Figure 6. Impala and elephant populations in the Olifants West Nature Reserve, 2007-2012. Impala populations appear to be increasing, but average density of mixed feeders, as well as elephant populations, have decreased in the last five years.
Carnivores Carnivore population densities have followed similar trends to common prey, which is not too surprising, since their populations are partly regulated by prey availability (Fig. 7). However, certain species have showed alarming decreases in density. Leopard populations in Balule decreased by 63% between 2011 and 2012 (Fig. 8), although this figure is probably exaggerated by the fact that leopard are difficult to spot from helicopters. In Olifants West, carnivore populations appear to be increasing slightly (Fig. 9). This could be because these species are still recovering from persecution in the area, or could be a response to habitat changes.
Average predator-prey populations 3
Log10 of population
2.5 y = 0.0347x + 2.0623 R² = 0.6175
2
Common prey
1.5 Carnivores
1 0.5
y = 0.056x + 0.2256 R² = 0.512
0 1999
2001
2003
2005
2006
2007
2008
2009
2011
2012
Figure 7. Average populations of predators in Balule. Data from the 2010 helicopter count was excluded because no predators were recorded that year. However, the complete absence of predators was probably due to lack of visibility during aerial counts, rather than the animals’ absence. The population of “common prey” was calculated from the sum of counts for giraffe, kudu, warthog, buffalo, blue wildebeest, plains zebra, nyala, impala, and steenbok, the most common mammal prey taken by lions and leopards in the OWNR.