Low Abundance of Regular Pollinators and Indirect Competitive Effects of Dominant Small Bees Negatively Affect Passion Fruit Pollination in Smallholder Croplands

Abstract

Land-use changes have led to natural habitat loss and fragmentation, favoring the occurrence of dominant bee species in agroecosystems. This has raised concerns on the dominance effects in pollination-dependent crops like passion fruits (Passiflora edulis Sims) in tropical regions. That is because dominant bee species might overlap their foraging time with regular pollinators, potentially impairing crop yield. Our aim was to understand how dominant small bees affect regular pollinators of passion fruit flowers and its implications on crop production for smallholder farmers. We sampled bees on farms cropping yellow passion fruits in the Cerrado, the Brazilian savanna, and established pollination exclusion experiments to evaluate the interacting effects of dominance and bee community composition on crop yield. We observed a low frequency of regular pollinators, while dominant floral visitors were highly abundant. Dominant pollinators highly overlapped their foraging activity with regular pollinators through time. Contrary to our expectations, the dominance of native and non-native bee species did not directly affect the occurrence of regular pollinators nor crop yield. However, we found evidence that exploitative competition may indirectly affect pollination by regular pollinators. Manual and bee pollination combined increased fruit quality, highlighting the potential benefits of diverse pollinator communities for sustainable crop production. Our findings emphasize the need for strategies that can improve the quality and abundance of resources in agroecosystems for regular native pollinators to optimize pollination in passion fruits on smallholder farms and reduce dominance effects caused by small floral-visiting bees.

Keywords: Apis mellifera; Bumblebee; Carpenter bees; Cerrado; Dominance effects; Ecosystem services.