Trophic ecology of insectivorous bats in agroecosystems.

摘要

Land-use change is a leading cause of biodiversity loss and ecosystem service degradation worldwide, but these changes do not affect all organisms equally. Understanding the factors that influence resistance to environmental change is vital for informed conservation. In particular, dietary generalists may withstand environmental change better than specialists due to their ability to exploit variable resources. Bats are voracious predators of insects, but vary widely in their degree of dietary specialization. In Chapter 1, I analyze the effect of land cover and morphology on dietary diversity and the two most common prey items (Lepidoptera and Coleoptera) of bats, selecting important independent variables using phylogenetic generalized least squares (PGLS) and model selection. Dietary diversity increased with increasing amount of cropland near the study area, consumption of Lepidoptera decreased with increasing habitat diversity, and consumption of Coleoptera decreased with increasing distance from the equator. Biodiversity (and hence, prey diversity) is expected to decrease with agricultural intensity, but the observed pattern suggests that dietary specialists may avoid agricultural habitats due to lack of preferred prey. Dietary specialists may thus be increasingly at risk as agricultural intensity increases around the world, and it is essential that we continue to document their ecological roles and the services they provide to society.;Insectivorous bats consume crop pests in agroecosystems, potentially suppressing herbivory on crops globally. Recent estimates place the value of pest regulating services provided by bats in North America at over three billion USD annually, yet these estimations are built on untested assumptions about top-down effects of bats in row-crop habitats. Specifically, no study has assessed whether bats exert sufficient predation pressure on moth pests to affect 1) density of larvae and 2) herbivory by larvae. In Chapter 2, I provide support for these assumptions and discuss their implications. To test these assumptions, I constructed six large exclosures and paired control plots in corn fields in the Midwestern United States. The exclosures prevented bats from foraging on insects over corn, but were opened during the day to allow birds to forage. I evaluated larval moth abundance and crop damage on 10 plants in each plot every five to six days. I found more moth larvae and crop damage in exclosures than controls, providing the first empirical support for suppression of crop damage by bats in corn. In addition, pest-associated fungal growth on corn was higher when bats were excluded, demonstrating that bats may provide an even more indirect service to agriculture than previously thought. Bats face a variety of threats around the world, but their relevance as predators of insects in a ubiquitous corn-dominated landscape underlines the economic and ecological importance of conserving biodiversity.