Dispersal and edge behavior in a bark beetle and its predator

Bark beetles are major pests of pine forests in North America. One of their main predators, Thanasimus dubius (Coleoptera: Cleridae), could potentially affect bark beetle dynamics and there has been increasing interest in the ecology of this predator. In the present study, we measured the dispersal abilities of both T. dubius and one of its prey, Ips grandicollis (Coleoptera: Curculionidae: Scolytinae), and then examined their behavior along an edge between pine forest (habitat) and clearings (non-habitat). We quantified the dispersal ability of T. dubius relative to its bark beetle prey using mark-recapture methods and a diffusion model. The mark-recapture experiments involved the release of marked individuals at 3 different field sites in Wisconsin. At each site, traps were deployed up to 2 km distance in a cross-shaped pattern. We investigated edge behavior using a transect of traps extending from pine forest into clearings at 5 field sites. Our results indicate that a third of predators disperse farther than 2 km, while most I. grandicollis remain within 0.5 km of the release point. The transect data suggest strong edge behavior in T. dubius, because relatively few individuals were found in clearing vs. pine forest, while the distribution of I. grandicollis was more homogeneous. Although T. dubius apparently has greater dispersal abilities than I. grandicollis within pine forest, its spatial distribution may also be restricted by edge behavior.