Fig-frugivore interactions follow a constrained Brownian motion model of evolution in an important bird area, West Africa

Understanding how ecosystems function is critical in order to shed light on processes that lead to species coexistence. Ficus species provide highly specialized niches for frugivores in tropical forests, but little is known about how Ficus-hugivore interactions evolve over time. Here we applied three approaches to investigate these interactions based on key parameters. We tested for a model of evolution that could explain interaction patterns, evaluated the phylogenetic signal, and assessed the evolutionary rate of niches generated by Ficus species. We showed that interactions are best explained by a Brownian motion model, indicating a random walk. However, the signal observed is lower than expected under this model, and at the same time the evolutionary rate provides evidence for niche conservatism. Such findings are incompatible with an unbounded Brownian process. We therefore propose that a random walk constrained by ecological forces towards a stabilizing selection could better explain fig-frugivore interactions in tropical forests.