Changes in multiple environmental factors additively enhance the dominance of an exotic plant with a novel trade‐off pattern

Abstract

Abstract Whether global changes impact native and exotic species differently is unclear, because the changes may favour both native and exotic species over competitors. Previous studies have mainly focused on the separate effects of different environmental changes, but plant communities are influenced by the changes in multiple environmental factors, and it is still unclear whether native and exotic species respond similar to the combined effects of these factors. We hypothesized that differences in interspecific trade‐offs between native and exotic species can lead to the dominance of exotic species when the species are simultaneously subjected to multiple environmental changes. Using coastal saltmarsh plant communities as the study system, we experimentally manipulated flooding and nutrient enrichment, examined the interspecific trade‐offs between competitiveness and stress tolerance for two native and one exotic species, and explored the combined effect of the two environmental changes on both native–native and native–exotic species interactions. We found that flooding and nutrient enrichment oppositely affected native–native species interactions but additively affected native–exotic species interactions. The two factors together resulted in no net change in the relative advantages between the two native species but enhanced the dominance of the exotic species over the native species. This disparity occurred because the exotic species was not subject to the interspecific trade‐off between competitiveness and stress tolerance that constrained the native species. Synthesis. Our results suggest that changes in multiple environmental factors favour exotic species because of evolutionary novel trade‐off patterns. Mechanisms underlying species coexistence in the invaded community such as interspecific trade‐offs need to be considered when future attempts are made to predict the effects of global changes on biological invasions.