Can Codependent Species Survive Forest Breakup?

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The pair found that fewer birds were available to eat the tree's bright red, waxy fruit and disperse its seeds in smaller patches of forest.

Three of the tree's four most common fruit-eating visitors—the striped-cheek greenbul (Andropadus milanjensis), Shelley's greenbul (Andropadus masukuensis), and the green-headed oriole (Oriolus chlorocephalus)—removed 62 to 75 percent less fruit from the trees than in the continuous forest patch. A fourth species, the olive thrush (Turdus olivaceus), was totally absent in small forest patches.

Trees in isolated patches were lucky to disperse as few as a quarter of the seeds that their relatives in the continuous forest were able to spread. These forest fragment trees were more likely to have dense clumps of seedlings growing near the parent tree.

Cordeiro noted that Leptonychia isn't even designated as an endangered species. "If this is happening to a tree common in the landscape, what could be happening to much rarer trees?" he said.

The idea that fragmentation could break up critical partnerships between species "has been floating around for a good while," commented Daniel Simberloff, an ecologist at the University of Tennessee in Knoxville. But, until now, there has been no direct evidence, he said.

"Seeds of this tree are dispersed by a number of non-specialist dispersers, not by one species that seeks out this tree," said Simberloff. "Thus, this is a species that might have been less expected to suffer from fragmentation than many others, since there will always be some possible seed-dispersing species around."

Trees dependent on a single animal species for seed dispersal could be at even greater risk of extinction, he said.

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