VEGETATION AND HABITAT USE AMONG LARGE HERBIVORES IN KIMANA WILDLIFE SANCTUARY, AMBOSELI ECOSYSTEM, KENYA

Abstract

Understanding the composition and structure of vegetation is important in conservation and management of large herbivores worldwide. The aim of the study was to obtain information on the composition and structure of vegetation and habitat use among large herbivores in Kimana Wildlife Sanctuary (KWS), Amboseli ecosystem, Kenya. The objectives of the study were to characterize and to classify vegetation in KWS, to determine the structure and composition of vegetation in KWS, to determine the population density of large herbivores in KWS and to determine the seasonal variations in habitat selectivity, niche breadth and habitat overlap indices among large herbivores in KWS. Five vegetation types were classified and mapped using remote sensing but seven vegetation types were further classified using physiognomic features and dominant species. Data on vegetation and large herbivore were collected between May, 2012 and December, 2012 during both the dry and wet seasons using Stratified Research Design. Random and systematic sampling methods were used for sampling vegetation using Point–Centered Quarter method, Belt transect method, Descending Step Point method and Pasture Disc Meter method while random sampling method was used in large herbivore size determination. Variations were observed across vegetation types in woody species richness, diversity, evenness, similarity and Importance Value Index (IVI). Frequency of woody plant stems (dbh≥5cm) showed an inverted J-shaped structure in Acacia tortilis woodland, wooded grassland and sparse shrubland but a J-shaped structure in Acacia xanthophloea woodland. Frequencies of grass ecological categories differed significantly in all the vegetation types, with the exception of open grassland. Increaser II grass species; C. dactylon, S. fimbriatus and H. schimperii dominated in all the vegetation types, with the exception of wooded grassland, which was dominated by P. stramineum, an increaser I grass species. Grass standing crop biomass, grass basal cover, grass height and inter-tuft distance also varied across vegetation types. A total of 3,983 individuals of large herbivores were counted, 2,153 in the dry season and 1,830 in the wet season. Large herbivore overall density was 1.980 ± 0.236 and 1.803 ± 0.2156 during the dry and the wet seasons respectively. Plains zebras (Equus quagga Boddaert) were the densest species during the dry, 6.793 ± 0.871 and the wet season, 6.473 ± 0.848 and Cape elands significantly increased their population densities during the wet season. Larger herbivores showed greater selection for wooded grassland during the dry (≈71%) and the wet (≈85%) seasons. Niche breadth indices were low among the large herbivores during the dry (≈73%) and the wet (≈87%) seasons. Habitat overlap indices were high among the large herbivores during the dry (≈67%) and the wet (≈51%) seasons. In conclusion, the structure and composition of vegetation varied across and within vegetation types, cape elands significantly increased their population densities during the wet season and the large herbivores were highly selective able to specialize on a few habitat types, hence, they greatly overlapped in habitat use.