COS 50-4 - Evolutionary history and environmental changes shape trophic interactions of tropical mammals

Abstract: Tropical regions harbor the most diverse terrestrial mammal species on the planet and support similar niche spaces resulting from convergent evolution. Tropical mammals may have evolved into narrower niches, including specialized resource niches, through niche-filling in stable, productive, and biodiverse environments. Yet how evolutionary history, paleoenvironmental changes, and human impacts have shaped consumer-resource interactions in tropical mammal food webs worldwide is unknown. We quantify the trophic structure of tropical mammals worldwide and investigate the relative effects of evolutionary history, environmental changes over deep time, and human impacts on mammal trophic structures using regression models. We compiled the first tropical mammal absence-presence of consumer-resource interactions from published communities and literature for the Neotropical (N=118), Afrotropic (N=163), and Indomalayan (N=105) regions. We quantified trophic structures and estimated resource specialization from two food web-level metrics. Specifically, for response variables, we used resource linkage density (i.e., number of linkages divided by the number of consumer species) and resource hypervolume (i.e., hypervolume of multidimensional trait space of resource species), with increasing values for generalization in quantity and niche breadth of resource species. By integrating species-level time-calibrated phylogeny and global environmental spatial data, we estimated speciation rate, paleoenvironmental changes in climates and land covers, seasonality in climate and productivity, environmental heterogeneity in elevation and habitat, and human impacts as explanatory variables for each community. We then applied a regional-specific spatial simultaneous autoregressive error model for each food web metric. We observed comparable mean trophic levels worldwide but a lower proportion of intermediate species in the Neotropics, along with higher speciation rates in relation to other tropical regions. These findings suggest broad energy constraints on trophic levels but different biogeographic histories among regions. Regional-specific regression results further indicated that different dominant evolutionary and environmental factors shaped trophic structures among regions. In the Neotropics, speciation rate was the only significant predictor of resource generalization at the food-web level, suggesting trophic niche filling after extinction events in the Pleistocene, such as glaciations and the Great American Biotic interchange. In the Afrotropics, contemporary climatic and productivity instability were significantly predictive of resource generalization. In the IndoMalayan regions, increasing speciation rate and elevation range were significantly associated with resource generalization, while climatic instability over deep time was significantly predictive of resource specialization. Our findings provide insight into the formation of trophic interactions of tropical mammals and potential regional stressors for altering their trophic structures in the changing world.