Most eastern North American reserves too small

As reserves become isolated by development, animals can die out in part because they can no longer move between populations. Because smaller isolated reserves are more likely to lose species, the question is how small is too small? New research suggests that most reserves in eastern North America are too small.

"Species may not be safe from the effects of encroaching development, even in reserves created for their protection," says Brent Gurd, who did this work at the University of Guelph in Ontario, Canada, and is now at Simon Fraser University in Burnaby, British Columbia. Gurd and his co- authors present this work in the October issue of Conservation Biology.

Some eastern North American reserves have already lost species since European settlement: previous research has shown that there are fewer terrestrial mammals in seven of 10 reserves in extensively developed parts of Canada. Some of these reserves have lost as many as 10 species. The reserves studied were in the Alleghenian-Illinoian mammal province, which encompasses the northeast quadrant of the U.S. and adjacent slivers of Canada.

If future development isolates other reserves in this mammal province, they could also lose species. To estimate the smallest size these reserves could be without losing species, Gurd and his colleagues compared the historical and current numbers of species in 10 reserves in the mammal province. The researchers then compared this minimum size to that of 2355 reserves and reserve assemblages that accounted for about 10% of the mammal province.

Gurd and his colleagues estimated that the minimum size for reserves in the province should be roughly 1,000 square miles. However, hardly any of the reserves considered met this minimum size -- only 14 of the 2355 were 1,000 square miles or larger. The researchers caution that this estimate is conservative and that reserves may actually need to be even larger.

"Few reserves appear large enough to avoid loss of some mammal species without the additional cost of active management of habitat or populations," say the researchers. For instance, they have found that wolves have not persisted in reserves smaller than 370 square miles.

Gurd and his colleagues recommend combining small reserves into assemblages of at least 1,000 square miles by establishing immigration corridors and buffer zones.

Gurd's co-authors are: Thomas Nudds of the University of Guelph in Ontario, Canada, and Don Rivard of Parks Canada in Hull, Quebec.

For faxes of papers, contact Robin Meadows robin@nasw.org

For more information about the Society for Conservation Biology: http://conbio.net/scb/

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