Effect of canopy openness on the pressure of predatory arthropods and birds on epigeic insects

As canopy structure produces spatial heterogeneity of litter microclimatic conditions and thus is a crucial factor affecting ground insects, we hypothesized that low canopy openness has a positive effect on the activity of ground insect predators in forest and non-forest habitats. Blowfly larvae were used as bait along the canopy openness gradient (forest interior, forest edge, base of a solitary tree and meadow) and the attack rate was assessed after 30 min of exposure. Although the predation rate has a varying pattern throughout the year in different habitats, in contrast to previous studies, we observed a significant positive trend in predation rates toward the forest interior. A significant trend in predation rate was not observed in non-forest areas. We found that the trend was strongly influenced by ants as the most active taxon of predators (65%) attacking our baits, whereas ground beetles, the second-most active predators (21%), showed the opposite trend along the canopy openness gradient.