Effects of the availability of herbaceous food on vole attacks on birch seedlings

AbstractAccording to the optimal diet theory, predators should consume low-quality prey only when the availability of better-quality prey is low. The model of short-term apparent competition predicts, somewhat contradictorily, that low-quality prey co-occurring in the same patches with high-quality prey should be attacked more than low-quality prey in patches containing no high-quality prey. The prediction should apply, in particular, to poor environments. We compared vole attacks on experimental birch seedlings (low-quality prey) in patches with and without herbs (high-quality prey) in experimental enclosures with non-depleted or depleted herbaceous vegetation. Voles attacked fewer birch seedlings in the non-depleted enclosures compared to the depleted ones. They attacked more birch seedlings in patches with herbs than in patches without herbs independently of food depletion in the enclosure. Tree-seedling predation increased with vole density, but the increase was more pronounced in the depleted enclosu...