Influence of prey distribution on the functional response of lizards

We experimentally examined the effect of invertebrate prey distribution on the functional response of a vertebrate predator. We predicted how predator consumption of prey would change with prey distribution using a scale-dependent foraging model. This model predicted that prey consumption rate should decrease as a fixed density of resources becomes more dispersed in space as measured by its fractal dimension. The model incorporates an explicit description of the spatial distribution of prey into classical optimal foraging theory. We tested this prediction with foraging trials involving lizards feeding on grasshoppers in experimental arenas with a single grass species as vegetation cover. We manipulated grasshopper distribution associated with this grass by manipulating the distribution of vegetation in arenas to yield different fractal dimensions. Skinks foraging in arenas with a few large clumps of vegetation (low fractal dimension) captured significantly more prey at all prey densities than skinks foraging in arenas with many small clumps but not necessarily more evenly dispersed (high fractal dimension). These results support the predictions of the spatially dependent foraging model, and show that prey dispersion can strongly modify the predator functional response.