Ecological transitions — But for whom? A perspective from the Pleistocene

This paper deals with the so-called Middle Pleistocene revolution, that is, the transition between the Early and Middle Pleistocene between 1.2 and 0.5 million years ago. Our knowledge about biotic changes during this transition has been so far largely based on studies of large mammals. Here we address the issue whether all faunal groups were equally affected. Three datasets have been used: (a) European large mammals present in the Middle and Late Pleistocene, (b) European fossil bird species recorded from the Early, Middle and Late Pleistocene of Europe, and (c) present-day birds currently classified in subfamilies that contain at least one Palaearctic representative species. Each species was allocated to all those geographical areas, climates, habitats in which it is present today; migratory status was also recorded. These datasets serve to undertake a biochronological analysis of mammal and bird groups, thus establishing patterns and processes of extinction and survival at the genus and species levels. The end of the Middle Pleistocene appears to have been a significant boundary in respect of herbivorous mammals, which suffered considerable depletion. In contrast, most genera and species of European birds in the Middle Pleistocene survived into the Late Pleistocene, even to the present day. Furthermore, at least 58% of the Middle–Pleistocene bird species were already present in the Early Pleistocene record. The most successful survivors in the Palaearctic Pleistocene were species from genera that had been the most climatically-tolerant during the late Cenozoic, usually from speciose and widely-distributed genera. We conclude that major transitions in Earth history have leant largely on biochronology and the perceived turnovers of faunas. Boundaries have usually depended heavily on changes to specific taxa of organisms. In this paper we show that what may appear as epic boundaries are largely scale- and taxon-dependent. Their usefulness must therefore be open to question. Here we advocate an individualistic and taxon specific approach in understanding the major ecological changes that have marked the history organisms.