Providing "corridors" that link patches of undisturbed habitats can help protect species from extinction--at least in the tiny world of spiders and mites that dwell on moss-covered boulders. The find, reported in today's Science, helps to explain some long-held theories in ecology and may help conservationists better assess and mitigate the effects of habitat destruction.
Ecologists have often noticed that species that are abundant in a given area--sparrows, for example--often tend to be spread out across wider geographic regions as well. One explanation is what's called the "rescue effect," which holds that common species are more likely to pioneer new habitats. Andrew Gonzalez of the National Environment Research Council Centre for Population Biology in Berkshire, U.K., and his colleagues wanted to test whether limiting immigration would cause restricted populations to decline or even go extinct.
The team tested their ideas on the miniature ecosystems of moss-covered boulders. They scraped moss away from the rock to leave 20-square-centimeter islands, marooning the inhabitants--tiny spiders, mites, and springtails that would have difficulty surviving on bare rock. A year later, they counted the critters in fragmented sections and in a control section--a 50-square-centimeter patch of undisturbed moss. They tallied 40% fewer species in the fragments. In a second experiment, the scientists left narrow corridors between one set of patches while completely isolating another set. After 6 months, 41% of the species in the isolated fragments had gone extinct, compared to only 14.5% of species in the connected fragments.
There are lessons here for larger ecosystems, Gonzales says. "Clearly movement is important for the long-term existence of any population," he says. "When you start reconnecting [habitats], things don't look so bad and extinction slows down." Ecologist Robert Holt of the University of Kansas praises the study. "These lilliputian landscapes are perfect," he says. "This is an intermediate way station between lab microcosms and the real-world systems that ultimately we're trying to grapple with."