Carnivores and humans during the Early and Middle Pleistocene in the Sierra de Atapuerca

Abstract

Food resource availability strongly influences the survival opportunities of all organisms and it is considered that meat was a relevant food resource for Homo populations during Early and Middle Pleistocene. The availability of resources, the intensity of competition with other secondary consumers and the ability to access meat and fat resources conditioned human presence in Europe in this time period. Mathematical modelling of palaeocommunity trophic dynamics is a powerful tool for investigating food resource availability and intraguild competition. We selected for this study the richer Early and Middle Pleistocenen faunal assemblages from Sierra de Atapuerca. Only assemblages with nine primary consumer and three secondary consumer species were included. Available resources for secondary consumers were obtained from a mathematical model based on Leslie Matrices. The model is developed under two premises: populations should be stable and net reproduction rate is equal to one. This model determines the age structures that make the populations of primary consumers stable, the average biomass that can be sustainably extracted in the long term, and its distribution in body size categories. In a second step, the distribution of resources among secondary consumers is also modeled and sustainable densities for each carnivore are estimated. Expected densities for secondary consumers are estimated from allometric equations. The ratio sustainable density/expected density is taken as a measure of the degree of fulfilment of the secondary consumers requirements. The faunal assemblage with the highest human fossil abundances is in TD6 1-2 level from Gran Dolina site, which coincides with the lowest competition intensity among secondary consumers. The single assemblage from Atapuerca dated to the early Middle Pleistocene TD8 level of Gran Dolina site presents higher competition intensity than the Early Pleistocene assemblages and lack evidence of human presence. Nevertheless, there are several assemblages with evidence of human presence at Atapuerca after 0.5 Ma, and some of them exhibit competition intensity values similar for TD8. Firstly, this model allows estimating food resource availability for the guild of secondary consumers and comparison of competition intensity between different faunal assemblages. Secondly, our results support an environment rich in trophic resources for secondary consumers at Sierra de Atapuerca during the late Early and early Middle Pleistocene. Competition intensity was higher during the early Middle Pleistocene than during the late Early Pleistocene. This results evidence that humans were able to successfully exploit the Atapuerca ecosystems even a moderately high levels of intraguild competition.