Effects of grassland fragmentation on insect species loss, colonization, and movement patterns

Ecological theory predicts that isolated habitat patches will experience gr eater rates of species loss and lower rates of recolonization compared to l ess isolated habitats. As a corollary, corridors of suitable habitat should reduce patch isolation, thereby decreasing species loss and enhancing colo nization. Little ecological evidence exists, however, to compare species lo ss and colonization in habitat patches with and without corridors under fie ld conditions. Using insects in a native grassland habitat, I performed a t hree-year field experiment that varied fragment size and connectivity to te st the hypotheses that corridors influence patterns of insect species loss, rates of recolonization, and insect movement among habitat fragments. I de tected few effects of corridors consistent with theoretical predictions. Fi rst, corridors generally failed to reduce insect species loss from otherwis e isolated grassland patches, except for subtle effects in medium-sized pat ches. Species richness was slightly higher in medium patches with corridors than in medium isolated patches when averaged over the three years of the study. I observed the strongest positive effect of corridors in the third a nd driest year of the study. Second, corridors did not significantly influe nce overall rate of patch colonization, but slightly increased the probabil ity of colonization by less vagile species. Interestingly, corridors did no t affect recolonization by rare species, which are often the subject of con servation concern. Third, I characterized individual movement pathways of t hree insect species in plots with and without corridors. One of the three s pecies significantly preferred corridors, while the other two species moved independently of corridors. Taken together, these results suggest that cor ridors have the potential to promote movement of organisms among habitat pa tches, but that their function may depend upon species characteristics, lan dscape context, patch size, and environmental variation.