he above diagram depicts part of the food web of the Canadian boreal forest (after Stenseth et al., 1998). Essentially there are three trophic levels. During the summer, various herbs and grasses support a community of herbivores dominated (65%-80% total herbivore biomass) by the snowshoe hare (Lepus americanus). During the winter, some of the herbivores hibernate, while others, including the hare, remain active. The latter species depends on woody browse and is itself a principal source of nutrition for many species. The top trophic level is comprised of mammalian and avian predators which differ both with regard to mobility and their dependence on the hare.