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

Abstract

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 Á80 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.

Impact of Acroptilon repens on co-occurring native plants is greater in the invader’s non-native range

“…Their results indicated that a small portion of loci may be linked to genes undergoing selection caused by Acroptilon invasion. In a second experiment, S. airoides genets collected from old Acroptilon patches showed consistently greater growth when transplanted into other patches of Acroptilon than genets collected patches with no Acroptilon, suggesting that some native species have the potential for adaptation to coexist with this invader (Mealor and Hild 2007; also see Callaway et al 2005).…”

Phenotypes of Two Generations of Sporobolus airoides Seedlings Derived from Acroptilon repens‐invaded and Non‐invaded Grass Populations

“…Remnant native grasses remaining following invasions are not normally included in native seed collections. But, for reasons argued above and elsewhere (Mealor et al 2004; Mealor & Hild 2006, 2007), we suggest that remnant subpopulations may provide alternative seed sources to establish desirable native species communities with increased resistance against exotic invaders (Leger 2008).…”

“…The length of knapweed presence for each site was estimated to be from 40 to 75 years based on published literature and herbarium records (Mealor & Hild 2006). Invaded and non‐invaded communities were delineated by a clear absence of A. repens in the non‐invaded type, and were separated by less than 20 m at each location (Mealor & Hild 2007). We randomly collected 10 maternal plants from each community type at each location by hand‐excavating approximately 25‐cm diameter plant portions, which were transported to greenhouse facilities at the University of Wyoming, Laramie, Wyoming, U.S.A.…”

“…Just as genetic adaptations are thought to increase the establishment and invasiveness of exotic species, natural selection may promote adaptive responses of remnant native species to invasions (Carroll 2007). Remnant native plants may provide desirable seed sources for native plant production and restoration because populations under selective pressures associated with invasions may have developed an increased resilience against invasive species (Lesica & Allendorf 1999; Mealor & Hild 2007).…”

“…This research builds on prior work that examined the competitiveness of mature remnant native plants (Mealor & Hild 2007; Ferrero‐Serrano et al 2010). However, documenting phenotypic traits throughout a plant's life, from seed to maturity, will help us understand the influence of weed invasions on the restoration potential of invaded native grass populations.…”