Variation in dispersability among mainland and island populations of three wind dispersed plant species B. Fresnillo, B. K. Ehlers Institute of Biological Sciences, Department of Ecology and Genetics, University of Aarhus, A ˚ rhus, Denmark Received 21 March 2007; Accepted 17 September 2007; Published online 4 December 2007 Ó Springer-Verlag 2007 Abstract. Reduced dispersability of species living on islands relative to mainland has been documented in both plants and animals. One evolutionary scenario explains this trend by strong selection against dis- persal, once the species has reached the island, to reduce dispersal out to sea. In this study, we compare the dispersal ability of three wind dispersed plant species (Cirsium arvense, Epilobium angustifolium, and E. hirsutum) from populations on mainland and three islands. Dispersal ability was estimated directly as drop time of diaspores, and indirectly using a morphological measure relating the weight of the diaspore to the size of the pappus (Cirsium) or seed hairs (Epilobium). Positive correlation between the morphological measure of dispersal ability and drop time of diaspores were found for all study species. Dispersal ability varied significantly among mainland and islands, and among species. C. arvense showed a significant reduction in dispersal ability on islands compared to mainland, whereas the reverse was found for the two Epilobium species. Overall Epilobium diaspores had a 2–4 times higher dispersability than C. arvense, indicating that degree of isolation of islands vary among study species. Significant differences in dispersability among plants within populations were detected in all species suggesting that this trait may have a genetic component. Keywords: Diaspore; mainland; island; pappus; seed hair; wind dispersal Introduction Dispersal of organisms away from their place of birth plays important roles for the distribution, range expansion and abundance of a species, and also in determining the spatial and genetic structure of populations at local and landscape scales. (Levin et al. 2003). In sedentary organisms like plants, individu- als move in space mostly as seeds. The dispersal mode adopted by a plant species is frequently associated with plant attributes and its habitat (Hughes et al. 1994). Dispersal ability is often related to particular morphological structures of the diaspores (seed or fruit). Species with wind dispersed seeds may evolve to small seeds with high surface/volume ratio (Howe and Smallwood 1982), or develop plumes or wings facilitating aerial transport (Burrows 1975, Green 1980). The morphological traits affecting seed dispersal are length and shape of plumes (e.g. pappus or seed hairs) and the mass and config- Correspondence: B. K. Ehlers, Institute of Biological Sciences, Department of Ecology and Genetics, University of Aarhus, Ny Munkegade build. 1540, 8000 A ˚ rhus C, Denmark e-mail: bodil.ehlers@biology.au.dk Pl Syst Evol 270: 243–255 (2008) DOI 10.1007/s00606-007-0615-1 Printed in The Netherlands Plant Systematics and Evolution