Are exotic plants more abundant in the introduced versus native range?

Many invasion hypotheses postulate that introducing species to novel environments allows some organisms to escape population controls within the native range to attain higher abundance in the introduced range. However, introductions may also allow inherently successful species access to new regions where they may flourish without increasing in abundance. To examine these hypotheses, we randomly surveyed semi-arid grasslands in the native and two introduced ranges (12,000-21,000 km2 per range) to quantify local abundance (mean cover per occupied plot) and occurrence (percentage of 1-m2 plots occupied) for 20 plant introductions that included pest and non-pest species. For each of these metrics, we evaluated relationships between abundance in the introduced versus native range 1) across all species and 2) according to designated pest status in the introduced range. We predicted that if escape from population controls primarily explained invader success, then these species would be more...