Light intensity and seed density differentially affect the establishment, survival, and biomass of an exotic invader and three species of native competitors

Abstract

Understanding how invasive and native plant species respond to their environment is essential for explaining and managing plant invasions in changing ecosystems. Light limitation and density-dependent interactions affect plant performance, but few studies have experimentally evaluated the effects of these factors on invasive and native neighbors simultaneously. Our objective was to test the hypothesis that light limitation and density-dependent interference are critical factors that influence the performance of the invasive species Bromus madritensis ssp. rubens (“B. rubens”) and three native species that commonly compete with B. rubens in North American drylands. In a full-factorial experiment, we examined the effects of (a) light limitation, (b) increasing B. rubens seed density, and (c) increasing native seed density on the establishment, survival, and biomass of each study species over a 12-week growing period in a controlled greenhouse. Light limitation reduced at least one performance metric (establishment, survival, or biomass) for all species. Increasing B. rubens seed density had no intraspecific effect on its own performance but had variable and species-specific negative effects on natives. Increasing native seed density reduced B. rubens establishment, survival, and biomass but had variable and species-specific effects on the natives themselves. These findings suggest that light intensity and density-dependent interactions can strongly but differentially influence the establishment, survival, and biomass of an important subset of invasive and native species in North American drylands. Evaluating multiple performance metrics at the species level is essential for understanding how invasive and native neighbors respond to environmental variation in changing dryland ecosystems.