Yan Sun1, Urs Schaffner2, Ragan M. Callaway3, John L. Maron3 and Heinz Müller-Schärer1
1Department of Biology, Ecology and Evolution, University of Fribourg, Chemin du Musée 10, 1700 Fribourg, Switzerland
2CABI, Rue des Grillons 1, 2800 Delémont, Switzerland; 3Division of Biological Sciences, University of Montana, Missoula, Montana, USA
The steep rise of research on the causes and consequences of biological invasions over the past decades has led to the emergence of a new discipline within Ecology and Evolution. Due to the distinct Environment × Genotype interactions and thus novel eco-evolutionary associations in the introduced range, studies of invasions have yielded novel insights into key ecological and evolutionary issues. However, invasion science has recently received criticism from academia on its “raison d’être” as a distinct discipline, especially fueled by the debate whether origin matters for invader impact. Here, we explore determinants of abundance and impact of invasive alien plants (IAP), specifically the contribution of evolutionary novelty, and thus, if origin matters. Recent macroecological studies that remained observational found that the size (e.g. height, biomass) and abundance of IAP are generally similar in their native (home) and introduced (away) range, while single species studies often found clear origin effects.
To advance the discussion on when and how does origin matter in invasion ecology, we first argue that it is necessary to address two aspects fundamental to the discussion, i.e. the selection of species in tests for possible origin effects, and the suitability of the methodologies used in informing the ‘origin matters’ debate. Secondly, we reviewed 125 studies dealing with possible origin effects in plant invasions and indeed found that the research setting and the level of manipulation highly determined whether an origin effect was found or not. Origin effects of invasive alien plants were found more often in experimental (i.e. common garden and growth chamber) settings with less focal species studied, as compared to open field and observational studies with high numbers of focal species. We then contrast this approach to a growing list of studies that have examined one very potent invader, Centaurea stoebe (Asteraceae). Here, we found that origin clearly matters for impact, both ecological and evolutionary processes contribute to its invasion success, and, thus patterns and mechanisms of neighbour impacts are not transferable between ranges. This has important consequences for management decisions, since impact is highly context-specific and not an inherent species attribute. Finally, we discuss both the strengths and weaknesses of the “macroecological” versus “single species” approach and propose that more studies are needed at the intermediate level of the spatial setting and environmental control, such as in replicated manipulative open field settings with clearly defined focal species in order to better understand the mechanisms driving invasion success, especially their abundance and impact in novel environmental settings.