Spatial structure, not prey distribution, is the most important determinant of predator foraging success

Background/Question/Methods

Almost all studies and theory of predator foraging focus on the effects of prey patchiness and density in determining consumption rates. However, common sense, and mathematical analysis suggest prey encounter rates will be altered in spatially complex environments that modify movement paths. We demonstrate that not only does environmental structure determine predator foraging rates, it is a much more important predictor of success than prey distribution. We studied the consumption rate of ladybugs (Harmonia axyridis) foraging for pea aphids (Acyrthosiphon pisum (Harris)) under 2 conditions of prey distribution (aggregated and uniform), and in two types of spatial environments (a 2D circular structure of pea tissue and 3D pea plants). 
Results/Conclusions

Predator consumption rates were significantly greater in the simple spatial environment, even though the surface area of the plant tissue was the same in both treatments. On the more complicated spatial structure of  pea plants, aphid distribution had no significant effect on ladybug intake rates. In the simple environments, predator intake rates were slightly lower when prey had an aggregated distribution. We conclude that estimates of predator efficacy in the field which are based on laboratory studies that use simple spatial environments are highly suspect. More generally, studies which emphasize the effects of prey distribution on foraging success may provide relatively little insight into ecological relationships given the very strong effects of environmental structure.