Global resource acquisition patterns of invasive and native plant species do not hold at the regional scale in Mediterranean type ecosystems

Abstract

Invasive species may outperform native species by acquiring more resources or by efficiently using limited resources. Studies comparing leaf traits as a metric of carbon capture strategies in native and invasive species have come to different conclusions. Some studies suggest that invasive species are better at acquiring resources, but that native and invasive species use resources similarly. Other studies have found that native and invasive species differ in resource use efficiency, which implies different biochemical or physiological mechanisms of carbon capture. To resolve this debate, we examined relationships among four leaf traits (photosynthetic rate, specific leaf area, foliar nitrogen, foliar phosphorus) in co-occurring native and invasive species from eight plant communities across five Mediterranean-climate ecosystems. We performed standardized major axis regression for all trait combinations within and across sites, testing for slope homogeneity and shifts in elevation (y-intercept) or along a common slope between species groups. Across the global dataset, native and invasive species had similar carbon capture strategies (i.e., similar slopes), with invasive species occupying a position of greater resource acquisition. However, these patterns did not hold when regions were analyzed individually. Regional differences may be driven by differences in life form between native and invasive species, and variation in soil resource availability among regions. Our context-dependent results reveal not only that management of invasive species will differ across regions but also that global comparisons of invasive and native species can be misleading.