Influence of leaf detritus quality and risk of predation on the behavioral patterns of Phylloicus sp. (Trichoptera: Calamoceratidae)

Abstract

Predation can generate a cascading effect (top-down control) within the aquatic food web. On the other hand, the bottom-up control can also significantly influence the behavior patterns of shredders, especially on their leaf-shredding activity. We aimed to assess the individual and interactive effects of the predation risk by fishes from the genus Astyanax and the quality of leaf discs in the behavioral patterns of shredders from the genus Phylloicus (Trichoptera). The experimental design consisted of two levels of predation risk (absence and presence) and two levels of quality of leaf discs (high and low) in three experimental blocks. All experiments were run for nine days. Our results showed that the quality of the leaf discs affected the percentage of the general body movements of Phylloicus sp, with these caddisflies foraging for more extended periods in the presence of high-quality leaf discs. Moreover, the presence of invertebrates in cases can be influenced by the detritus quality and the interaction between predation risk and detritus quality. Therefore, the predation associated with low-quality nutrition might affect the behavioral patterns of Phylloicus sp., reflecting a shorter time spent in the construction of its larval case, which might lead to higher predation. This might explain this functional feeding group's low abundance and density in tropical streams. On the other hand, their capacity to consume their larval case could be an adaptative advantage over other shredders. Still, more field and microcosm experiments are necessary to arrive reality of tropical streams. We showed a way to explain the natural selection of this species and how interactions are running now.