Host plants as islands: Resource quality and spatial setting as determinants of insect distribution

Both the quality and spatial configuration of a habitat can affect the distribution of its inhabitants. However, few studies have directly compared the relative effects of the two. In this paper, we focus on spatial patterns in the distribution of an oak-specific moth, Tischeria ekebladella. At the landscape level, the species was more often present on well-connected trees than on isolated trees. Experimental transplants revealed pronounced variation in larval survival among individual leaves within trees. In fact, survival on a “good” and a “bad” leaf within a tree differed almost as much as survival between a “good” and a “bad” leaf chosen randomly on two different trees. Qualitative differences among trees did not explain the distribution of the species across the landscape, as average larval performance did not differ between trees naturally occupied and unoccupied by the species. Hence, spatial effects seem to dominate over host tree quality in determining the regional distribution of Tischeria ekebladella.