The Kenyan hippo. Population dynamics, impacts on riparian vegetation and conflicts with humans

PhD ceremony: Mr. E.M. Kanga, 14.30 uur, Aula Academiegebouw, Broerstraat 5, Groningen

Dissertation: The Kenyan hippo. Population dynamics, impacts on riparian vegetation and conflicts with humans

Promotor(s): prof. H. Olff

Faculty: Mathematics and Natural Sciences

The common hippopotamus, commonly referred to as hippo, is adapted to aquatic habitats, but nocturnally graze on mainland. Despite its vulnerable status, grazing impacts on riparian habitats and rising conflicts with people, the hippo has not been well studied or monitored in many parts of its range, including Kenya. Consequently, the prime aim of the thesis of Erustus Mutembei Kanga was to analyze (1) human-hippo conflicts in Kenya over the 12-year period covering 1997-2008, (2) hippo population dynamics in the Mara region of Kenya during 1958-2006 and (3) the patterns and consequences of hippo and livestock grazing in the riparian-edge habitats of the Mara on vegetation structure, species richness and composition and herbivore abundance and diversity. Kangas results established that human-hippo conflicts increased 26-fold Kenya-wide during 1997-2008. This dramatic rise in human-hippo conflicts is a consequence of both natural and human-mediated disturbances on hippo habitats. Further, his results established that the population of hippos in Mara increased five-fold between 1970 and 2006, despite deteriorating environmental conditions. Lastly the results of Kanga established that the effects of hippos on vegetation structure, species composition and richness, clearly points to a keystone role for hippos. These results confirm that hippos affect a number of ecosystem-level functions and that their influence on other herbivores may be much more important than has been appreciated previously. Kanga suggests that hippo provide some unique ecosystem engineering functions not duplicated by mesoherbivores along riparian-edge habitats. Consequently, any significant decline of hippopotamus populations in the Serengeti-Mara ecosystem and elsewhere in Africa may precipitate considerable erosion of habitat heterogeneity within riparian-edges and the unique biodiversity they support. He recommends urgent steps be taken to alleviate the degradation, fragmentation and loss of hippo habitats in Kenya.