Nature reserves too small to protect species

New research suggests that most reserves in eastern North America are too small to hold onto the mammal species they have sometimes been created to protect.

“Species may not be safe from the effects of encroaching development, even in reserves created for their protection,” commented Brent Gurd, one of the researchers involved in the University of Guelph, Ontario, project, which appears in October’s issue of Conservation Biology, published by the Society for Conservation Biology. The study conducted in the Alleghenian-Illinoian mammal province, which encompasses the northeast quadrant of the US and adjacent slivers of Canada found that there are fewer terrestrial mammals in seven of 10 reserves in extensively developed parts of Canada, some of which have lost as many as 10 species.

If future development isolates other reserves in this mammal province, they could also lose further species, the researchers believe, with animals no longer being able to move between populations to mate. 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 2,355 reserves and reserve assemblages that accounted for about 10% of the mammal province.

The estimated minimum required size for reserves in the province is roughly 1,000 square miles, the researchers believe, although they warn that this estimate is conservative and that reserves may actually need to be even larger. However, hardly any of the reserves considered met this minimum size – only 14 of the 2,355 were 1,000 square miles or 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.

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