Effects of habitat configuration on host–parasitoid food web structure

Abstract

AbstractThe dispersal of organisms among patches affects community structure in spatially heterogeneous habitats. The enhancement of dispersal frequency among patches can be expected to increase potential interaction between organisms in food webs. However, it has been difficult to fairly evaluate the effects of dispersal on the food web structure because the quantification of actual dispersal is difficult. In this study, in order to manipulate the dispersal frequency, two oak plantations (each with 100 oak trees) were established as high‐patch connectivity (1‐m interval) and low‐patch connectivity (3‐m interval) plots. Quantitative food webs of herbivores and their parasitoids were constructed for the high‐ and low‐connectivity plots, and quantitative measures of food web metrics as indices of structure were calculated for both webs to examine dispersal effects on food web complexity. In the entire web, 86 herbivore species (Lepidoptera and Coleoptera) were attacked by 50 parasitoid species (Hymenoptera and Diptera). As a result, although we found no significant difference in herbivore abundance between high‐ and low‐connectivity plots, a higher parasitism rate and greater complexity in web structure were observed in many food web metrics for the high‐connectivity plot. Furthermore, the parasitoid overlap diagram showed a higher potential for indirect interactions among herbivore species in the high‐connectivity plot. These results imply that the increase in dispersal frequency among habitat patches facilitates food web complexity, and the role of dispersal as a determinant of food web structure should be considered in food web ecology.