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Wageningen Universiteit Pays Bas (2003)

Multiscale perspectives of species richness in East Africa

Said, M.Y.

Titre : Multiscale perspectives of species richness in East Africa

Auteur : Said, M.Y.

Université de soutenance : Wageningen Universiteit

Grade : PhD thesis 2003

Résumé partiel
This dissertation describes and analyses animal species richness in East Africa from a multi-scale perspective. We studied diversity patterns at sub-continental, national and sub-national level. The study demonstrated that species diversity patterns were scale-dependent. Diversity patterns varied with spatial and temporal scales of observation. Processes and parameters important at one scale were not as relevant at another.

At sub-continental level large herbivore assemblages revealed maximum diversity at intermediate ecosystem productivity. This finding is consistent with other studies on the relation between productivity and species richness. When furthermore comparing climatic and remotely sensed estimates of ecosystem productivity we observed the first to be a better predictor of diversity. Geographical patterns in species richness proved to be very similar among different taxonomic groupings of animal species. Most species groupings showed maximum diversity at intermediate productivity.

At Kenyan national level we analysed the coexistence of pastoralism and wildlife. A study of eighteen arid and semi arid districts revealed that the biomass of human and livestock populations was negatively related to wildlife biomass. An increase in human population density was associated with a significant decline of the density of wildlife populations. This spatio-temporal extension of the ’pastoral road to extinction’ model provided more insights into the antagonistic relation between people, livestock and wildlife. Also it allowed localizing areas of conflict that need specific attention if pastoralism and wildlife are to coexist in harmony.

A further study in the arid zone of Northern Kenya revealed that wildlife distribution was negatively associated with the presence of livestock and water-points. This suggests that livestock oriented interventions in rangelands directly degrade wildlife resources. Further, we demonstrated that the local processes (competition and disturbance) have a direct link to regional patterns. In the north-western, central and coastal areas of Kenya there are signs of local species extinction. The maintenance of regional species pools (be it the neighbouring district or cross border country) are crucial determinants for the persistence of local species assemblages.

Mots clés : biodiversity - synecology - spatial variation - ungulates - wildlife - livestock - pastoralism - vegetation types - kenya

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