The savannas of East Africa, perhaps more than anywhere in the world, are known for dramatic plant–animal interactions. Although large herbivores are less common above timberline than below it in East Africa, herbivory is also a powerful force in Afroalpine plant ecology. Many vertebrates and invertebrate herbivore species occur above treeline on Mount Kenya (Moreau 1944; Coe 1967; Jabbal & Harmsen 1968; Coe & Foster 1972; Mulkey et al 1984; Young 1991; Young & Evans 1993). Herbivores influence the distribution of plant species, the size structure of populations, and the success of individual plants on Mount Kenya.
Long-term studies of giant rosette Lobelia and Senecio species have brought to light a number of interesting patterns of herbivory that have major impacts on the biology of these species.
The two high alpine giant rosette lobelias on Mount Kenya are Lobelia telekii and L. keniensis. Mount Kenya lobelias are subject to herbivory from a variety of animal species (Table 18.1). None of the herbivores is host-specific, except perhaps the coleopteran larvae associated with L. telekii roots. Most of these herbivores have only minor effects. However, Lobelia populations near hyrax colonies have suffered severe predation.
The leaves and stems of both Lobelia species are protected by a bitter latex containing anti-herbivore compounds (Mabberley 1975). Although this may limit the activity of their herbivores, it far from renders the plants invulnerable.