SLU/Dept. of Wildlife, Fish and Environmental Studies
Abstract
Invasive plants, growing and spreading outside of their native range, can severely modify ecosystems. Herbivory has often been seen as a potential control of invasions, but has rarely been considered as a potential impacted trophic level. Considering the habitat selection by large herbivore being a reflection of their feeding habits and predator avoidance, I studied the impact of the invasive Chromolaena odorata on African large herbivores in Hluhluwe-iMfolozi Park, KwaZulu-Natal, South Africa. This plant is not eaten by the animals but affects the diversity of the grass species, the height and cover of woody species and can create high and thick walls as a barrier for most animals. Abundance of 14 species of herbivores was estimated by dung counting, and the presence and density of the invasive shrub was estimated every 5 meters on 24 transects in the park in 2004 (high density of invasive) and 2014 (low density of invasive). This data was used to understand a predictive habitat selection analysis (Resource Selection Functions) and to analyse the recolonization of previously invaded patches based on the change of dung abundance. A Principal Component Analysis showed that closed woody habitats are the most invaded. The results are a mirror of the high heterogeneity of habitats and herbivores in African savannas. Grazers (buffalo, zebra, warthog, and wildebeest) as well as browsers (nyala) avoided high density patches that are a physical barrier to selection. Grazers seem also to avoid less dense patches where food availability might be diminished and where ambush predators could hide. However, bushpigs select invaded patches, which may be used as a shelter against predators for example. Other species appear to ignore the invasion; because their home area does not overlap the invaded area (impala) or because the invasion does not affect them (elephant)
