Fish foraging and learning in complex environments

This study assessed the influence of prey assemblage and habitat complexity on foraging and learning in sunfish. I assessed the relationship between fish foraging and learning and three aspects of complexity: (i) complexity in the prey assemblage due to variation in density and species composition, (ii) complexity in the physical structure of the habitat due to the presence of aquatic macrophytes and (iii) complexity due to variation in the prey assemblages experienced over time.;The first relationship was examined by comparing fish foraging success in one-prey (Daphnia) and two-prey trials (Daphnia and Chaoborus). Experience was imposed by repeatedly exposing fish (Lepomis gibbosus) to the same prey assemblage. Foraging in complex prey assemblages was found to carry a cost (i.e., reduced foraging efficiency), but fish partially overcome this cost with experience. The less energetically valuable prey in a mixed-species prey assemblage created a confusing environment making it difficult for fish to select only the most energetically rewarding prey. However, experience resulted in increased total biomass consumption as fish learned to select the larger, more energetically valuable prey. Furthermore, learning was greatest at intermediate levels of prey assemblage complexity.;The second relationship was tested by comparing foraging and learning by different sizes (small and large) and species (bluegill and pumpkinseed) of sunfish in simple versus structurally complex habitats (i.e., with and without vegetation). The results support the hypothesis that structural habitat complexity influences foraging and learning in sunfish. I found that size-specific differences in foraging success can arise from size-specific differences in learning. Initial habitat-specific differences in foraging success became more pronounced with experience. Moreover, my results are consistent with the hypothesis that habitat-specific learning reinforces habitat specialization. Specifically, fish showed the greatest improvement in foraging success in the habitat (either vegetated or open-water) in which they are predominately found in the field.;Finally, I examined the relationship between fish foraging and learning and variation in prey assemblages over time. I studied bluegill sunfish (Lepomis macrochirus) foraging under conditions of either low or high variance in the composition of the prey assemblage over time. The results support the hypothesis that variance in the prey assemblage experienced over time influences fish foraging and learning. Fish showed the greatest learning potential in treatments with the highest density of the preferred prey. The effect of variance was greatest at intermediate total prey density, where fish trained in high variance treatments consumed less total biomass than fish trained in low variance treatments. Finally, the overall density of the preferred prey had a greater influence on learning than did the density of the less preferred prey or variance in the prey assemblage over time.