LAUSR

Abstract Invader success might depend on both nutrient availability and species richness of the resident community. Here, we combine these ideas in a single experiment, testing whether the Fluctuating resource and biotic resistance hypotheses might be contingent upon one another. The fluctuating resource hypothesis proposes that resource fluctuation might facilitate the successful invasion of exotic plants if invaders are better than natives at taking advantage of resource pulses. The biotic resistance hypothesis proposed that more species rich communities might be more resistant to invasion, due to greater competition for resources with greater native richness. Here, we use an experiment with the invader, Chromolaena odorata in 315 artificial communities with resident plants from native and non-native ranges. We found that resident origin, nutrient treatment and species richness of artificial community have significant effects on invasion success of C. odorata. The effect of nutrient fluctuation on invasion success was contingent on resident origin (native vs. non-native range), and this effect was weaker in more species rich communities. In addition, the invasion success of C. odorata was negatively related with biomass of resident plants, suggesting competition as a mechanism governing invader success. Our results suggest a novel twist on the fluctuating resource hypothesis: fluctuating resources may favor invaders more in species poor communities of non-native origin. This also suggests that competition for fluctuating resources may be one mechanism governing biotic resistance because the effects of richness were greater when resources were fluctuating. Our results suggest that the fluctuating resource hypothesis will apply only to resident communities with lower resource acquisition strategies, relative to the invader.