Expansion of a globally pervasive grass occurs without substantial trait differences between home and away populations
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The global expansion of species beyond their ancestral ranges can derive from mechanisms that are trait-based (e.g., post-establishment evolved differences compared to home populations) or circumstantial (e.g., propagule pressure, with no trait-based differences). These mechanisms can be difficult to distinguish following establishment, but each makes unique predictions regarding trait similarity between ancestral (‘home’) and introduced (‘away’) populations. Here, we tested for trait-based population differences across four continents for the globally distributed grass Dactylis glomerata, to assess the possible role of trait evolution in its worldwide expansion. We used a common-environment glasshouse experiment to quantify trait differences among home and away populations, and the potential relevance of these differences for competitive interactions. Few significant trait differences were found among continents, suggesting minimal change during global expansion. All populations were polyploids, with similar foliar carbon:nitrogen ratios (a proxy for defense), chlorophyll content, and biomass. Emergence time and growth rate favored home populations, resulting in their competitive superiority over away populations. Small but significant trait differences among away populations suggest different introductory histories or local adaptive responses following establishment. In summary, the worldwide distribution of this species appears to have arisen from its pre-adapted traits promoting growth, and its repeated introduction with cultivation and intense propagule pressure. Global expansion can thus occur without substantial shifts in growth, reproduction, or defense. Rather than focusing strictly on the invader, invasion success may also derive from the traits found (or lacking) in the recipient community and from environmental context including human disturbance.
KeywordsInvasion ecology Common-environment trial Competition Plant functional traits Orchard grass
Thanks to Julie Maniecki, Erin Leclair, Greg Baute, Paul Kron, Sarah Baldwin, Tannis Slimmon, Mike Mucci, Pedro Tognetti, Enrique Chaneton, Walter Martin, Karl Fiander, Jennifer Firn, Hafiz Maherali, Merritt Turetsky, John Klironomos, and Rieger-Hoffmann. Seed importation and the destruction of plant material at the end of the experiment followed the guidelines of the Canadian Food Inspection Agency. Funding provided by NSERC (Canada), the European Union through the European Regional Development Fund (Estonian Center of Excellence FIBIR) (Estonia), FCEyN and CONICET (Argentina), the International Bureau of the Federal Ministry for Education and Research (Germany), and by the New Zealand Foundation for Research, Science and Technology grant C09X0502.
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