Efficiency of area-concentrated searching behaviour in a continuous patchy environment

Abstract

In many natural situations involving terrestrial predators, prey items are clustered in patches that have no perceptible boundaries and can only be defined as areas where the local resource density is higher than the mean overall resource density. In this type of continuous patchy environment, an efficient forager has to regulate the sinuosity (klinokinesis) and the speed (orthokinesis) of its random search movements so as to concentrate its search effort in the high resource density areas. This study determined the theoretical efficiency of this area-concentrated behaviour using computer simulations. Two search modes were assumed to be used by the model predator: an intensive search mode involving high sinuosity and low speed within high resource density areas, which is triggered by the detection of a prey item, and an extensive search mode involving low sinuosity and high speed between these areas, which is resumed after an unsuccessful search. Among the four habitat types included in this study, the efficiency of this movement control was higher in coarse-grained than in fine-grained habitats and increased also with the level of heterogeneity. The optimal values of the movement control parameters were similar whatever the habitat type and a large range of values led to nearly maximal efficiency. This suggests that even if they can only poorly estimate the resource distribution, terrestrial predators may ultimately search efficiently for clustered prey items by using elementary proximate mechanisms roughly controlling their random search movements.