EFFECT OF HABITAT PATCH CHARACTERISTICS ON ABUNDANCE AND DIVERSITY OFINSECTS IN AN AGRICULTURAL LANDSCAPE

The objective of this study was to test for general effects of patch s ize, patch isolation, disturbance frequency, and patch life span, on d ensity and diversity of organisms. We sampled predominantly herbivorou s insects in 31 alfalfa fields that varied in size, isolation, frequen cy of disturbance by cutting, and age (number of years planted in alfa lfa). Effects on insect relative density and diversity were examined a t three taxonomic levels: all insects, eight separate orders, and six legume-specialist weevil species. We found that (a) more isolated alfa lfa fields had higher overall insect richness, (b) fields with higher disturbance frequency had lower overall insect richness, and (c) field s of intermediate age had highest insect richness. In some cases these patterns were reflected at lower taxonomic levels, but in many cases they were not. These results are important because they indicate that, although we cannot simultaneously tailor a landscape for each of thou sands of species, we may be able to produce desired effects at a more general level.