Intrinsic and extrinsic drivers shape frugivore functional diversity within a tree population

Abstract

In sessile organisms like plants, interactions with strong fitness implications, such as seed dispersal, are influenced by individual traits and the surrounding environmental context. Recent studies have revealed that individual variation in plant populations shapes mutualistic interactions, but the focus often remains on the taxonomic diversity of partners. We examined how intrinsic (phenotypic and phenological traits) and extrinsic (spatial context) drivers of differences in individual plants influence the multidimensional functional diversity of frugivorous birds. Our study system was a native plant population of Schinus terebinthifolia, a species that is invasive worldwide and whose fruits are highly attractive to birds. Despite the limited functional differentiation among the most common generalist frugivores, our findings demonstrate that plant phenotypic traits and local environmental conditions distinctly influence multiple facets and dimensions of avian alpha diversity. Tree height increased functional richness and divergence, while human infrastructure reduced both indices. Crop size had positive effects on functional divergence and regularity, and tree cover reduced functional richness. Most effects, particularly the strongest ones, were mediated by species richness, highlighting how variation in functional diversity largely stems from changes in the number of frugivorous species foraging on plants. Our results underscore the importance of moving beyond taxonomic metrics to understand diversity interaction patterns, providing insights into habitat management and restoration, and advancing our understanding of how the diversity of frugivore traits influences frugivory and seed dispersal of plant individuals.