An experimental test of frequency-dependent food selection: winter browsing by moose

Penned moose Alces alces (L.) offered birch and rowan trees in various proportions in experimental tests showed a clear preference for birch both in terms of selection and use of trees. Both tree selection and tree use was frequency-independent, i.e. the preference for birches did not vary with either the number of birches, or total birch biomass available. The preference for birch was not absolute, i.e. rowans were also present in the diet. Birch were more profitable than rowans in terms of biomass intake rate, whereas rowans were more “nutritious” than birches. The results are consistent with both the optimal diet theory and the “nutrient mixture” hypothesis, although neither of the hypotheses are unambiguous regarding frequency-dependent food selection. It is argued, however, that tree selection and use by moose rather should be considered as a patch use problem and that trees should not be regarded as particulate food items as in most foraging models.