Title

The distribution of Carex curvula-dominated communities in Europe: an attempt at a functional and historical interpretation (pdf)

Jury Commitee:

Philippe KÜPFER, Pr., Université de Neuchâtel, rapporteur
Sandra LAVOREL, C.R. (CNRS), Centre d’Ecologie Fonctionnelle et Evolutive, Montpellier, rapporteur
Richard BLIGNY, D.R. (CNRS), Université J. Fourier - Grenoble I & CEA Grenoble, co-directeur
Richard MICHALET, Pr., Université de Bordeaux, examinateur
Rémy SADOUL, Pr., Université J. Fourier - Grenoble I, examinateur
Pierre TABERLET, D.R. (CNRS), Université J. Fourier - Grenoble I, directeur

Summary

The plant communities dominated by Carex curvula (s.l.) are widespread alpine meadows of the temperate European mountain ranges. The species Carex curvula exhibits two ecotypes: Carex curvula subsp. curvula (Cc) and Carex curvula subsp. rosae (Cr). The goal of this work is to shed light on the determinisms of the distributional patterns of these two ecotypes, and of the floristic assemblages in which they occur.

From a functional perspective, this work aims at defining the niche attributes of the two ecotypes and at exploring the underlying mechanisms of the contrasted performance of Cc and Cr along the environmental gradients. Species - environment relationships in the high-elevation meadows of the french Alps are studied using a direct gradient analysis. The niche separation between Cc and Cr along mesotopographical and disturbance gradients is pointed out. Cr is occurring on windy, highly disturbed convex sites, whereas Cc is preferentially established on more snowy, and less disturbed leewards or footslopes. We then adress the impact of biotic interactions on the realized niche of alpine species along these environmental gradients. An experimental study of plant-plant interactions along elevational and mesotopographical gradients reveals the predominance of facilitation in the most exposed communities, including those dominated by Cr. Finally, a comparative and quantitative analysis of life history traits along the same gradients is providing first insights on the functional strategy of alpine plants. In this regard, the adaptive significance of traits variations between Cc and Cr is discussed.

From an evolutionnary perspective, this work aims at determining the origin and the quaternary history of Carex curvula in Europe. The genetical bases of the ecotypic differentiation is adressed using the AFLP DNA-fingerprinting methods. The results indicate that each ecotype is monophyletic and may have originated by ecological speciation. The recent history of Carex curvula is also characterized by the occurrence of gene flow between both ecotypes in secondary contact zones. A phylogeographic study of Cc using the same molecular markers suggests that Pleistocene refugia were presumably located in the eastern part of the Alps. A main colonisation route from east to west is held as the most parsimonious hypothesis to explain the current distribution of genetic diversity of Cc in the Alps. Whilst long-term separation of populations in the Balkans and Carpathians is supported, the populations of the Pyrenees are closely related to those of the western Alps and are possibly of recent origin.

To conclude, we propose a model emphasizing the intricacy of historical and ecological factors in order to explain the current distribution of Carex curvula-dominated communities.