Print PageIntraguild predation (IGP) is an interaction in which predators that compete for the same resources also interact as predator and prey themselves. The simplest form of IGP occurs between a top predator, intermediate predator, and shared prey and IGP relationships have been observed and studied extensively in larval invertebrate communities in ponds. Past studies have produced conflicting results concerning the effect of prey density on IGP interactions, which may be due to the variation in spatial scale of experimental mesocosms. To examine these differences, an experiment was conducted using dytiscid water beetle larvae (Dytiscus species) as the top predator, larvae of the dragonfly Anax junius as the intermediate predator, and smaller larvae of the dragonfly Sympetrum semicinctum as the shared prey. Spatial scale of the mesocosms and density of shared prey were manipulated to determine their effects on intermediate predator (A. junius) mortality and IGP relationships.
Results/Conclusions
Shared prey density was significant; A. junius mortality was greatest in treatments with no shared prey and intermediate shared prey density, but less in treatments with low and high shared prey densities. Spatial scale was marginally significant for A. junius mortality. S. semicinctum mortality, however, was significantly affected by spatial scale but not affected by density. Foraging strategies and other behavioral changes likely account for mortality differences. These results advance our understanding of spatial scale in IGP relationships with different shared prey densities. Ultimately, a better understanding of the effect of experimental spatial scale in will help ecologists design small-scale experiments that more accurately represent natural ecosystems.
