Djagoun, C. A. M. S. (2013)
PhD, University of Abomey-Calavi
This thesis endeavours to understand how grazing and browsing herbivores co-exist, with special emphasis on understanding the mechanisms of competition and facilitation over temporal and spatial scales. We focused on feeding ecology and habitat use study of the free ranging bovid species of Pendjari Biosphere Reserve in North western Benin. Here we used stable light isotope analysis of faeces to identify, as well as quantify bovid food selection, diet niche segregation and habitat selection indices (Manly’s alpha) were calculated for each bovid species to assess if habitat use differed in each species across hunting and non-hunting zones. While presence/absence data were used in resource-selection functions based on Generalized Linear Mixed effect Model to examine how bovid species distribution were related to habitat structure and composition, landscape structure and human disturbance. Additionally, detailed data on the time-budget were collected through focal animal observation technique to determine whether the time budget activities of Bohor reedbuck, living in sympatric system was affected by vegetation cover and to test if herd size, position in herd, the age and sex affect vigilance efficiency. Chapter 1 dealt with the background, starting research objectives, research questions and the thesis structure while chapter 2 dealt with the study area and study animal. In Chapter 3, we analyzed bovid species habitat use and distribution with respect to habitat structure (micro and macro-habitat), landscape characteristics, and human disturbance factors in West Africa, a semi arid landscape, where bovid occupy the Biosphere Reserve characterized by different managed areas. We observed a clearly stronger avoidance towards opened habitats in the hunting zone than in the non hunting zone for the hartebeest, oribi, roan, kob, waterbuck and reedbuck, while the ecological and behavioural plasticity was most pronounced in the grey duiker, red-flanked duiker, bushbuck and buffalo which didn’t show any shift in habitat use across the managed areas. Besides habitat preferences attributed to each bovid species at landscape level, bovid species’ resource selection was influenced on a small scale by other factors such as habitat structure, landscape characteristics, and human disturbance factors suggesting that bovid species are influenced by a range of factors operating at different scales. Chapter 4, analyzed the proportions of C3 browse:C4 grass in the diets of 11 bovid species in Pendjari Biosphere Reserve, Benin, West Africa. Of these, eight were expected to be grazers (buffalo, reedbuck, waterbuck, hartebeest, kob, oribi, roan and topi), and three browsers (red-flanked duiker, bushbuck and common duiker). Carbon isotope results from faeces of PBR bovids implied that only six species (buffalo, waterbuck, hartebeest, kob, roan and topi) had primarily C4 grass-dominated diets, whereas five species focused largely on C3 vegetation, i.e. browse (reedbuck, oribi, red-flanked duiker, bushbuck and common duiker). Given the discrepancies in % C4 in the diets of bovids from PBR compared with literature for other parts of Africa, it is clear that there is spatio-temporal dietary flux in many bovid species. Bovid diets are, to some extent, habitat-specific and averaging of % monocots in diet from continent-wide field studies does not adequately represent dietary diversity among African bovid species. Chapter 5 studied an assemblage of eleven bovid species in Pendjari Biosphere Reserve and tested two nutritional hypotheses for the ecological diversity of ungulates, the browser/grazer (diet type) and diet quality models. Results show that, contrary to many predictions, body mass and diet type are not related, but these data confirm predictions that the diet quality decreases with increase in body size, both in dry and wet season. Our findings also show numerous patterns in resource partitioning amongst the 11 bovid species studied, suggesting that different species used different dietary resource in contrasting ways. We concluded that in our study area, due to abundant resources and low herbivore densities, especially in the wet season, niche breadth and diet overlap remain large, because there is no need for herbivores to specialize and to avoid competition over scarce resources. Chapter 6, examined seasonal habitat features and diet partitioning in sympatric bovid species using waterbuck (Kobus ellipsiprymnus) and western kob (Kobus kob) as model species. In support of niche partition hypothesis, diets of western kob and waterbuck differed significantly along both faecal selection axis (?13C and ?15N) during the resource scarcity period of dry season as opposed to wet season when there is resource abundance. Western kob and waterbuck resource partitioning does not occur only on the basis of diet segregation but also some habitat variables play an important role in the co-existing system with “distance to water” emerging as most important discriminatory variable.
Chapter 7, provided a valuable contribution to our knowledge on how coexistence in sympatric African mammal herbivores affect behaviour and vigilance of ungulate using Bohor reedbuck as model species. Our study adds to the large amount of evidence demonstrating the herd-size effect on ungulate vigilance, and it also adds the importance of sympatric grouping system in Bohor reedbuck behaviour and vigilance efficiency. In addition, habitat type and grass height did not affect the vigilance behaviour of the Bohor reedbuck. Our study has also shown that within-herd spatial position is an important factor to be taken into account in the study of vigilance behaviour. However, further study is needed to investigate the possible sex-specific functions and targets of vigilance behaviour and the effect of within-herd spatial position with respect to the herd direction in the field. The last chapter (Chapter 8) presented a general discussion and conclusions on issues tackled in this thesis. Although each part of the study was approached independently, the various elements combined well providing an indication of the factors driving coexistence in bovid community of Pendjari Biosphere Reserve.
Key words: Bovid, diet, habitat use, coexistence, Pendjari, niche segregation, seasonality, Benin