HABITAT VARIABILITY IN THE EFFECTS OF PREDATION AND MICROCLIMATE ON MYCOPHAGOUS FLY COMMUNITIES

Ant predation and soil moisture have direct and interactive effects on the abundance and community structure of mycophagous flies. Here, we replicated an experiment across three climatically different habitat t ypes to describe how these small-scale processes (microclimate and pre dation) are affected by macroclimatic variability at a larger spatial scale (among habitats). Each week for eight weeks during the summer of 1993, 18 Agaricus bisporus mushrooms were placed on dry, moist, or we t potting soil, within predator access or predator exclusion treatment s cups, at six sites in the piedmont of South Carolina, USA. Two sites were moist hemlock ravines and four sites were dry ridgetops, Mushroo ms and soil were collected after one week and fly metamorphs were coun ted and sorted by species, We described the effects of ant predation, soil moisture, site and week on the frequency of host use, metamorph a bundance, and Simpson's diversity. All three measures were affected by macroclimatic differences among sites and across weeks, At wet sites and during rainy weeks, more mushrooms were used, more metamorphs emer ged, and the communities were more diverse than at dry sites or during dry periods. The small-scale effect of soil moisture was strongly aff ected by large-scale macroclimatic conditions. In dry ridgetop sites a nd in dry weeks, abundance and diversity increased with increasing soi l moisture. In moist sites: or juring rainy weeks, however, soil moist ure was unimportant and had no effect on abundance or community struct ure. Predation was unaffected by large-scale differences in climate, h ut was affected by small-scale differences in soil moisture; becoming more intense as soil moisture increased. This research demonstrates th at the effect of climate on predation is a scale-dependent phenomenon, and that microclimatic effects are mediated by climatic conditions at larger spatial scales. We relate these findings re, hierarchical theo ry and hypotheses concerning the relative effects of tolerances, compe tition, and predation under different levels of environmental stress.