Tropical Forest Fragments Enhance Pollinator Activity in Nearby Coffee Crops

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Abstract
Abstract: Crop pollination by wild bees is an ecosystem service of enormous value, but it is under increasing threat from agricultural intensification. As with many ecosystem services, the mechanisms, scales, and species through which crop pollination is provided are too poorly understood to inform land‐use decisions. I investigated the role of tropical forest remnants as sources of pollinators to surrounding coffee crops in Costa Rica. In 2001 and 2002 I observed bee activity and pollen deposition rates at coffee flowers along distance gradients from two fragments and one narrow riparian strip of forest. Eleven eusocial species were the most common visitors: 10 species of native meliponines and the introduced honeybee,Apis mellifera(hereafterApis). Bee richness, overall visitation rate, and pollen deposition rate were all significantly higher in sites within approximately 100 m of forest fragments than in sites farther away (maximum distance of 1.6 km).Apisvisitation rates were constant across the distance gradient, however, andApisaccounted for >90% of all floral visits in distant sites. The gradient from the riparian strip showed a similar drop in bee species richness with distance, but visitation rates were uniformly low along the gradient. Throughout the study area,Apisabundances declined sharply from 2001 to 2002, reducing visitation rates by over 50% in distant sites (whereApiswas almost the only pollinator). In near sites, however, overall visitation rates dropped only 9% because native species almost entirely compensated for theApisdecline. Forest fragments (more so than the riparian strip) thus provided nearby coffee with a diversity of bees that increased both the amount and stability of pollination services by reducing dependence on a single introduced pollinator. Exploring the economic links between forest preservation and coffee cultivation may help align the goals of conservation and agriculture within many regions of global conservation priority.