Award: OCE-1434528

This project established an international research collaboration, involving over 40 researchers and students across three countries and five institutions, to understand how fundamental species interactions can shape marine communities across latitude. We conducted a series of year-long manipulative experiments in nearshore marine communities along the Pacific coast of North and Central America. Experiments were conducted at 12 sites in four regions spanning the tropics to the subarctic, representing one of the largest marine experiments in nearshore environments. Using multiple lines of evidence, our results support the long-held hypothesis that predation is more intense and has stronger impacts on prey communities in the tropics relative to higher latitudes. We found that predation shaped patterns of community biomass and composition in tropical Panama, with weaker effects of predators in subtropical Mexico, and no measurable effects in temperate California or subarctic Alaska. Using direct observations of the predator community, we documented predation rates in Panama that were an order of magnitude greater than in Alaska or California. Despite the intensity of predation in the tropics, our observations of both predator activity and interaction outcomes suggest high spatial and temporal variability in predation pressure on the Pacific coast of Panama. Additional experiments demonstrated that the effects of predators are more intense on the Pacific in comparison to the Atlantic coast of Panama, suggesting variability in predation pressure between tropical ocean basins as well. We further found that predation reduced non-native species abundance on the Pacific but not the Atlantic coast of Panama, suggesting that intense predation in the tropics has the potential to shape patterns of biological invasions. Results also suggest that competition may be stronger at higher latitudes, demonstrating that competition and predation may covary in their intensity at a biogeographic scale. Our collaboration trained one postdoctoral scholar and 28 early-career professionals and students ranging from high school to graduate school. We disseminated the results of our research to the scientific community through over 28 conference presentations and a growing list of peer-reviewed papers in the scientific literature. Our team actively engaged in numerous outreach activities with K-12 school children and teachers, demonstrating both the scientific principles of our research and the applications to biological invasions. This project also catalyzed a cross-hemisphere international research initiative, entitled PanAmEx: Pan-American Experimental Initiative in Marine Macroecology, led by Smithsonian's Marine Global Earth Observatory, Smithsonian Environmental Research Center, Smithsonian Tropical Research Institute, and Temple University. PanAmEx is a collaborative network to examine broad-scale ecological patterns and processes across coastal marine ecosystems of North, Central, and South America, spanning nearly 40 sites, two hemispheres, and two ocean basins. Last Modified: 11/26/2019 Submitted by: Amy L Freestone