Global meta-analysis of trait consistency of non-native plants between their native and introduced areas
Invasion biologists have made an extensive exploration of ways to identify the characteristic traits of invasive plants based on the assumption that plant attributes remain similar when plants become invasive. However, this assumption needs to be critically evaluated when predicting successful future introductions.
Using a global database of plant functional traits (i.e. specific leaf area, maximum canopy height and individual seed mass) encompassing 129 different species three questions were evaluated using a meta-analytical approach. (1) Do traits of introduced aliens change between native and introduced areas? (2) Do the responses show directionality, indicating that traits of aliens are either consistently higher or lower in their introduced range? (3) Are there smaller differences in species between native and introduced areas (within-species multitrait variation) than between two random species (between-species multitrait variability)?
Mean trait differences (measured as log-response ratios) between native and introduced (invasive + naturalized), native and naturalized, or native and invasive areas showed no significant differences across evaluated species, even after controlling for invasion status and growth form. This pattern was the result of aliens showing both higher (Alienarea > Nativearea) and lower (Alienarea < Nativearea) trait values in their introduced areas. Furthermore, multitrait differences between populations in the native and introduced areas were significantly less than differences in the mean trait composition between species (as determined by contrast with two different null models).
The similarity of evaluated traits between areas, in combination with a smaller within-species than among-species trait variability, are fundamental results for conservation and nature management efforts. The results presented in this study validate the assumption that mean trait measurements in the native areas are likely to be reasonably representative of trait mean values in the invaded areas, and support the use of trait-based prediction methods to evaluate the potential of an introduced plant to become established.