Biology Reference
In-Depth Information
of the same taxa could lead to adaptive evolution in cases where the species was
intentionally introduced multiple times (resulting in a diverse gene pool), and that
this process would occur only after a lag period. Given the history of swallow-wort
introduction and invasion, and evidence of hybridization occurring between two
Vincetoxicum
species, we suggest that there is a high potential for occurrence of
rapid evolutionary changes among introduced swallow-worts (DiTommaso et al.
2005b; Lauvanger and Borgen 1998).
There is also evidence that the rapid evolution of plasticity for ecologically advanta-
geous traits is relatively common among invasive species, and that this may partially
explain the success of many invasive species only after an initial lag time during which
necessary evolutionary adjustments have occurred (Pigliucci 2005; Richards et al.
2006). The potential roles of trait plasticity in the invasiveness of the two swallow-wort
species are of great interest given reports of wide variation in reproductive and phe-
nological traits among invasive swallow-wort populations (DiTommaso et al. 2005b;
Lawlor 2000; Sheeley 1992; St. Denis and Cappuccino 2004).
Nevo (1988) and Nevo et al. (1984) found that plant species tend to be more
genetically polymorphic if they occur in broader climatic, ecological, or biotic
spectra, both at the macro- and microgeographic scale. Agrawal (2001) predicted
that species whose phenotypic traits are exposed to (and thus respond to) larger
ranges of environmental stimuli will be more likely to influence both the ecology
and perhaps evolution of that species' interactions in novel habitats. Our prelimi-
nary work characterizing genetic diversity levels amongst PSW and BSW popula-
tions throughout New York state has suggested that while the two species are
genetically distinct, intraspecies genetic diversity is actually relatively low
(Douglass 2008). The further determination of molecular patterns and degrees of
adaptive morphological variation in introduced swallow-wort populations should
be a research priority as the species clearly display strong abilities to acclimatize to
diverse environments.
13.9 Conclusions
It has been proposed that it is possible to predict the invasiveness of particular plant
species from some life history traits, including the capacity to reproduce vegeta-
tively, seed size and volume of production, and the persistence of the seed bank,
among others (Myers and Bazely 2003; Rejmanek and Richardson 1996). Pale and
BSWs are characterized by many of these traits, arguably making them archetypal
invasive plants. While we do not currently fully understand the role of vegetative
reproduction in the rapid spread of the swallow-worts, we are gaining information
related to their physiology, ecology, and invasiveness (DiTommaso et al. 2005b;
Weston et al. 2005). The apparent ability of these species to become invasive in
many locations in New York state indicates that swallow-worts have an enhanced
propensity toward establishing in and becoming invasive in novel habitats that are
outside of their currently described range (Lockwood et al. 2007).
