Strips of conserved habitat are turning out to be major wildlife conservation tools; will they be enough?
Imagine the shock last year during a scientific conference at the London Zoo when new maps revealed that once-vast tiger habitat had shrunk dramatically. Although there had been some concern that Project Tiger--a program launched by India in 1973 to conserve the big predator--was not working, the plan still seemed sound. After all, the biologists who designed the plan had been so con- fident of success that the tiger had become India's national symbol, and Prime Minister Indira Gandhi had become patron of the program.
The strategy was simple. The tiger was designated a protected species, and forest reserves were created for the species in which commercial activity was restricted and from which human residents were removed. These protected areas were to serve as refuges where tigers could live and breed without inter- ference. It was assumed that surplus animals would then spill into the sur- rounding forests and move freely between the reserves.
But on the new maps, which were based on satellite data, the reserves appear as starkly isolated patches of forest in a sea of land developed to support a growing human population. "You can't hide from the satellite," says John Seidensticker, a curator of mammals with the Smithsonian Institution and chairman of the Save the Tiger Fund. "It's all out in the open." The main hope now for the species, he maintains, lies between the reserves--in the preserva- tion or creation of corridors connecting the remaining fragments of habitat. In coming to that conclusion, he has had plenty of company. Conservation biologists worldwide are faced with rapid fragmentation of habitat for species ranging from koalas in Australia, to elephants in Asia, to grizzlies in North America. Everywhere, it seems, scientists are wrestling with the conservation answer of the wildlife corridor, usually thought of as a linear stretch of habitat connecting two much larger patches.
In Costa Rica, for example, a habitat corridor now links the Braulio Carrillo National Park to rain forest surrounding La Selva Biological Station. The land drops from an altitude of nearly 3,000 meters (almost 10,000 ft.) to sea level. Among the wildlife in the diverse habitat are more than 400 species of birds, jaguars, howler monkeys, vipers, sloths and thousands of species of insects. Already there are plans to add links to patches of privately owned rain forest. And the whole area eventually may connect with the The Way of the Panther Project--a scheme to link wildlife reserves from Mexico to Colombia.
Other cases abound. In Australia, one of many examples is the country's "coas- tal ribbon," which features prime habitat for koalas and other marsupials. Koalas in particular have specific needs; for the most part they consume only the leaves of a handful of the 650 native species of eucalyptus trees. As new homes sprout along the coast, conservationists are working to preserve cor- ridors for the animals between critical patches of habitat.
The ideas behind wildlife corridors started 30 years ago, with research on islands by two ecologists, the late Robert MacArthur of Princeton and Edward O. Wilson of Harvard. They developed a theory to explain that the bigger an island and the closer it is to mainland that can supply wildlife, the more species it contains. Ecologists then noted that unlike islands in water, habitat "islands" in a landscape can be connected by strips of like habitat. They found ready examples in fencerows used by small mammals such as chip- munks, deer mice and voles to travel between woodlots. River valleys serve as flyways for many birds, and vegetation along riverbanks can connect patches of forest.
Such corridors, argued Wilson and colleague Edwin Willis in 1975, make it easier for animals to colonize patches of habitat--and hence to boost the num- ber …