Are plasticity in functional traits and constancy in performance traits linked with invasiveness? An experimental test comparing invasive and naturalized plant species
The role of phenotypic plasticity in plant invasions is among the most often discussed relationships in invasion ecology. However, despite the large number of studies on this topic, there is little consistency. Reconsideration of the role of plasticity by distinguishing two substantially distinct trait-groups, performance traits (contributing directly to fitness) and functional traits (influencing fitness indirectly), could form a more operative framework for comparative studies. In the current study we expect that invasive species benefit from being plastic in functional traits, which allows them to maintain a more constant performance across different environmental conditions compared to non-invasive alien species. We compared invasive and naturalized non-invasive alien plant species by their germination (20 species), their vegetative (10 species) and their reproductive (four species) responses to three different levels of water, light and nutrient availability in a common garden experiment. Used traits were classified into performance (germination ratio, total biomass, seed number) and functional traits (time to germination, root:shoot ratio, specific leaf area, reproductive allocation). We found that invasive and non-invasive species responded similarly to environmental factors, except for example that invasive species germinated earlier with decreasing light conditions or, surprisingly, non-invasive species reacted more intensely to increased nitrogen availability by having a superior ability to achieve greater biomass. The two groups were equally plastic in all the germination and vegetative traits measured but the reproductive traits, since higher plasticity in relative reproductive allocation and higher constancy in reproductive performance showed a pronounced relation with invasiveness.
KeywordsAlien species Biomass Fitness Germination Invasion ecology Light Nitrogen Water
We are very grateful to J. Tökölyi for help with data analysis, to L. Bartha, M. Beldean, E. Fodor, É. Juhos, E. Kocsis, E. Kőműves, T. Kuhn, and H. Tyirla for their assistance during the experiments, and to M. Beldean, L. Filipaş, P.L. Pap and C.I. Vágási for their help in seed collection. We thank the “Alexandru Borza” Botanical Garden from Cluj-Napoca, especially Prof. V. Cristea and G. Feszt, for ensuring the necessary infrastructure during the experiment. This work was supported by a BOF-IWS grant from the University of Antwerp.
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