Investigating the indirect effects of fish community assemblage in Trinidadian streams on populations of a shredding caddisfly

Non-consumptive effects of predators can have important roles in shaping characteristics of prey populations. In Trinidad, streams can have upstream reaches with only killifish (Anablepsoides hartii) at higher densities, separated by large barrier waterfalls from downstream reaches containing both guppies (Poecilia reticulata) and killifish at lower densities. Larvae of a leaf-shredding caddisfly, Phylloicus hansoni (Trichoptera: Calamoceratidae), experience predation from killifish in these streams. Previous research has shown lower abundances of Phylloicus in killifish-only reaches, suggesting increased predation pressure where guppies are absent. We studied Phylloicus populations to determine whether differences in fish community also drive shifts in life history and leaf-shredding behavior in these streams. We collected Phylloicus larvae from five streams with distinct killifish-only (KO) and killifish+guppy (KG) reaches to compare size frequency distributions. We also performed a laboratory experiment to assess behavior of KO and KG Phylloicus in the presence of killifish. Larvae from KO reaches show a size frequency peak at a smaller size than KG reaches and appear to respond differently to predators, in terms of shredding activity. More research is needed to determine whether size-selective predation or changes in growth rate are driving the differences in size structure of this functionally important aquatic insect species.