Forest fragmentation and loss reduce richness, availability, and specialization in tropical hummingbird communities

Hummingbirdsare important pollinators of many native Neotropical plants but their abundance and diversity in landscapes dominated by intensive human uses such as agriculture have rarely been examined, despite such land-uses prevailing in the tropics. We examined how tropical deforestationaffects hummingbirdcommunity structure in premontane forest patches embedded in a tropical countryside of Coto Brus Canton, Costa Rica. We captured hummingbirdsin fourteen landscapes representing a gradient in patch size and forest amount, and tested for the effects of these variables on (1) hummingbirdcaptures at flowers (pollinator availability); (2) species richness; and (3) filtering of functional traits. After accounting for sampling effects, both hummingbirdavailability and species richness declined by 40% and 50%, respectively, across the gradient in deforestationthat we observed (9–66% forest within 1000 m). Focal patch size was the strongest predictor, even after statistically accounting for the amount of forest and matrix composition of landscapes. These reductions in availability and richness were well predicted by functional traits; morphologically specialized species with the capacity to transport long-distance outcrossedpollen and low functional redundancy within the pollinator network showed the greatest sensitivity to landscape change. We hypothesize that declines in hummingbirdavailability, diversity, and functional traits are important mechanisms driving the observed pollen limitation of ornithophilous flowers in fragmented tropical landscapes. Efforts to conserve large forest patches and enhance matrix permeability are critical for maintaining forest hummingbirdcommunities and pollination services under current and predicted deforestationregimes.