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<h1><b>Shade-Coffee Farms Support Native Bees That Maintain Genetic
Diversity in Tropical
Forests</b></h1>
<a href="http://www.sciencedaily.com/releases/2010/07/100726170834.htm" eudora="autourl">
http://www.sciencedaily.com/releases/2010/07/100726170834.htm<br><br>
</a>ScienceDaily (July 27, 2010) Shade-grown coffee farms support
native bees that help maintain the health of some of the world's most
biodiverse tropical regions, according to a study by a University of
Michigan biologist and a colleague at the University of California,
Berkeley.<br><br>
The study suggests that by pollinating native trees on shade-coffee farms
and adjacent patches of forest, the bees help preserve the genetic
diversity of remnant native-tree populations. The study was published
online in the <i>Proceedings of the National Academy of
Sciences</i>.<br><br>
"A concern in tropical agriculture areas is that increasingly
fragmented landscapes isolate native plant populations, eventually
leading to lower genetic diversity," said Christopher Dick, a U-M
assistant professor of ecology and evolutionary biology. "But this
study shows that specialized native bees help enhance the fecundity and
the genetic diversity of remnant native trees, which could serve as
reservoirs for future forest regeneration."<br><br>
An estimated 32.1 million acres of tropical forest are destroyed each
year by the expansion of cropland, pasture and logging. Often grown
adjacent to remnant forest patches, coffee crops cover more than 27
million acres of land in many of the world's most biodiverse
regions.<br><br>
Over the last three decades, many Latin American coffee farmers have
abandoned traditional shade-growing techniques, in which plants are grown
beneath a diverse canopy of trees. In an effort to increase production,
much of the acreage has been converted to "sun coffee," which
involves thinning or removing the canopy.<br><br>
Previous studies have demonstrated that shade-grown farms boost
biodiversity by providing a haven for migratory birds, nonmigratory bats
and other beneficial creatures. Shade-coffee farms also require far less
synthetic fertilizer, pesticides and herbicides than sun-coffee
plantations.<br><br>
In the latest study, U-M's Dick and UC-Berkeley's Shalene Jha
investigated the role of native bees that pollinate native trees in and
around shade-grown coffee farms in the highlands of southern Chiapas,
Mexico. In their study area, tropical forest now represents less than 10
percent of the land cover.<br><br>
Jha and Dick wanted to determine the degree to which native bees, which
forage for pollen and nectar and pollinate trees in the process,
facilitate gene flow between the remnant forest and adjacent shade-coffee
farms.<br><br>
They focused on Miconia affinis, a small, native understory tree that
many farmers allow to invade shade-coffee farms because the trees help
control soil erosion.<br><br>
M. affinis, commonly known as the saquiyac tree, is pollinated by an
unusual method known as buzz pollination. In order to release pollen from
the tree's flowers, bees grab hold and vibrate their flight muscles,
shaking the pollen free. Non-native Africanized honeybees don't perform
buzz pollination, but many native bees do.<br><br>
"Our focus on a buzz-pollinated tree allowed us to exclude
Africanized honeybees and highlight the role of native bees as both
pollinators and vectors of gene flow in the shade-coffee landscape
mosaic," said Jha, a postdoctoral fellow at UC-Berkeley who
conducted the research while earning her doctorate at U-M.<br><br>
Jha and Dick combined field observations with seed-parentage genetic
analysis of Miconia affinis. They found that trees growing on
shade-coffee farms received bee-delivered pollen from twice as many donor
trees as M. affinis trees growing in the adjacent remnant forest. The
higher number of pollen donors translates into greater genetic diversity
among the offspring of the shade-farm trees.<br><br>
Seed parentage analysis revealed that pollen from forest trees sired 65.1
percent of the seeds sampled from M. affinis trees growing in a
shade-coffee habitat. That finding demonstrates that native bees are
promoting gene flow between the remnant forest and the coffee farms --
bridging the two habitat types -- and that the shade-farm trees serve as
a repository of local M. affinis genetic diversity, according to the
authors.<br><br>
In addition, Jha and Dick found that native bees carried pollen twice as
far in a shade-coffee habitat than they did in the forest. They
documented shade-farm pollination trips of nearly a mile, which are among
the longest precisely recorded pollination trips by native tropical
bees.<br><br>
Jha and Dick said their results likely apply to other buzz-pollinated
plants, which represent about 8 percent of the world's flowering plant
species, as well as to other native plants whose limited pollen and
nectar rewards don't attract honeybees.<br><br>
The enhanced genetic diversity of the shade-farm trees could provide a
reservoir for future forest regeneration, as the coffee farms typically
fall out of production in less than a century. Given that potential,
along with the shade farm's previously identified roles in connecting
habitat patches and sheltering native wildlife, it is important to
encourage this traditional style of agriculture, Jha and Dick
said.<br><br>
The project was supported by the Helen Olson Brower Fellowship at the
University of Michigan and by the National Science Foundation.<br><br>
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*************************<br>
Scott Hoffman Black<br>
Ecologist/Entomologist<br>
Executive Director<br>
The Xerces Society for Invertebrate Conservation<br>
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Direct line (503) 449-3792<br>
sblack@xerces.org<br><br>
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