for National Geographic News
On the African island nation of Madagascar, only primates called lemurs are big enough to move the seeds of many trees around and thus improve the chances of the trees' survival.
"Lemurs are very important seed dispersers in Malagasy rainforests," said Chris Birkinshaw, a biologist with the Missouri Botanical Garden in St. Louis who is an expert on lemur seed dispersal.
There are 38 known species of lemurs, which are found on Madagascar only. They range in size from the 2.5-inch (6-centimeter) pygmy mouse lemur (the world's smallest primate) to the indri, which is the size of a small child.
Birkinshaw recently conducted a study in the Lokobe reserve in the northern part of the country. He found that 54 percent of the tree species and 67 percent of individual trees there had grown from seeds dispersed only by the black lemur, a medium-size primate. Lemurs spread the seeds by eating the trees' fruits and expelling the seeds as they defecate.
Lemur populations are dwindling on the 225,000-square-mile (580,000-square-kilometer) island. Conservationists fear that the trees that rely on lemurs will disappear along with the primates.
"[The trees' fruits] are some big foods, and there's nobody around anymore except lemurs and maybe, possibly, [introduced] pigs who can eat these foods and disperse the seeds," said Joerg Ganzhorn, a primatologist at the University of Hamburg in Germany.
Ganzhorn's research in the dry forests of western Madagascar shows that lemurs are important seed dispersers for about 10 percent of the trees there.
The clearing of forests to make way for seasonal crops and provide grazing for cattle are the major threats to Madagascar's forests. But areas that look healthy but contain small lemur populations presumably contain trees without adequate seed dispersal, Birkinshaw said.
"In such forests, wind-dispersed trees or trees dispersed by small birds would have a competitive advantage over lemur-dispersed species, leading perhaps to changes in their relative abundances," he said. "Reintroduction of seed-dispersing lemurs should be considered in such circumstances."
Lemur Seed Dispersal
Lemurs, according to Birkinshaw, are such good seed dispersers because they can swallow big seeds: the cat-size black lemur, for example, can swallow seeds up to 1.6 inches (4 centimeters) long and as many as ten such seeds in one sitting.
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