Sunday, August 2, 2009 - 1:10 PM

WK 15-1: Are non-native species different than natives? Comparisons of species distribution and abundance within regions

Dov F. Sax, Brown University

Background/Question/Methods - Non-native species are often perceived to have a variety of advantages over native species that could allow them to occupy more sites and to be more abundant at those sites, on average, than native species. I tested that assumption by comparing a number of distribution and abundance relationships for native and non-native plant species across three habitat types: 41 sites in coastal sage-scrub (southern California), 27 sites in xeric-sloped matorral (central Chile), and 25 sites in coastal strand-line (Rhode Island and Massachusetts).

Results/Conclusions - Few differences were found between native and non-native species in a series of comparisons that included: abundance-distribution relationships (i.e. the relationship between the number of sites species occur at versus average abundance within those sites) and site-frequency relationships (i.e. the frequency with which species occupy different numbers of sites within a region). These findings suggest, at least within the regions examined, that non-native species are not occupying the landscape in a way that is fundamentally different from that of native species.  Further work, examining these relationships across a greater number of habitats, is needed to determine the generality of these findings.