[Pollinator] Shade-Coffee Farms Support Native Bees That Maintain Genetic Diversity in Tropical Forests

[Scott Black]

Shade-Coffee Farms Support Native Bees That 
Maintain Genetic Diversity in Tropical Forests

http://www.sciencedaily.com/releases/2010/07/100726170834.htm

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.

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 Proceedings of 
the National Academy of Sciences.

"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."

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.

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.

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.

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.

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.

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.

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.

"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.

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.

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.

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.

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.

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.

The project was supported by the Helen Olson 
Brower Fellowship at the University of Michigan 
and by the National Science Foundation.




*************************
Scott Hoffman Black
Ecologist/Entomologist
Executive Director
The Xerces Society for Invertebrate Conservation
4828 SE Hawthorne
Portland, OR 97215
Direct line (503) 449-3792
sblack at xerces.org

The Xerces Society is an international, nonprofit 
organization that protects wildlife through the 
conservation of invertebrates and their habitat.

To join the Society, make a contribution, or read about our work,
please visit <http://www.xerces.org/>www.xerces.org.


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