Factors influencing population and interspecific interaction of three primates in South Nandi forest, Kenya

Abstract

The distribution of non-human primates in tropical forests is highly influenced by vegetation structure, interspecific interactions and human-induced threats. Reported disturbance in the form of charcoal burning, farming, tree extraction for construction poles or timber, encroachment along the forest boundaries and unplanned infrastructure interferes with the forest edges and interiors, which affect the distribution of primate species. The purpose of this study was to assess the population of the Black and White Colobus (Colobus guereza), Blue Monkey (Cercopithecus mitis) and Red-tailed Monkey (Cercopithecus ascanius) in the forest edge and interior in South Nandi Forest during the dry and wet seasons. Their interspecific interactions as well as effects of factors such as human-induced threats, canopy cover, height of trees and stem density were also assessed. The study adopted an ecological survey design with 7 random line transects being established at both the interior and edge locations. The population densities of Black and White Colobus and Blue Monkey were derived using distance sampling. Observations for the Red-tailed Monkey did not attain the minimum required for distance sampling to be used hence their densities were not estimated. Overall, there was a high density of Blue Monkey (0.88±0.19 animals/ha) as compared to the Black and White Colobus (0.63±0.16 animals/ha). The forest interior had high populations of the Blue Monkey (0.99±0.30 animals/ha) and Black and White Colobus (0.89±0.30 animals/ha) as compared to the forest edge. Primate observations were high during the wet season as compared to the dry season. More observations (78 observations) were made for the Black and White Colobus in the wet season as compared to the Blue Monkey (59 observations) and Red-tailed Monkey (9 observations). Blue Monkey interacted more with both the Black and White Colobus and the Red-tailed Monkey with the level of interaction being high (45%) between the Black and White Colobus and the Blue Monkey. These two species form feeding associations especially during the dry season when food is scarce. Major trees utilized included Prunus africana and Croton megalocarpus. Even though the highest averages for stem density (Mean= 56.2), height (Mean= 20.3) and canopy cover (Mean= 64.0) were recorded in the forest interior, independent samples t-test showed there was no significant difference (p>0.05) of these factors in the forest edge and interior. Awareness raising among the locals through the Community Forest Associations should be carried out to sensitize them on impacts of illegal activities to the primate populations. Monitoring should be done for long term effects of human activities on primate populations and distributions.