Food Selection by Beavers in Relation to Inducible Defenses of Populus tremuloides

Abstract

Stands of quaking aspen (Populus tremuloides) previously cut by beavers (Castor canadensis) consist mainly of root sprouts exhibiting juvenile morphological characteristics. Feeding experiments showed that beavers avoided these sprouts when normal sprouts and branches were present, and an unidentified compound which has not previously been reported in the Salicaceae appears to be responsible for the deterrence of beaver feeding. High performance liquid chromatography (HPLC) showed that several compounds in aspen bark which act as feeding deterrents to other herbivores were not responsible for beaver deterrence. These compounds were found in higher concentrations in normal aspen sprouts and branches than in juvenile-form sprouts. Since juvenile-form sprouts are clones of mature aspen and arise after beaver cutting occurs, we suggest that quaking aspen is plastic in its defensive chemistry, allocating its resources among various secondary metabolites in response to beaver cutting.