Post-invasion evolution of native plant populations: a test of biological resilience

Contemporary evolution may explain the success of some exotic plant invasions. However, the evolutionary response of recipient native plant populations to exotic invasion has received relatively little attention. Because plant populations are genetically variable, contemporary evolution may also occur in native populations following entry of invasive species. Previously, we documented molecular differences in native populations; here we extend these studies to evaluate growth of native species in a common garden experiment. We seek to determine if three populations of two native grass species (Hesperostipa comata and Sporobolus airoides) demonstrate evidence of contemporary evolution in response to invasion by Acroptilon repens. We obtained 50 genets of the two native grass species from communities long-invaded (25-80 years) by A. repens and from adjacent, noninvaded areas, and planted five transplants of each genet into two A. repens infestations (Laramie and Fort Steele, Wyoming, USA) to document their growth and survival. Cumulative differences between collections from invaded and noninvaded communities were species-specific. S. airoides displayed a consistent positive response to long-term coexistence with A. repens, whereas the performance of H. comata originating from invaded communities was not different from H. comata collected from noninvaded communities. In general, genets from invaded communities had fewer tillers than genets from noninvaded communities, but their relative tiller production (percent increase) was greater for genets from invaded communities at both field transplant sites for both grass species. Basal area increase and overall performance of collections from invaded and noninvaded communities of origin depended on transplant site and grass species. The results suggest that native species have the potential for adaptation to coexist with exotic invasives, although that potential may differ among species.