Structural continuity and multiple alternative stable States in Middle Pleistocene European mammalian communities

Community structure is defined as the distribution and frequency of occurrence of some ecological traits in a set of coexisting species. Many palaeoecological studies of mammal communities assume as valid a model of Community Structure Convergence (CSC), i. e. communities from similar environments should converge to a similar structure. However convincing evidences are known of the existence of multiple Alternative Stable States in ecological communities and similar structures in dissimilar environments have been found. The model of community convergence and the existence of multiple Alternative Stable States are tested here using data from a set of 24 Middle Pleistocene and 50 recent European mammalian communities. Community structure is compared using a multivariate approach. Species are assigned to one of 19 possible ecological groups and a multidimensional “eco-space” is computed based on the abundance of these groups of species in each community, using Principal Components Analysis. The dispersion of the communities in the “eco-space” is used as a measure of their community structure differences. While results indicate the existence of different structures in Glacial and Interglacial northern paleocommunities the considerable intra-group heterogeneity observed contradicts the predictions of the CSC model. The results support the existence of structural continuity (conservation of community structure despite concurrent changes in species composition) in the Iberian and Italian peninsulas during the Middle Pleistocene, as well as a model of cyclic disruption and assembly of paleocommunities with multiple Alternative Stable States in Northern Europe. Northern European assembly processes differed one from the other, giving rise to a community structure more varied than that found in Southern Europe.