Résumé
Aim: The “central-peripheral” hypothesis has provided a baseline for many
studies of population dynamics and genetic variability at species
distribution limits. Although peripheral populations are often assumed to
occur in ecologically marginal conditions, little is known about whether
they effectively occur in a distinct ecological niche. Location: Western
Mediterranean basin. Time Period: 2013-2014. Major taxa studied: A
cross-taxa analysis of 11 Mediterranean vascular plants. Methods: We
quantified variation in the ecological niche between populations at the
northern range limits of species in Mediterranean France and those in the
central part of the distribution in continental Spain or Italy. We
analyzed both the macro-ecological niche where populations occur in terms
of broad habitat and altitudinal range and the micro-ecological niche
where individual plants grow in terms of soil and structural biotic and
abiotic characteristics. Results: Most species occur in a single broad
habitat type common to central and peripheral populations and have a
narrower altitudinal range in the latter. In contrast, for the
micro-ecological niche we detected marked variation in several niche
parameters among central and peripheral populations. Although many
differences are species-specific some are common to several species. We
found a trend towards narrower micro-niche breadth in peripheral
populations. Main conclusions: Our results illustrate the importance of
studying the precise ecological characteristics where plants grow and the
pertinence of a multi-species approach to correctly assess niche
variation. The ecological originality of peripheral populations underlines
their evolutionary potential and conservation significance.