Environment‐dependent influence of fruit size upon the distribution of the Malesian archipelagic flora

Societal Impact Statement We found evidence that larger fruited plant species are more likely to be found in aseasonal wet areas of Malesia. These areas are likely to be impacted by increasing human encroachment, which threatens both large‐fruited species and the large fauna that are most likely responsible for their dispersal. This synergistic threat could drive the loss of fruit‐crop relatives that potentially have key traits for resilient fruit crops of the future. Summary It is unclear how fruit size determines distributions of megadiverse tropical flora. Energetic constraints of ecosystems suggest plant species with larger fruit should be found in the higher productivity, aseasonal wet tropics. However, the probability of seed dispersal over large scales should be increased by fruits being smaller, due to being available to a greater number of dispersal agents. We use a Bayesian phylogenetic model of species occurrence for >3400 species in Malesia to test how fruit size and environment interact to determine species distributions across the archipelago. We show that larger fruited species are more likely to occur in aseasonal wet areas. We also found that smaller fruit size was associated with species occurrence in more mountainous areas. Fruit size interacts with environmental variables to shape plant distributions across the megadiverse Malesian islands. The evolutionary processes that influence the patterns we have observed require further examination.