3 rd International Symposium on Weeds and Invasive Plants October 2-7, 2011 in Ascona, Switzerland [Type text] The Riddle of Gunnera tinctoria Invasions: a Particularly Irish Enigma B. Osborne, M. Fennell & C. Armstrong UCD School of Biology and Environmental Science, University College Dublin, Belfield, Dublin 4, Ireland ABSTRACT: Gunnera tinctoria invasions represent an often identified enigma: why should a spe- cies with a narrow ecological amplitude have the capacity to become such a significant invader? In Ireland, for instance, it is now recognised as one of the top thirteen invasive species. Consideration of its ecophysiology indicates that it should never be able to colonize areas subjected to even mild water deficits, although the impact of other environmental factors is unclear. Habitat-mapping of G. tinctoria in the west of Ireland indicates a preference for anthropogenic habitats. Rather surprisingly, coloniza- tion of organic soils, the dominant soil type in the region is poor. Analysis of G. tinctoria populations indicate that the invasive populations are genetically distinct and that gene flow may be an important factor contributing to invasive success. Stochastic evolutionary processes alone can explain the ob- served genetic variation, with no need for adaptive evolution. Genetic analysis, in conjunction with computer-based modelling, indicates that seed dispersal is the primary method for long distance propagule dispersal, despite the fact the initial belief that this species propagates solely asexually. However, few seeds germinate in the field, although they remain viable, with germination constrained by low soil temperatures. Projections of the impact of climate change on the future success of this species indicate that its distribution is likely to increase by the end of the century, with habitat-type playing the more significant role. Overall, these results indicated how little we know about what con- tributes to successful invasions and the significance of complex relationships among plant traits, habi- tat and climate. KEY WORDS: Gunnera tinctoria, ecological amplitude, habitat, genetic differentiation, water avail- ability 1 INTRODUCTION Although previous work has often demon- strated a positive relationship between the dis- tribution of a plant species in its native range and that in its invaded range, there are notable exceptions to this result that include particularly successful invaders with a restricted native range (Williamson and Fitter, 1996; Rejmanek, 1996). Whilst there is a tendency to infer a bio- logical, trait-based explanation for this, with suc- cess in the invaded range attributed to charac- teristics associated with success in the native range, a more recent analysis suggest that this is more likely due to the increased chance of species with a wide native range being moved by humans to other regions (Pysek et al., 2009). If this is the case there is no a priori reason to invoke a functional, trait-based reason for the success of a number of invaders, Corresponding author address: Bruce Osborne, UCD School of Biology & Environmental Sci- ence, UCD, Belfield, Dublin 4, Ireland. Tel:+35317162249 ; fax: +35317161153 Email:bruce.osborne@ucd.ie despite having a wide geographical range. It should also, perhaps be recognised that correla- tions based on a wide geographical spread does not necessarily imply a broad ecological ampli- tude, as species may occupy similar habitats in different geographically-separate locations. One notable plant invader with restricted ecological amplitude is Gunnera tinctoria. Despite a rela- tively broad latitudinal distribution it is confined to terrestrial habitats with a high water availabil- ity and moderate temperatures in both its native and introduced ranges (Osborne & Sprent, 2002). Whilst extensive invasive populations can be found in some introduced locations, this is not a feature of native habitats, where small isolated plants or small fragmentary populations comprising only a few individuals are more common (Osborne & Sprent, 2002). To assess the factors that may be important in contributing to invasive success in this and in other invasive plant species we report on as- pects of the ecophysiology, genetics, current, distribution and potential range expansion of G. tinctoria. These results indicate the difficulty of generalizations about the causes of plant inva-