Tropical Seed Dispersal Networks: Emerging Patterns, Biases, and Keystone Species Traits

Abstract

Seed dispersal mediated by animals is a pivotal ecological interaction in the tropics. Despite a long tradition of tropical seed dispersal studies, only recently the drivers of the structure of seed dispersal networks are beginning to be uncovered at macroecological scales. The knowledge on tropical seed dispersal comes mainly from avian dispersal studies in the Neotropics while other frugivores and tropical regions are strongly understudied. The networks sampled with a combination of visitation census and seed recovery from feces seem more reliable of the number of detected links and web asymmetry than networks based on a single method. Our review reveals that keystone species in most networks share a set of functional traits likely influenced by species phylogeny. Woody plants bearing small berries (in the Melastomataceae, Myrtaceae, Moraceae, and Urticaceae families) were the most frequent keystone plants whereas two groups of keystone animals could be identified, namely: small obligate frugivores (Pipridae and Thraupidae) and large animals including a variety of taxonomic groups such as cracids, rodents, monkeys, and megafauna. Large keystone species tend to face a higher extinction risk leading to a concern on the sustainability of the dispersal services they provide, mainly to large-seeded plant species that are essential to ecosystem functioning.