Thursday, August 5, 2010: 9:00 AM
303-304, David L Lawrence Convention Center
Background/Question/Methods Species interactions are widely assumed to be stronger at lower latitudes. But while many studies have explored this hypothesis using focal species, a shift in aggregate interaction strength with latitude will also have important consequences for community assembly and emergent patterns of species diversity. Previous studies have demonstrated that predation can impose a deterministic ecological filter during assembly of prey communities by reducing the realized species pool available for colonization and recruitment. In turn, this effect should surface in patterns of community similarity at the local scale, with predation potentially limiting not only species richness, but also composition. If predation is stronger at lower latitudes, then these effects should be more severe in the tropics than the temperate zone. We conducted predator exclusion experiments on communities of sessile marine invertebrates in four regions in the western Atlantic Ocean and Caribbean Sea. Species occurrence and abundance data were analyzed to explore the impact of predation among treatments and latitudes on species richness and community similarity.
Results/Conclusions While predation shaped community structure in both the temperate zone and the tropics, impacts were more striking in the tropics. Tropical communities were two to over ten times more species rich in the absence of predators than when predators were present. In contrast, predation had no effect on species richness in the temperate zone. Effects of predation on temperate communities emerged in analyses of community similarity, although effects were still stronger in the tropics. In both temperate (Connecticut, 41°N) and tropical (Panama, 9°N) regions, communities were more similar within the same treatment than among treatments. This result demonstrates that species sorted in response to predation at both high and low latitudes. In Panama, however, predation also reduced the observed variability in species composition. Therefore, communities that assembled in the presence of predators were more similar (lower beta diversity) than those that assembled in the absence of predators (higher beta diversity). Furthermore, species observed in the presence of predators in Panama represented only a subset of the total observed regional species pool. Differences in within-treatment variability in species composition and a reduced species pool in the presence of predators were not observed in Connecticut. These results are consistent with the prediction that predation exerts a stronger ecological filter on community assembly in the tropics than the temperate zone and impacts species diversity patterns at multiple scales.
Results/Conclusions While predation shaped community structure in both the temperate zone and the tropics, impacts were more striking in the tropics. Tropical communities were two to over ten times more species rich in the absence of predators than when predators were present. In contrast, predation had no effect on species richness in the temperate zone. Effects of predation on temperate communities emerged in analyses of community similarity, although effects were still stronger in the tropics. In both temperate (Connecticut, 41°N) and tropical (Panama, 9°N) regions, communities were more similar within the same treatment than among treatments. This result demonstrates that species sorted in response to predation at both high and low latitudes. In Panama, however, predation also reduced the observed variability in species composition. Therefore, communities that assembled in the presence of predators were more similar (lower beta diversity) than those that assembled in the absence of predators (higher beta diversity). Furthermore, species observed in the presence of predators in Panama represented only a subset of the total observed regional species pool. Differences in within-treatment variability in species composition and a reduced species pool in the presence of predators were not observed in Connecticut. These results are consistent with the prediction that predation exerts a stronger ecological filter on community assembly in the tropics than the temperate zone and impacts species diversity patterns at multiple scales.