Differential Predation by Age and Sex Classes in Blue Wildebeest in Serengeti: Study of a Modern Carnivore Den in Olduvai Gorge (Tanzania)

Abstract

Age and sex selection of prey is an aspect of predator ecology which has been extensively studied in both temperate and African ecosystems. This dimension, along with fecundity, survival rates of prey and mortality factors other than predation are important in laying down the population dynamics of prey and have important implications in the management of species. A carnivore den located in the short-grassland ecological unit of the Serengeti was studied. Sex- and age- class (using five age categories) of the wildebeest remains recovered were analyzed through horn morphology, biometrics of the bones and tooth wear patterns. We compared our results with previous studies from lion and hyaena kills through multivariate analyses. Seasonality of the accumulation was analyzed through tooth histology. PCA and CVA results show that age class selection by predators depends on season, habitat-type, and growth rate of the wildebeest population. Female-biased predation was found to contradict classical hypotheses based on territorial male behaviour. The lion and spotted hyaena showed strong selection on age classes, contrary to previous studies. Migratory wildebeest sex ratio is regulated through differential predation by seasons and female deaths in the wet season are a trade-off for population stability. These data are crucial for an effective management of the species and the new method created may be useful for different carnivore species and their prey.

Lions as Bone Accumulators? Paleontological and Ecological Implications of a Modern Bone Assemblage from Olduvai Gorge

“…We understand that decades of research have not documented any accumulations made by lions. However, we also report here (and in [ 65 ]) that the purported lion behavior that may account for this bone accumulation is rather exceptional and caused by specific ecological factors that determine that the area is occupied by nomad lions. We do not believe that lions accumulate bones systematically as other carnivores (e.g., hyenas and, more sporadically, leopards) do.…”

“…An 8-month span was used to calculate the accumulation rate: 53 items per month. This shows a higher number of specimens collected than those reported for the spotted hyena and may be even higher since the bone accumulation seemed to be produced only during the early wet season (from November to January) [ 65 ]. Again, this feature is not consistent with the expected behaviour of the spotted hyena.…”

“…In fact, the two main predators of wildebeest in the Serengeti are the spotted hyena and lion [ 101 ]. Analysis of sex and age classes of the wildebeest recovered were carried out and compared with data of spotted hyena and lion kills in order to ascertain the carnivore responsible for the accumulation [ 65 ]. The results showed that the age selection by these predators in the Serengeti depend on the growth rate of the ungulate population, seasonality, and/or habitat.…”

“…The results showed that the age selection by these predators in the Serengeti depend on the growth rate of the ungulate population, seasonality, and/or habitat. There are no data available with all these criteria for the Serengeti ecosystem, and the five-age class method is the only one able to distinguish between the diet of the spotted hyena and lion [ 65 ]. The wildebeest bone accumulation was produced in the early wet season, when both the lion and spotted hyena select an equal sex ratio in their kills [ 65 ].…”

“…This implies that an accumulating agent has been actively bringing carcasses into the site between 2012 and 2013. Furthermore, the age-class profile documented at the site does not correspond with a catastrophic event [ 65 ]. The only prey present at the site is the blue wildebeest ( Connochaetes taurinus Burchell, 1823), making the Olduvai carnivore site (OCS) the first documented faunal assemblage in Africa containing the remains of just one ungulate species.…”