Megafruit and megafauna diversity are positively associated, while megafruit traits are related to abiotic factors, in tropical Asia

Aim: For tens of millions of years, herbivorous megafauna were abundant across the globe, fulfilling important ecological roles including seed dispersal. Megafruits are very large fruits that are dispersed most effectively by megafauna. However, megafruits also occur in ecosystems where megafauna are extinct or were never present, emphasizing our incomplete understanding of megafauna–megafruit relationships. Here we use the complex biogeography of tropical Asia to investigate how megafruit diversity and traits are associated with the diversity of megafauna, smaller animals, and abiotic factors. Location: Tropical Asia, from the Indian subcontinent in the west to tropical China in the north to the Maluku archipelago (Indonesia) in the east. Time period: Late Pleistocene to the present day. Major taxa studied: Megafauna (body weight > 500 kg) that consume fruits, including stegodons, elephants, rhinoceroses, giant tapirs, and large bovids. Fleshy-fruited plant species across the region with a fruit width > 40 mm (i.e., megafruits). Methods: We compiled a list of all megafruits along with selected plant, fruit, and seed traits in 16 subregions across tropical Asia. We explored biogeographical patterns in megafruit diversity and traits in relation to the diversities of past and present megafauna, large- and medium-sized animals and abiotic factors (mean temperature, mean precipitation, precipitation seasonality, insularity). Results: We identified 496 megafruits in tropical Asia. Megafruit diversity was highest in subregions with high megafaunal diversity, particularly extant species. Megafruit traits were influenced most strongly by abiotic factors (mainly temperature and land area), and weakly by megafauna and smaller dispersers. Main conclusions: Our results are consistent with megafauna maintaining or responding to megafruit diversity, but variation in megafruit traits is primarily associated with abiotic factors. Given the massive megafaunal losses in tropical Asia since the Late Pleistocene, it is important to identify fruit traits that can increase megafauna-dependence and thus vulnerability to these losses.