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Biogeographic Evidence for the Evolution of Chemical Defense by Boreal Birch and Willow Against Mammalian Browsing

John P. Bryant, Jorma Tahvanainen, Matti Sulkinoja, Riitta Julkunen-Tiitto, Paul Reichardt and Terry Green
The American Naturalist
Vol. 134, No. 1 (Jul., 1989), pp. 20-34
Stable URL: http://www.jstor.org/stable/2462273
Page Count: 15
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Biogeographic Evidence for the Evolution of Chemical Defense by Boreal Birch and Willow Against Mammalian Browsing
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Abstract

Experiments have demonstrated that winter-dormant boreal woody plants, in particular the juvenile phase of these plants, contain secondary metabolites that deter browsing by mammals such as hares. However, this evidence does not directly indicate that these substances are the result of defensive evolution by boreal trees and shrubs. In this paper we have provided experimental evidence that winter browsing by mammals, especially hares, has selected boreal woody plants for chemical defense and that the 10-yr hare cycle has influenced woody-plant defensive evolution in boreal forests. Our results further indicate that Alaskan snowshoe hares have evolved more-effective methods of detoxification of birch and willow chemical defenses than have Finnish mountain hares. Thus, we suggest that chemical coevolution has occurred between boreal woody plants and boreal hares and that this process has been influenced by the 10-yr hare cycle.

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