Evaluating differences in the shape of native and alien plant trait distributions will bring new insights into invasions of plant communities

Abstract

Failure to quantify differences in the shape of inter-specific trait distributions (e.g., skew, kurtosis) when comparing co-occurring alien and native plants hinders the integration of biological invasions and plant community ecology. Within a plant community, understanding the circumstances that lead to the shape of the inter-specific distribution of one or more functional plant traits being unimodal, bimodal, multimodal or skewed has the potential to shed new light on community vulnerability to invasion, subsequent ecosystem impacts and the selection pressures (e.g., stabilizing, directional or disruptive) acting upon native and alien species. Ignoring differences in the shape of inter-specific trait distributions of alien and native species could miss important insights into plant invasions, including: the existence of unsaturated native plant communities, empty niches, shifting trait optima of species as a result of environmental change and incomplete colonization–extinction processes following invasion. Future comparisons of functional trait differences between native and alien species should include assessment of the shapes of inter-specific trait distributions since these may differ even when the mean values of traits are similar for native and alien species. The infrequent application of such approaches may explain the limited generalizations regarding the drivers and consequences of plant invasions in plant communities.