Document: KEN-3-52-15

Differential responses of forest-floor arthropod predators and prey to long-term detrital subsidy.

LAWRENCE, K.L.* and D.H.WISE

University of Kentucky, Lexington, KY 40546 USA ¹

Abstract:
We investigated the impact of long-term detrital subsidy on densities of arthropod generalist predators and prey in forest-floor leaf litter. We wanted to know if an increase in the resource base would lead to persistent, uniform increases across all trophic levels; or to differential responses of major groups of predators and prey. Uniform increases would suggest that bottom-up forces dominate in determining food web structure. Differential responses among detritivores, fungivores, and predators would indicate that top-down forces play a significant role in determining food web structure in this widespread detrital food web. Twenty plots were randomly assigned to one of four treatments in a 2x2 design: Open; Open + Detritus; Fenced; and Fenced + Detritus. We added high-quality detritus to the detritus-addition plots every 14 days from April to October of 1997, 1998, and 1999. Densities of all major groups of detritivores, fungivores, and generalist predators - Collembola, fungivorous Diptera, spiders, pseudoscorpions, and centipedes - increased in response to detrital enhancement within the first 4-12 months - indicating short-term, bottom-up limitation. The long-term subsidy revealed differential responses. After increasing initially, tomocerid Collembola, web-building spiders, and pseudoscorpions decreased to, or below, control levels - suggesting that long-term equilibria differ from the initial increases in density. This pattern of differential, long-term responses suggests that both bottom-up and top-down control processes contribute to trophic dynamics in this food web.

Keywords: generalist predators, top-down control, bottom-up control, detrital, field experiment, trophic dynamics, spiders, Collembola

This abstract is being presented at: 11:00 AM in session:
Oral Session #44: Terrestrial Invertebrates: Foodwebs and Plant Responses.