Invasiveness in wetland plants in temperate North America

Abstract

The spread of invasive taxa, including Lythrum salicaria, Typha X glauca, Myriophyltum spicatum, Phalaris arundinacea, and Phragmites australis, has dramatically changed the vegetation of many wetlands of North America. Three theories have been advanced to explain the nature of plant invasiveness. Aggressive growth during geographic expansion could result because 1) growth is more favorable under new environmental conditions than those of resident locales (environmental constraints hypothesis); 2) herbivores may be absent in the new locale, resulting in selection of genotypes with improved competitive ability and reduced allocation to herbivore defenses (evolution of increased competitive ability hypothesis); and 3) interspecific hybridization occurred between a new taxon and one existing in an area, resulting in novel phenotypes with selective advantages in disturbed sites or phenotypes that can grow under conditions not favorable for either parent (introgression/hybrid speciation hypothesis). A review of published literature found few studies that compare the growth and dynamics of invasive populations in their new range versus those in historic ranges. However, there is evidence that hydrologic alterations could facilitate invasions by Typha × glauca and Phalaris arundinacea and that increased salimty promoted spread of Typha angustifolia (parental taxon) and Phragmites australis, The potential for reduced herbivory causing aggressive growth is greatest for Lythrum salicaria. Introgressive hybridization is potentially a cause of invasiveness for all five species but has been established only for Typha × glauca and Lythrum salicaria.

Evidence of hybridity in invasive watermilfoil ( Myriophyllum ) populations

“…Cycle sequencing of ITS used combinations of the ITS-2, ITS-3, and ITS-4 (23) primers. Cycle sequencing of only the ITS-2 region was performed for the majority of M. spicatum and M. sibiricum specimens because of the ample variable sites (6) found in this region to differentiate the taxa, although entire ITS sequences were obtained from all of the cloned hybrids. The 5Ј-trnK intron was sequenced by using trnK-3914F and a newly developed Haloragaceae specific primer, ''360F'' (5Ј-TATGAATGTGTAGAAGAAG).…”

“…Introductions into new ''benign'' environments are often assumed to provide conditions favorable for an introduced species to thrive, but experimental evidence in support of this assumption has not been forthcoming (5). Arguably, a lack of associated herbivores or other natural controls also may impart advantages to nonindigenous species over native plant species whose populations are regulated by competition and predation (4,6).…”

“…The potential for hybridization between nonindigenous and native species has also raised concerns, due mainly to introgression, which can cause extirpation of native species through gene contamination (6)(7)(8). Another possible outcome of hybridization is heterosis, or ''hybrid vigor,'' which is often expressed as high vegetative vigor in some progeny (9,10).…”

Marsh and Riparian Habitat Compensation in the Fraser River Estuary: A Guide for Managers and Practitioners

“…Disturbed habitats are more susceptible to the colonization of exotic and invasive species than intact habitats. 33,34 Suppression of Lyngbye's sedge in compensation sites may begin at the time of site creation, when disturbed soil is most available for colonization by invasive species. If unmanaged, several exotic and invasive species may compete with and displace native plant communities over time.…”

Fen Management and Research Perspectives: An Overview

“…While these problems might be alleviated by the reconnection of dispersal corridors (Taylor et al 1993), higher amounts of dispersal between these disconnected wetlands could contribute to more opportunities for an invasion of exotic species in North America, where invasive species in wetlands are a major problem (Galatowitsch et al 1999). …”