Inter- and intraspecific selection in alien plants: How population growth, functional traits and climate responses change with residence time

Abstract

Aim: When alien species are introduced to new ranges, climate or trait mismatches may initially constrain their population growth. However, inter- and intraspecific selection in the new environment should cause population growth rates to increase with residence time. Using a species-for-time approach, we test whether with increasing residence time (a) negative effects of climatic mismatches between the species’ new and native range on population growth weaken, and (b) functional traits converge towards values that maximize population growth in the new range. Location: Germany. Time period: 12,000 years BP to present. Major taxa studied: Forty-six plant species of the Asteraceae family. Methods: We set up a common-garden mesocosm-experiment using annual plant species with a wide range of residence times (7–12,000 years) and followed their population dynamics over 2 years. We calculated climatic distance between the common garden and the species’ native range. We also measured key functional traits of each species to analyse trait–demography relationships and test trait convergence with increasing residence time. Results: We found no support for the hypothesis that negative effects of climatic mismatches on population growth weaken with residence time. However, seed mass had a clear negative effect on population growth. As expected under such strong directional selection between or within species, increasing residence time led seed mass to converge to low values that increase population growth. Accordingly, population growth tended to increase with residence time. Main conclusions: We identify trait but not climatic mismatches as important constraints on population growth of invaders. Understanding how inter- and intraspecific selection shapes functional traits of alien species should improve the predictability of future invasions and help understanding of limits to the population growth and spread of invaders already present. In a broader context, this study contributes to the conceptual integration of invasion biology with community, functional and population ecology.