The assembly of communities can be shaped pre-colonization by processes like habitat selection as well as post-colonization by processes such as species interactions. The relative importance of processes operating at these two scales for communities that inhabit ephemeral, patchy microhabitats are poorly understood and varies considerably across different systems. We investigated the contribution of different pre- and post-colonization processes to the structure a relatively simple community that depends on an ephemeral microhabitat, the terrestrial egg masses of red-eyed treefrogs (Agalychnis callidryas). The density and location of egg masses, which generally last less than 8 days, are spatially and temporally variable throughout the six-month frog breeding season. Yet egg masses are commonly utilized by a wasp (Polybia rejecta), a fly (Megaselia sp.) and the fly's parasitoid (Figitidae: Eucoilinae). In this study, we examined if colonization patterns of insects were influenced by the spatial aggregation of frog clutches and if the presence of dead or wasp-damaged frog eggs affected fly and parasitoid distribution. Post-colonization, we investigated how intraspecific competition and the availability of different types of resources (i.e. presence versus absence of dead frog eggs) affected fly survival and size.
Results/Conclusions
Our results indicated that, pre-colonization, both the spatial aggregation of egg masses and the presence of frog egg mortality influenced insect presence across clutches. Field data indicated that wasp attacks were concentrated in regions of the pond where frog clutches were laid closer together, whereas fly and parasitoid colonization and abundance were strongly affected by the presence of dead frog eggs but not by near neighbor distance. We confirmed fly preference for clutches containing dead eggs using oviposition site choice experiments. By contrast, there was little evidence that post-colonization processes influenced fly survival. Fly survival was not affected by increasing numbers of conspecific competitors nor by the presence of dead frog eggs. We conclude that local assemblages in this system are more strongly influenced by pre-colonization processes than by post-colonization processes. This research highlights the importance of considering processes operating at different spatial scales when attempting to understand the assembly of communities that inhabit patchy environments and provides insight into how individual behavioral decisions scale up and contribute to patterns of abundance and distribution at larger spatial scales commonly observed in nature.
