Top-down effects of damselfly larvae on the phylogenetic structure of the invertebrate community of bromeliads

In this study, we take an experimental approach to assess the effects that the presence of predators has on the phylogenetic structure of prey communities. We use the aquatic invertebrate community of bromeliads as our study system. Bromeliads' aquatic ecosystem harbors delimited invertebrate communities that encompass complex trophic networks. Damselfly larvae are the top predator of the system. They affect the prey community composition and can potentially change its phylogenetic structure. Generalist predators can affect the prey community by increasing the extinction risk of prey species with a particular trait or by preventing the colonization of species that can detect and avoid colonizing bromeliads with predators. If these traits are phylogenetically conserved, predator presence should lead to a clustered phylogenetic pattern in the prey community. However, habitat filtering – in this case, small bromeliad sizes– can result in a similar phylogenetic pattern by increasing the death risk of species with low drought tolerance. To disentangle the effects of both factors, we designed experiments in the field manipulating the presence/absence of predators along a gradient of bromeliad size and in different phases of the community assembly process: colonization and extinction. We also surveyed natural communities to compare these patterns. We use GLMs and SEM to assess the effects that predators and habitat size have on different phylogenetic metrics of the community. Our preliminary results show that smaller habitat sizes have a stronger clustering effect on the community than the presence of predators and that these effects differ among invertebrate clades.