Stability in Pleistocene Mediterranean mammalian communities

The present paper evaluates the differences in community structure between nine mammalian paleocommunities from the late early Pleistocene to the late middle Pleistocene from Sierra de Atapuerca (Burgos, Spain). The magnitude of the differences inside this group of paleocommunities is compared with the heterogeneity observed in 43 recent Eurasian communities grouped by biome. A new method is used to compare community structure. Species are assigned to 1 of 23 possible ecological groups and a multidimensional “eco-space” is computed based on the abundance of these groups in each community using Principal Components Analysis (PCA). The dispersion of the communities in the “eco-space” is used as a measure of their differences in community structure. The group of paleocommunities from Atapuerca exhibits less heterogeneity than that observed inside groups of recent communities from a particular biome. Thus, it is concluded that a considerable constancy in community structure existed in the paleocommunities from Atapuerca along the Pleistocene. This stability contrasts with the existence of various climatic cycles and with the development of different plant communities at Atapuerca throughout this period. To explain the observed pattern, a theoretical model of community evolution is proposed. According to this model, only a limited number of community structures are possible in a given environment, although the exact configuration attained by a particular community depends upon historical and biogeographic factors. Once a community structure has been established, emergent mechanisms maintain it with minor changes (resilience) until a large perturbation disrupts the community and a new assembling process begins.