Wc. Gasaway et al., PERSISTENT LOW-DENSITIES OF PLAINS UNGULATES IN ETOSHA NATIONAL-PARK,NAMIBIA - TESTING THE FOOD-REGULATING HYPOTHESIS, Canadian journal of zoology, 74(8), 1996, pp. 1556-1572
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.