Competition, Kleptoparasitism, and Hunting Group Size

            According to Carbone, Du Toit, and Gordon (1997), the Wild dog population has nearly vanished from the Serengeti plains. During the same period in the Serengeti, the hyena population has more than doubled, which is thought to be due to a substantial increase in the wildebeest and gazelle populations. The shift in population density of these two species has resulted in a significant increase in the ratio of hyenas to wild dogs in the Serengeti. Given that wild dogs are substantially smaller than hyenas, they can be driven off fresh kills by relatively few hyenas. This has been documented in a number of studies (see Eaton 1979; Fanshawe & Fitz Gibbon, 1993; Creel & Creel, 1996) which found a negative relationship between wild dog and hyena densities across six ecosystems.

            A simple model was developed to explore how variation in wild dog hunting group size in the Serengeti influences defense of kills against hyenas, and the trade-off effects this has on intake rate per dog for a given prey size. The article's primary focus is upon the question of whether increased access time at a kill (afforded by group defense against hyenas) compensates for the reduction in each dog's potential share of the carcass and, hence, whether adjustment of hunting group size is a strategy that wild dogs can employ against kleptoparasitism. Of secondary interest is the articles examination of the impact of kleptoparasitism on average profitability of different prey with varying hunting group sizes.

            The authors found that while kleptoparasitism substantially influences the amount of time a hunting group can access a kill, increases in access time with increased hunting group size rarely fully compensate for the reduction in each dog's share of the carcass due to ‘scramble competition’ among the dogs. This was displayed in a profitability index, which included limitations of the probability of capturing different sized prey, gut capacity, food depletion and access time, suggesting that the smaller the hunting group the more vulnerable it is to kleptoparasitism. Where hunting groups  of 1-2 would be particularly vulnerable because they are unable to fully satiate themselves before spotted hyenas take over their kills. Notably, intermediate-sized hunting groups may be most effective at meeting nutritional demands over a range of prey sizes.

Works Cited

Carbone, C., Du Toit, J. T. & Gordan, I. J. (1997). Feeding success in african wild dogs: Does      

kleptoparasitism by spotted hyenas influence hunting group size? Journal of Ecology (66), 318-326.