Spatial and seasonal variation in consumer pressure underlies strong effect of predation in the tropics

Michele F. Repetto and Amy L. Freestone, Department of Biology, Temple University, Philadelphia, PA, Gregory Ruiz and Amy L. Freestone, Smithsonian Environmental Research Center, Edgewater, MD, Carmen Schloeder, Mark E. Torchin and Amy L. Freestone, Smithsonian Tropical Research Institute, Panama

Background/Question/Methods
Biotic interactions are predicted to be stronger in the tropics compared to higher latitudes, contributing to observed patterns of global biodiversity. While increasing evidence suggests predation is stronger at lower latitudes, interaction strengths can be quite variable, and little is known about the extent and the drivers of variability that shape these ecologically important interactions. A variety of factors, including environmental conditions and anthropogenic influence, can contribute to compositional differences in communities of predators or prey and generate increased variability in interaction strength. Here, we test for spatial and seasonal differences in predation across two tropical coastlines (Pacific, Atlantic) of the Isthmus of Panama. We predict that a higher diversity of interacting predators, as we expect to observe in coastal areas of the Tropical West Atlantic, will contribute to a stronger impact of predation. Using standardized experiments focused on communities of sessile marine invertebrate prey and their associated predators, we quantify the impact of predation on prey communities and measure predation intensity with species-specific consumption rates. We also use fishery-independent presence/absence and abundance data collected from locations along these tropical coastlines by the Reef Environmental Education Foundation (REEF) to test for differences in observed fish predator assemblages between coasts.

Results/Conclusions
Our field experiments reveal higher predation rates and stronger effects of predators on prey biomass and composition in Pacific communities, with lower overall levels of predation on the Atlantic. Predation is locally variable in both Pacific and Atlantic communities and influenced by seasonal upwelling regimes in the Pacific. While the observed suite of predators in Atlantic communities is not more diverse than in the Pacific, stronger predation pressure is related to higher diversity at a local and seasonal scale. Further, we find that despite high predator diversity, only a few taxonomic and functional groups contribute to strong signals of predation in these tropical hotspots for predator-prey interactions. Data compiled from extensive REEF dive surveys suggest similar levels of diversity, but disproportionate abundances, across groups of fish predators between coasts. Taken together, these results highlight the importance of diverse predator assemblages and the contribution of individual taxa to the structure and maintenance of tropical communities.