Habitat fragmentation alters predator satiation of acorns

Acorn weevils (Curculio spp.), endoparasitic granivorous insects, impede recruitment of fagaceous trees, and in turn affect community structure and ecosystem functioning. Previous studies have made considerable progress in elucidating local factors that contribute to seed predation by acorn weevils, but it is still not clear how habitat configurations interplay with local factors in influencing Curculio predation. In this study, we assessed the roles of crop size, landscape configurations (area and isolation) and their interactions on the predation rate of seeds by acorn weevils. Methods We studied acorn weevils feeding on the seeds of Castanopsis sclerophylla (Fagaceae) on two peninsulas and nine islands with varying areas and isolation levels in the Thousand-island Lake in Chun-an County, Zhejiang Province of China. Overall, crop size was estimated for 130 trees and predation status was assessed for 26 207 seeds from these trees during two years. Generalized linear mixed models were performed to clarify how island area and isolation interplayed with crop size to determine predation rate on a single tree. Important Findings A negative relationship was detected between crop size and seed predation rate, indicating predator satiation at the tree level. This suggests that acorn weevils tend to stay sedentary once they have arrived at a suitable habitat. Habitat fragmentation had significant effects on seed predation such that predation rate was higher on larger, less isolated islands. Furthermore, the relationship between crop size and predation rate was significantly changed by both island area and isolation. This finding highlighted that the effects of habitat isolation might be overlooked relative to those of habitat loss.