Increasing numbers of small stock are prey to the black-backed jackal, posing a serious threat to small-stock farmers. Two scientists found the reintroduction of larger predators changes the jackal’s role as superior predator and forces this omnivore to change its diet. Roelof Bezuidenhout reports.
The recent reintroduction of lion and spotted hyena into the Addo Elephant National Park (AENP) has allowed scientists to study how the presence of these superpredators affects the diet of black-backed jackal. The jackal is omnivorous and SANPark’s managers fear it may be catching too many small to medium-sized game animals in the park. The study was conducted in the main Addo and Nyati sections of the AENP in the Sundays River region of the Eastern Cape. The Addo section comprises 148 000ha with the Nyati concession covering 17 000ha, including a large part of the Suurberg mountain range. Five biomes are represented in the AENP valley bushveld that covers nearly 70% of the area. Both the Nyati and Addo sections have the same plants and animals, with the exception of lion and spotted hyena, which were reintroduced only into the Addo section.
According to Christelle de Klerk of the Centre for African Conservation Ecology at the Department of Zoology at the Nelson Mandela Metropolitan University in Port Elizabeth, the study aims to create a better understanding of the jackals’ ecology in the park, and to see if there are seasonal variations in how they utilise prey. Christelle found that the diet of black-backed jackals varies significantly from Addo to Nyati and has been affected by the reintroduction of superpredators such as lion and spotted hyena.
Making the best of it
Christelle explains that the wide variety of prey species found in the jackal’s diet, as well as the variation in occurrences of each prey category, confirms that jackal are highly opportunistic feeders, taking whatever is most freely available and most easily obtained. They are avid hunters, taking anything from insects to medium-sized ungulates and although not common, cooperative hunting has been recorded. They readily scavenge off lion or hyena kills, or any other carcass they come across. They’ve also often been recorded eating rodents, fruit, birds and reptiles. Christelle discovered a significant increase in the amount of carrion in the jackal’s diet in Addo, as well as a decreased utilisation of small and medium-sized ungulates in Addo, compared to Nyati. “This suggests that reintroducing the large carnivores has had an effect on the jackals’ diet, both through intraguild competition and carcass availability. A guild is a group of species that uses similar, potentially limited resources.” She explains that the degree of overlap in prey species determines the degree of competition. “When comparing a carnivore with an omnivore, it’s expected that the omnivore will shift its dietary preference to invertebrates and small mammals if intraguild competition is severe.
This is also the case with larger versus smaller carnivores. If the larger members of a guild are removed it can be expected that the smaller-sized group left behind would respond by increasing the range of its prey size, due to a decrease in competition.” Observable results hristelle emphasises that while top predators are essential for the conservation of biodiversity, their role is complex and not simply a matter of predator-prey relationships. In essence, the study confirmed what was expected to happen after the lions and hyenas arrived. The jackals are getting more scavenging opportunities in the form of large mammals, including buffalo, killed by the large predators. While they don’t constitute a great portion of their diet, lions commonly prey on the same small and medium-sized ungulates that black-backed jackals catch. This means there is now competition for this food category. The result is that more carrion and fewer small to medium-sized game is being taken by jackals in Addo than in Nyati. Prey species are identified microscopically using hairscale imprints found in scats. Species found in the jackals’ diet that were larger than 50kg were classified as carrion.
New competition
How will the jackal population respond to the reintroductions? The answer is complex, says Prof Graham Kerley, director of the Centre for African Conservation Ecology. “Jackals now eat carrion from lion and spotted hyena kills and take fewer small antelope. Further, they are actively preyed upon by lions and hyenas, in a process called intraguild predation. So they have gone from being the top predators to having to fit in under the lions and hyenas. It will really be interesting to see how their numbers respond.” Contact Christelle de Klerk on 082 753 5406 or e-mail [email protected]
