Effects of Bird Predation on Grasshopper Densities in an Arizona Grassland

作者：Carl Ernst Bock, Jane H. Bock, Michael C. Grant · 发表于：Ecology · 年份：1992 · DOI：10.2307/1940022 · 被引用次数：129 · 研究领域：Ecology and Vegetation Dynamics Studies、Plant and animal studies、Animal Ecology and Behavior Studies

In a 4—yr field experiment, we tested the hypotheses that insectivorous birds (1) controlled densities of herbivorous grasshoppers in an ungrazed semiarid grassland in southeastern Arizona, and (2) functioned as keystone predators, by limiting abundances of grasshoppers that otherwise might change vegetation cover and species composition, and/or by mediating the effects of otherwise competitively superior members of the grasshopper assemblage. We measured grasshopper densities and vegetation on 32 464—m2 grassland plots for 1 yr, then enclosed 16 of these plots with bird exclosures and continued data collection for 3 yr. Eight of the 16 experimental plots were further modified in the last 2 yr of the study by installing fine—mesh 1 m high barriers designed to retard grasshopper dispersal. Microclimates of caged plots differed only slightly from open plots. Lizards and rodents increased inside the exclosures, but they were removed and released elsewhere such that their average abundances did not differ among treatments. By the final year of the study, mean annual adult grasshopper density was >2.2 times higher on plots from which birds were excluded, and where grasshoppers were enclosed by dispersal barriers, than on unmanipulated control plots. Mean nymph density was >3.0 times higher in the same comparison. Grasshoppers were significantly more abundant in bird exclosures with insect dispersal barriers, indicating that experimental plots were dispersal sources rather than sin...