PERSISTENT LOW-DENSITIES OF PLAINS UNGULATES IN ETOSHA NATIONAL-PARK,NAMIBIA - TESTING THE FOOD-REGULATING HYPOTHESIS

Declines and persistent low densities of plains ungulates during 1960- 1994 in Etosha National Park (Etosha) compromise Namibia's efforts to develop a wildlife- and tourist-based economy and maintain its nationa l biodiversity. Plains ungulates are blue wildebeest (Connochaetes tau rinus), plains zebra (Equus burchelli), springbok (Antidorcas marsupia lis), and gemsbok (Oryx gazella). We tested the hypothesis that plains ungulate populations were well below their food-resource ceiling (FRC ) and predicted that widely variable rainfall (food production) would have no significant effect on birth and survival rates; alternatively, ungulates regulated near their FRC would display strong responses to variable rainfall through negative feedback on fertility, yearling rec ruitment, and mortality. Data supported the hypothesis that Etosha's p opulations were well below their FRC. The pregnancy rate of springbok was high during drought. Recruitment of all four species was not posit ively related to rainfall. Mortality was not negatively related to rai nfall, and high mortality did not occur during droughts. Given the hig h recruitment of Etosha's stable or declining populations, we hypothes ize that high adult and yearling mortality resulting from anthrax and predation was the primary process preventing population growth. Manage ment aimed at maintaining or increasing the numbers of Etosha's plains ungalates currently need not emphasize habitat enhancement.