Meeting Abstract

P1.25  Saturday, Jan. 4 15:30  Top-down Suppression of Herbivory by Insectivorous Bats in a Midwestern Agroecosystem MAINE, J.J.*; BOYLES, J.G.; Southern Illinois University; Southern Illinois University jjmaine@siu.edu

An important factor mediating ecosystem function is regulation of populations through trophic cascades. Trophic cascades are dampened by compensatory foraging and omnivory, so they mainly transpire in simple ecosystems with distinct trophic levels. Agricultural ecosystems may thus represent an ideal area to assess such interactions. Bats in particular are thought to be important in suppressing crop pest insect populations. Models place the value of pest control services by bats at greater than $3 billion annually, but these models are built on completely untested assumptions about the nature of top-down effects of bats in agroecosystems. Further, many studies suggest that generalist predators cannot provide enough predation pressure to suppress prey populations. To test these assumptions, we directly assessed the strength of pest suppression by bats using six large exclosures and paired control plots in corn fields in the Midwestern United States. The exclosures prevented bats from foraging over corn, but were opened during the day to allow birds to forage normally. Crop pests, crop damage, and bat activity were sampled at weekly intervals. In blocks where crop pest larvae were found, damage was almost universally more severe and crop pests were more prevalent in the exclosure plot than in the paired control. This suggests that insectivorous bats do in fact provide top-down suppression of herbivory in agroecosystems and contradicts assumptions about population regulation by generalist predators.