Thursday, August 6, 2009 - 1:30 PM

COS 105-1: Shade coffee, it’s not just for the birds: Pollen-mediated gene flow for a buzz-pollinated tree

Shalene Jha and Christopher W. Dick. University of Michigan


As the second most valuable commodity in the world, coffee covers more than 11 million ha of land, most of which is in the world’s richest centers of terrestrial biodiversity.  In the neotropics, coffee is traditionally ‘shade-grown’ under a diverse canopy of overstory trees, a habitat which supports native pollinators responsible for improving coffee bush yield. Though shade-grown coffee has garnered interest for serving as potential habitat for native fauna, little is known about how these animals function as pollen dispersers of remnant trees within shade coffee plantations. Long distance pollen dispersal has been documented for tropical trees in fragmented habitats; however, past studies have primarily examined plant species with generalized pollination systems.  Unlike generalized reproductive systems, which can be pollinated by a diverse group of animals, including exotic honeybees, plant species with specialized pollination systems may experience disrupted gene flow in altered habitats if native pollinators are lost.  


We used microsatellite markers to analyze gene flow patterns for Miconia affinis (Melastomataceae), a reproductively specialized understory tree which can only be effectively pollinated by native buzz-pollinating bees.  The 1200 ha study region contains both shade coffee and forest habitats, and is inhabited by 445 adult M. affinis individuals.  Based on paternity analyses, we record numerous long-distance pollen dispersal events, many reaching beyond 1500m.  Pollen dispersal distances are significantly greater than nearest neighbor distances, averaging 279.5m (± 59.3m) for mother trees in forest habitats and 589.2m (± 90.6m) for mother trees in the coffee habitats. Pollen dispersal is also extensive between coffee and forest habitats, with more than 43% of all pollen dispersal events taking place between habitat types.  Such extensive cross-habitat pollen dispersal provides strong evidence that shade-grown coffee farms serve as habitat corridors for native bees and support crucial gene-flow processes for native trees in fragmented landscapes.