Animal mediated seed dispersal is a key ecosystem function that influences biodiversity maintenance by regulating the flow of plant genetic material among habitat patches. Co-evolution and climate can influence the diversity and composition of species interactions in seed dispersal networks. Co-evolutionary trait relationships promote or prevent interactions between coexisting plant and animal populations. Deterministic assembly processes shaping multispecies coexistence along environmental gradients can differ between plant and animal trophic levels. Such assembly differences can derive in patterns of plant and animal functional trait diversity which are more asymmetric than the ones expected from coevolution and stochastic assembly alone. Here, we ask to what extent spatial and seasonal variability in temperature and precipitation shape functional trait asymmetries of seed dispersal networks between palms and mammal frugivores in the Neotropics. Using functional traits of interacting palms and mammalian frugivores in the Neotropics, we predict a metaweb of seed dispersal interactions and project it over a spatial grid, we then measured spatial changes in functional asymmetry and network structure. Finally, we model the effects of temperature and precipitation gradients in functional asymmetry, as well as the influence of functional asymmetry in the modular and nested structure of seed dispersal networks.
Results/Conclusions
We developed new metrics to measure changes in functional trait asymmetry, functional size asymmetry, and functional spacing asymmetry. The first indicates whether constraints on assemblage-wide niche breadth differ between trophic levels. The second indicates whether the magnitude of interaction niche differentiation differs between trophic levels. Interpreted together, these metrics reflect differences in how species from distinct trophic assemblages perceive their potential to form trophic interactions. In other words, the asymmetry of functional interaction niches. Functional asymmetry between palms and mammal frugivores was greater in arid and seasonal regions than in tropical humid regions of the Neotropics. In more arid and seasonal regions, the predicted structure of interaction networks was less nested and less modular. Although spatial and seasonal gradients in temperature and precipitation influenced both functional asymmetry and network structure of palm and mammal assemblages, there was significant variation in functional asymmetry and network structure among biogeographic dominions which could be the result of spatially uneven patterns of extinction and diversification of palms and mammal frugivores in the Neotropics. Our results can help predict the effects of global climate change in the structure of palm seed dispersal networks, which are of fundamental importance for the maintenance of tropical ecosystems.
