Decline of large mammals in the Katavi-Rukwa ecosystem of western Tanzania
In the Katavi-Rukwa ecosystem of western Tanzania, aerial censuses carried out between 1988 and 2002 show that populations of several large ungulate species had declined. Five competing factors that could be responsible for these changes were investigated. (i) Rainfall increased slightly over 25 years and (ii) no obvious outbreaks of disease were witnessed, suggesting that populations are not suffering food shortages or disease. (iii) Large predators live at low densities and are not increasing, and estimates suggest that that predation is unlikely to impact larger prey species. (iv) Some assessments of illegal hunting indicate little influence on herbivore populations but one measure points to giraffe, hippopotamus, warthog and perhaps other species being adversely affected. (v) Tourist hunting quotas of lions and greater kudu in hunting blocks appear high and there are indications that both may be declining. Preliminary data, approximate calculations and elimination of hypotheses point to anthropogenic factors being partly responsible for changes in this ecosystem and constructive recommendations are made to alter these. More generally, this study highlights the importance of monitoring in conjunction with collecting diverse data when trying to stop population declines before they become too serious.
Key words: hunting, lions, population changes, predation, ungulates.