Quaternary refugia in centers of endemism
Centers of endemism are quite logically the focus of much conservation efforts. In these areas, rare specialist species attract most interest, whereas generalist species that co-occur do not draw as much attention. Yet if we consider relevant community interactions, specialist species are known to interact mostly with generalist species, not with other specialists. Hence, we should not solely focus on rare endemics if we are to understand how communities work in centers of endemism. Focusing on common generalist species should yield a deeper understanding of the history and environmental factors that have determined the very existence of these centers of endemism. Common generalist species have been the object of paleoecological, genetic and demographic studies, with a focus on Quaternary refugia and local adaptation, typically conducted independently of community studies aiming at characterizing the diversity of threatened endemics.
Here, we show that integrated studies showing that centers of endemism have also acted as glacial refugia, due in part to the difficulty to demonstrate in situ persistence of species at a given locale during extended periods of time. We first provide a summary of available knowledge on the genetic structure and adaptation of generalist species in glacial refugia, using European beech, one of the most abundant tree species in Europe, as case study. We show that beech refugia tend to occur in environmentally unusual areas characterized by highly stable and mild climate, which have allowed them to persist in situ though both glacial and interglacial episodes. Such extended persistence has resulted in a complex genetic structure, favoring local adaptation and the persistence of ancient characters. Such stability should have also favored populations of rare associated species, making these areas important zones not only for the conservation of genetic resources but also for the conservation of associated biodiversity. More studies are needed to evaluate this association, taking advantage of new genetic and paleoecological approaches based on soil macrofossil charcoal analyses, while exploring associated biodiversity in a more systematic way.