Many vulnerable species are facing reduced numbers because the adaptations that have served them for thousands of years make them unable to survive small changes in temperature or precipitation. When faced with climate change and other threats to their habitat, some species may not be able to relocate quickly enough to save them from extinction. A new technique called assisted colonization may prove to be an innovative solution.

Unnnatural Barricades and Fragmented Habitats
Human activities have barred many species from migrating on their own. The Quino checkerspot butterfly, indigenous to California and Mexico, has declined rapidly and is now listed as an endangered species. A major driver of the Quino's decline has been its inability to shift its range, due mainly to the many changes humans have wrought on the landscape. Indeed, unnatural barriers – roads, parking lots, houses, etc. – have blocked many species' natural migratory ability. These species have essentially been "barricaded in" by human activities on the surface of the Earth.

Even policies explicitly meant to preserve wildlife can restrict and fragment habitats. National parks serve as refuges for untold numbers of species. Inside parks, animals are free from hunting, development, and other threats to their habitat. In a changing climate, though, migration may be the only way that these species can ensure their longer-term survival. Yet once they leave the safety of protected areas, they become susceptible to hunting and may face unnatural barriers. Ironically, as the climate changes, the park system meant to protect these animals has begun to fragment their habitats and have created obstacles to safe migration.

A New Conservation Approach
The impacts of climate change on ecosystems are occurring sooner and more rapidly than often predicted. Traditional conservation techniques may not be up to this unprecedented challenge. A new report published in the journal Science champions "assisted colonization"--small, controlled introductions of well-understood species between similar ecosystem regions--as one possible solution.

The article's seven co-authors note that while such a strategy "flies in the face of conventional conservation approaches," it may be the only way to ensure the survival of many species. They argue that ecologists and biologists today have a greater understanding of species' range and habitat requirements, and can make informed, low-risk relocations.

Only some species are candidates for assisted colonization, and in the authors' decision framework, only species at a very high risk of extinction are suitable. Species at little or moderate risk could be conserved through other practices, like connecting current to future potential habitats. In particular, species that have differentiated populations are ideal candidates for assisted colonization. For instance, certain populations of staghorn coral have adapted to the warmer waters at lower latitudes. Already, as historically colder waters have warmed, higher-latitude staghorn coral populations with low heat tolerances have failed. Transplanting heat-tolerant populations into higher latitudes may help to preserve the species as the climate changes.

Potential Dangers

Conservationists generally balk at any kind of human intervention in natural ecosystems, as many such projects have had negative and even disastrous consequences in the past. For instance, cane toads were deliberately introduced onto the continent of Australia to control agricultural pests; today, in the absence of natural predators, toads reproduce at alarming rates and are displacing indigenous species.

The cane toad (Bufo marinus) invasion from 1945 to 1980 in five-year intervals.
Source: Wikimedia Commons

No assisted colonization will be without its risk. The drastic transfer of the cane toad from the American tropics to the arid Australian continent resulted in an equally drastic population explosion. The authors of the Science study insist that the potential risks of such a scheme may be outweighed by the potential benefits, especially given the high likelihood of continued global warming. The prospects of many species are so bleak as to make assisted colonization their best—or only—hope.

RELATED LINKS:

Government of Australia – The feral cane toad (Bufo marinus) fact sheet

Scientific American: "Deporting Plants and Animals to Protect Them from Climate Change"

EARTHTRENDS DATA:

Theme: Biodiversity and Protected Areas