Faculty of Mathematics and Natural Sciences, University of Bonn, 53113 Bonn, GERMANY.
Explaining patterns of animal distribution and abundance is one major challenge of ecology. The availability of habitats and food as well as predation determines the coexistence of animal species. Thus, knowledge about abundance, distribution and resource partitioning is of direct relevance to conservation and management of animal populations.
The puku antelope (Kobus vardonii Livingstone, 1857) was investigated in Zambia with a focus on Kasanka National Park and on the Kafue Region, i.e. Kafue National Park and surrounding Game Management Areas. Data about autecological and synecological aspects of the puku’s ecology and population status were collected between 2009 and 2011 during different seasons.
Road surveys along line transects were conducted at different times during the dry season. Puku occurred in small to large groups. They preferred grassland where estimated population densities were 36.15 puku/km2 in Kasanka National Park and 14.66 puku/km2 in the Kafue Region, respectively. Puku were observed in lower numbers in intermediate habitats and in miombo woodlands. Local population densities of the puku reached up to almost 150 animals/km2. Puku assembled especially on floodplains, grasslands or next to rivers or lakes. For the survey period 2009/2010 in Kasanka National Park, a population size of 5,038 (3,268-7,238) puku was calculated. This is an eightfold increase since the survey in July 1994 and a result of the ongoing conservation work of Kasanka Trust Ltd. Assumed higher juvenile survival might positively affect the numbers of puku in Kasanka National Park, but may lead to differences in social organisation.
A reference collection of the epidermis of grasses was compiled for microhistological analyses of plant fragments in bovid dung samples in order to assess their diet and dietary overlap. Throughout all seasons and study regions, puku consumed almost exclusively grasses. Particularly, they fed on Panicum spp., Brachiaria sp., Sporobolus spp., Hyparrhenia/Andropogon grasses and Eragrostris spp. in different amounts depending on season, study region and sex. The puku’s dietary niche was broadest in the cool dry season and narrowest in the late rainy season. In Kasanka National Park, the analysis of puku dung from different sites revealed a high spatial variation in the puku’s diet which suggests an opportunistic choice of grass species.
In Kasanka National Park, there was a slight spatial overlap with sitatunga (Tragelaphus spekii). Between the puku and other bovids in Kasanka National Park, there was a slight dietary overlap during the cool dry season, but virtually no dietary overlap during the hot dry season. In the Kafue Region, puku and impala (Aepyceros melampus) occurred syntopicly. They had similar distribution patterns over the transect lines, but however, impala were encountered to a higher extent in woodlands and intermediate habitats. In the late rainy season, due to an increasing amount of grasses in the impala’s diet, the dietary overlap between the impala and the puku increased, while it was rather low in the cool dry season.
Thus, one reason for high population densities of the puku in the study regions might be a generally low dietary competition, especially in the dry season.
To assess the impact of predation on puku populations, scats of predators were collected. In Kasanka National Park, hair of the puku and the sitatunga was found to almost equal amounts in the scats of Nile crocodile (Crocodylus niloticus), which probably is the most important predator of the puku, while large terrestrial predators were generally rare. Whitetailed mongooses (Ichneumia albicauda) and African civets (Civettictis civetta) consumed puku presumably by scavenging only. In the Kafue Region, the puku occurred in the scats of lion (Panthera leo) and of spotted hyena (Crocuta crocuta) to considerable amounts, but for none of them, the puku was the preferred prey. Instead, puku were consumed in accordance to its availability. Predation pressure of large terrestrial predators appeared rather low in Kasanka National Park and in consequence does not limit the population of puku. In the Kafue region, predation was suggested to be higher and possibly regulates the puku’s population to a greater extent.
However, considering the higher numbers of juveniles, male-groups and individuals in poor body condition, bottom-up regulation via rainfall and food is very likely to act particularly on the puku’s population in Kasanka National Park.
The activity patterns of the puku showed that it is not predominantly diurnal. While puku grazed mainly at dawn, they rested during the day.
During this study, a lot of insight into the Zambian ecosystem could be gained, reaching from grasses over antelopes to carnivores. New information is presented about population densities and social organisation of the puku. For the first time in Zambia, the food plants of the puku were investigated by microhistological analyses of dung and the circadian activity patterns of the puku were assessed. Thus, besides confirming the few existing knowledge, this study revealed new facts about the puku’s ecology and population status in Zambia.