lotic waters had 2.3 times more genera classified as prey than did lentic waters. We suggest that differences in the predator-prey ratio between lentic and lotic waters are related to body size that promote different species compositions in response to hydrodynamic stresses and dispersal dynamics that affect rates of colonization and extinction.

Keywords: Predator-prey ratios, aquatic insects, freshwater ecosystems

This abstract is being presented at: 1:00 PM in session:
Oral Session #67: Decomposition Processes.