Invasive species are typically viewed as a large threat to biodiversity. However, current literature argues that invasive species, specifically plant invaders, rarely cause regional species extinctions and can often increase overall species richness. We propose that this discrepancy may be caused by scale dependent effects of invasive species on native communities, which can be observed through Species-Area Relationships (SARs). We examined how three prominent plant invaders in disparate ecosystems across the United States (i.e., Hawaii, Missouri, and Florida) affect the slope (Z) (species accumulation) of the native species SAR. 

Results/Conclusions

Paired t-tests revealed that across ecosystems, invasive species significantly increased the slope (Z) of native species SARs. This change in the scaling of species richness caused differential declines in richness at different spatial scales; invasive species had larger effects on native species-richness at small (1m²) than large (500m²) scales. We suggest that increases in Z are caused by invaders increasing the evenness of native communities’ Species-Abundance Distribution. Our results show how plant invaders can dramatically affect species richness despite few extinctions at large spatial scales.