Christine S. Sheppard and Viktoria Ferenc
Institute of Landscape and Plant Ecology, University of Hohenheim, 70593 Stuttgart, Germany
Although conservation managers usually have to deal with multiple invaders that co-occur in native ecosystems, research to date has concentrated onstudying single highly invasive species. Consequently, this study aims to better understand the interactions among co-occurring alien plants. Specifically, we aim to determine how relative performance in a mixture (compared to growing alone and growing in intraspecific competition) depends on phylogenetic relatedness and similarity in functional traits.
We investigated the interactions among 18–20 alien annual plant species in Germany belonging to six to nine families using two multi-species common garden experiments, where plant individuals were grown in all pairwise species combinations. We measured growth, reproductive output and functional traits of the species, and determined phylogenetic and multivariate trait distances between target and neighbour individuals as well as individual trait hierarchies between pairs (using specific leaf area, maximum height, seed mass, root:shoot ratio, and flowering onset).
Across the 153–170 interspecific species combinations, individuals equally often experienced higher intraspecific or interspecific competition, with competitive responses varying greatly depending on the species. Facilitation (i.e. growing better in a mixture than alone) was rare, but mostly occurred when growing with a leguminous alien neighbour. Overall, hierarchical trait differences related to competitive ability were more important than niche differences (described by phylogenetic or multivariate trait distance) in determining the performance of co-occurring alien plants. Specifically, growth and seed production always increased when an alien species was taller compared to its co-occurring alien neighbour, whereas the effects of specific leaf area, seed mass, root:shoot ratio, and flowering onset depended on the performance measure. A better understanding on the interaction type and strength among multiple plant invaders is crucial to determine appropriate management actions as well as contribute to the ecological theory of community assembly.
Sheppard C. S. (2019) Relative performance of co-occurring alien plant invaders depends on traits related to competitive ability more than niche differences. Biol. Invas. 21: 1101–1114.