Pollinator Diversity and Pollen Flow of an Emergent Tropical Tree Species in a Fragmented Forest

Abstract

In fragmented landscapes, pollination is key for connectivity within and between plant populations, improving fecundity and genetic diversity. Pollination research has largely focused on crops and understory plants, while trees, the key components of tropical forests, have received much less attention. In this study, we used colored sticky traps to investigate the pollination biology of a large-seeded tree, Antiaris toxicaria Lesch. (Moraceae), across six forest fragments within a 10-km radius in Xishuangbanna, southwest China. We explored how forest fragmentation shapes pollinator assemblages and potential pollen mass flow patterns, and how these patterns varied across different pollinator groups. We collected 1137 morphospecies that were confirmed to carry pollen grains of A. toxicaria. Dipterans and hymenopterans were the most species-rich and carried the greatest number of pollen grains. Pollinator richness and abundance showed hump-shaped relationships with fragment size, potentially due to edge effects in the medium-sized fragments and dilution effects in the largest fragments. In contrast, pollen mass flow increased with increasing fragment size, except in the smallest fragment, where we found a substantial increase likely due to the high density of focal trees. These results suggest that habitat fragmentation only negatively impacted potential pollination processes in small fragments through reduced pollinator diversity. Protecting and improving connectivity among medium to large fragments may help sustain pollination processes in fragmented landscapes. Future research on pollinator behavior and whether pollen is successfully dispersed among fragments would provide additional insights as to whether the populations of large-seeded plants retain viability in small to medium-sized fragments.