Vertebrate frugivore loss: High-risk geographic areas and hypothesized community-level impacts
Animal-mediated seed dispersal may enable seeds to escape from predators, parasites, and competitors. It can also boost germination by directing seeds to favorable germination sites and, for some species, removing germination inhibitors. A growing amount of empirical research has found quantifiable decreases in plant recruitment as a result of seed disperser losses. Such decreases have the potential to affect broad plant community dynamics. However, these community effects are little understood. Furthermore, the prevalence of seed dispersal disruption (i.e., its frequency of occurrence and the number of species affected) is unknown. I used a database of known vertebrate seed dispersers, in conjunction with published seed dispersal networks, to identify geographic areas at particular risk of seed dispersal disruption and to assess the proportion of angiosperms potentially affected in each region.
Predicted percentages of angiosperm species affected are particularly high in tropical and southern hemisphere regions (2-14%), as well as on oceanic islands (12%). In cases of seed dispersal disruption, hypothesized community-level effects include reduced regional plant cover, reduced alpha-scale plant diversity, and increased erosion and altered hydrology. These effects could facilitate invasion by wind-dispersed non-native species. Adequate testing and refinement of these hypotheses are hindered by the mathematical complexity of integrating multiple species with varied life histories; limited resources for long-term empirical studies; and the long generation times that are typical of fleshy-fruited plant species and create delayed community-level responses to seed disperser losses. To better understand these relationships, it is critical that new experimental and theoretical methods be developed. Collaborations across both ecological subdisciplines and geographic regions may help elucidate complex patterns.