The Cape fox (Vulpes chama) and bat-eared fox (Otocyon megalotis) are sympatric with the black-backed jackal (Canis mesomelas) over much of Southern Africa. Put more simply, all three share the same ancestor and geographic distribution. But it seems that competition with, and predation by, jackals may suppress local populations of both fox species. This finding came from a three-year study by Dr Jan Kamler of the Wildlife Conservation Research Unit at the Department of Zoology of Oxford University.
“While the two foxes live in harmony with one another, the black-backed jackal appears to be a threat to both,” says Dr Kamler. “Across 22 study sites in South Africa where control measures have reduced black-backed jackal numbers, fox numbers have increased. Conversely, where jackal numbers increased over large areas in the 1980s, fox numbers declined.”
The researchers radio-collared and monitored 11 Cape foxes, 22 bat-eared foxes, and 15 black-backed jackals on a game ranch near Kimberley. This was the first detailed investigation into the effects of the two larger canids on the small Cape fox – a 4kg predator suspected by many farmers of catching newborn lambs. The size of the species’ home ranges was found to be 27,7km² for the Cape fox, 5km² for the bat-eared fox, and 17,8km² for jackal family groups. Home ranges overlapped between species, although core areas overlapped less, with Cape foxes and jackals overlapping the least.
Both fox species used jackal core areas less than expected for their den sites, suggesting that areas outside jackal core areas were used as refuges by foxes. Diets overlapped little, with the bat-eared fox, which eats mostly termites and fruit, overlapping the least. Jackals caught mainly smaller game, such as springbok. The Cape fox’s diet comprised mostly (70%) small mammals such as rodents, but they also ate insects and fruit on occasion.
“Should increasing Cape fox populations ever become a conservation objective, managers will have to consider jackal numbers in addition to food and habitat – jackals kill foxes because they compete for territory,” says Dr Kamler. In another study on the same game ranch and two adjacent sheep farms, he found that where jackal density was high, the Cape fox was sometimes absent. (The game farm had a much higher population of jackal than the stock farms.)
“Medium-sized carnivores have benefited from the widespread extermination of large carnivores,” says Dr Kamler. “Bat-eared fox and black-backed jackal numbers have increased in the past 20 years, coinciding with a decrease in Cape fox numbers.” Dr Kamler’s study confirmed that jackal numbers affected both fox species. “Predation by jackal was responsible for 71% of Cape fox deaths and 67% of bat-eared fox deaths.
Black-backed jackals also appeared to negatively affect the home range and distribution of the Cape fox, as well as group sizes of the bat-eared fox. Cape foxes avoided jackal core areas, and were forced to range far for food,” he says. The Cape foxs established dens only when more than 2km from jackal dens. “There were few places on the game farm where Cape foxes could raise litters safely. This caused the Cape fox density to be 64% lower on the game farm than on the sheep farms,” says Dr Kamler.
It seems that in the presence of jackals, bat-eared foxes stayed in larger groups for better protection against predation.
“This has implications for disease control, as larger group sizes and more overlapping home ranges of bat-eared foxes on the game farm probably increased their susceptibility to epizootics, diseases that often occurred there but not on the sheep farms,” says Dr Kamler.
Resource Partitioning among Cape Foxes, Bat-eared Foxes and Black-backed Jackals in SA, The Journal of Wildlife Management 76(6):1241–1253; 2012; DOI: 10.1002/jwmg.354
Email Dr Jan Kamler at [email protected]