deer eliminate bears (!)

September 21, 2005

in Environmental issues, Science

Here’s a startling update to the deer overpopulation thread.  A paper in the latest issue of Conservation Biology described how Black Bears (Ursus americanus) have been extirpated from an island in the Gulf of St. Lawrence by the introduction of White-tailed Deer.

Anticosti Island, Quebec is a large (7943 sq km/3000+ sq mi) island that once supported an abundant population of bears, but no deer.  About 220 deer were introduced on the island in 1896, and by the early 1930s numbers had reached greater than 50,000; currently there are between 60,000 and 120,000 deer on Anticosti.  By the time the population reached a high density, the deer had severely reduced or even extirpated the deciduous shrubs on the island.

Bears do not digest foliage very efficiently, and must consume large quantities of berries in order to accumulate enough fat to hibernate through the winter.  Berries were once abundant on Anticosti, but a recent survey found an average of only 0.28 berries per square meter.  The deer, which prefer deciduous shrubs to conifers, have overbrowsed all the berry-producing plants.  In particular, shrubs of the Rubus family (raspberries, blackberries) are browsed before they can even reach fruiting height.  Bears need at least 66 berries per square meter to even maintain body mass.  Thus, bears cannot even be re-introduced onto Anticosti, as it is no longer able to support them.

An astounding and sobering example of the effects of deer overpopulation!

Cote, S.D. 2005.  Extirpation of a large black bear population by introduced white-tailed deer. Conservation Biology 19:1668-1671.

Aaron September 24, 2005 at 7:51 pm

Recently I read somewhere that the Whitetail deer population in the United States has expanded to the point where they're pushing a number of native species out of areas that they have historically populated as far back as anybody can remember. Specifically the pronghorn antelope in the West, from the Great Plains on, are being steadily driven westward.

It's been proposed that this phenomenon is a result of the lack of any viable predation provided by large carnivores like wolves. Although Timberwolves have been reintroduced in some places, they're nowhere near the numbers necessary to have any meaningful effect on the Whitetail beer population.

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