Abstract
Calcareous grasslands belong to the most diverse, endangered habitats in Europe, but there is still insufficient information about the origin of the plant species related to these grasslands. In order to illuminate this question, we chose for our study the representative grassland species Hippocrepis comosa (Horseshoe vetch). Based on species distribution modeling and molecular markers, we identified the glacial refugia and the postglacial migration routes of the species to Central Europe. We clearly demonstrate that H. comosa followed a latitudinal and due to its oceanity also a longitudinal gradient during the last glacial maximum (LGM), restricting the species to southern refugia situated on the Peninsulas of Iberia, the Balkans, and Italy during the last glaciation. However, we also found evidence for cryptic northern refugia in the UK, the Alps, and Central Germany. Both species distribution modeling and molecular markers underline that refugia of temperate, oceanic species such as H. comosa must not be exclusively located in southern but also in western of parts of Europe. The analysis showed a distinct separation of the southern refugia into a western cluster embracing Iberia and an eastern group including the Balkans and Italy, which determined the postglacial recolonization of Central Europe. At the end of the LGM, H. comosa seems to have expanded from the Iberian refugium, to Central and Northern Europe, including the UK, Belgium, and Germany.
Highlights
Calcareous grasslands are among the most species-rich ecosystems in Central Europe (Korneck, Schnittler, & Klingenstein, 1998; Sadlo, Chytry, & Pysek, 2007; WallisDeVries, Poschlod, & Willems, 2002), and many studies have been conducted to understand the ecological mechanisms behind this observation (Cornish, 1954; Dutoit &Alard, 1995; Gibson & Brown, 1991; Kahmen, Poschlod, & Schreiber, 2002; Poschlod, Kiefer, Trankle, Fischer, & Bonn, 1998; Römermann, Bernhardt-Römermann, Kleyer, & Poschlod, 2009)
amplified fragment length polymorphisms (AFLPs) analysis is a powerful tool in revealing glacial refugia and postglacial immigration processes, as we show here on an example of the calcareous grassland species H. comosa
The traditional latitudinal temperature gradient as major parameter was extended by a longitudinal humidity gradient which both work in tandem defining the suitable habitats during the last glacial maximum (LGM)
Summary
Calcareous grasslands are among the most species-rich ecosystems in Central Europe (Korneck, Schnittler, & Klingenstein, 1998; Sadlo, Chytry, & Pysek, 2007; WallisDeVries, Poschlod, & Willems, 2002), and many studies have been conducted to understand the ecological mechanisms behind this observation Recent studies suggested several additional refugia for temperate species beyond these peninsulas These cryptic northern refugia are postulated for higher latitudes than the expected southern refugia (Bhagwat & Willis, 2008; Bylebyl, Poschlod, & Reisch, 2008; Magri et al, 2006; Willis & van Andel, 2004) and are defined as climatic islands with favorable conditions (Stewart & Lister, 2001), surrounded by unsuitable conditions. As soon as climate became warmer in the postglacial, recolonization of the surrounding steppe–tundra vegetation may have started from there In this context, it must be mentioned that the following reforestation might have been held back before the Neolithic (see Bush, 1988), either by human with fire or by megaherbivores enlarging the potential habitats of calcareous grassland species besides naturally treeless sites like cliffs (Pokorný, Chytrý, & Juřičková, 2015; Svenning, 2002). We asked the following questions: (i) Which refugial areas served as source for the postglacial immigration of H. comosa to Central Europe? (ii) Where were the main migration routes from the refugia to Central Europe? (iii) Is there evidence for the long-t erm survival of H. comosa in cryptic northern refugia?
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