Forest Fragmentation And Anthropogenic Disturbance: Implications On Plant Foods And Behavior Of The Tana River Mangabey (Cercocebus Galeritus Peters, 1879), Tana River County, Kenya

Abstract

Tana River mangabey, Cercocebus galeritus, is an endangered monkey, endemic to lower Tana River forest fragments in Kenya. The species is restricted in its geographical distribution and is threatened by habitat fragmentation and continuous anthropogenic disturbances. This study was conducted in Mchelelo and Mkomani forests within the Tana River National Primate Reserve (TRNPR). The objectives of the study were to determine the: diversity and density of Tana River mangabey plant food species in anthropogenically disturbed Mkomani forest and less disturbed Mchelelo forest fragments; anthropogenic disturbances and their magnitude in the two forest fragments; and behavioral comparison between the two sites. In each forest, lines were systematically established at equidistance of 200m running from the river bank to the edge of the forest. Along the lines, 20 by 20m quadrats were systematically placed at intervals of 50m from each other throughout for collecting vegetation data. To collect behavior data, full day animal focal sampling was conducted and the focal subjects were rotationally selected in each group. Behavior sampling was conducted in a manner that balanced data collection within the groups and was achieved through assigning focal subjects on a rotational basis for data recording. In the event of feeding by focal animal the consumed plant part was recorded. This study focused on two groups of the Tana River mangabeys, one occupying Mchelelo forest and the other Mkomani forest. The diversity of the food plant species was higher in Mchelelo (H' = 2.32) compared to Mkomani forest (H' = 2.04). Study findings showed that there was a significant difference in mean density and basal area values in Mchelelo and Mkomani. Furthermore, this study showed Phoenix reclinata, Ficus sycomorus and Synsepalum msolo were the most consumed plant species in Mkomani forest by the study group. In Mchelelo forest, the group preferred P. reclinata, F. sycomorus and Pavetta sphaerobotrys plant foods species. The study groups preferred fruits and seeds compared to leaves, young stem, gums and stem bark. The major anthropogenic disturbances were logging and palm leaf harvesting in both study sites. The most targeted plant food species for exploitation by community were P. reclinata, Polysphaeria multiflora and Lecaniodiscus fraxinifolius in Mchelelo forest whereas in Mkomani forest they preferred L. fraxinifolius, P. reclinata and Thespesia danis. Both study groups spent most of their time feeding compared to resting, moving and social interaction behaviour activities. In conclusion, Mkomani forest had less diversity, basal area, and density of plant species consumed by the Tana River mangabey compared to Mchelelo forest. P. reclinata and F. sycomorous were xii the most utilized plant food species by the community in both sites. This suggests that there is need to protect plant species consumed by the endangered Tana River mangabeys to provide the necessary food resources and improve diversity and density of vegetation in the forest especially in Mkomani forest. And also there is a need to replicate this study in other forest fragments along the Tana River which have varying anthropogenic activities and compare the results.