Biology Reference
In-Depth Information
potential range based on matching climatic variables from its native range is
increasingly common (e.g., Peterson and Vieglais, 2001; Thuiller et al., 2005;
Ficetola et al., 2007a). Second, the alien must have sufficient resources available to
complete its life cycle. At a minimum, this means sufficient food, living space,
habitat for growth and reproduction, and whatever other biotic factors, such as
pollinators, may be required. This is thought to be made easier if the intruder pos-
sesses adaptive features lacking in the biota of its newly inhabited range, thus
allowing it to pursue its way of life unhindered by close competition. Third, favo-
rability of the introduced range may also be increased by the absence of predators,
parasites, and disease organisms from the alien's native range. Leaving these enemies
behind often gives an alien species a considerable competitive advantage over the
natives it meets in its new home.
It is also clear that propagule pressure - the number of individuals released into a
new area - is an important determinant of successful establishment. Those species
that have been released more often, at more sites, or in greater numbers tend to estab-
lish more successfully than those that do not (M. Williamson, 1996, 1999; Duncan
et al., 2001, 2003; Forsyth and Duncan, 2001; Kolar and Lodge, 2001; Bomford and
Glover, 2004; Forsyth et al., 2004; Lockwood et al., 2005; Rejmánek et al., 2005;
Caley and Kuhnert, 2006; Jeschke and Strayer, 2006; Hayes and Barry, 2008),
although it can take many introductions to make this pattern statistically apparent
(e.g., Ruesink, 2005; Bomford et al., in press). The larger the number of individuals
released at a given site, the lower the chance of stochastic extinction (extinction due
to bad luck randomly happening to strike all released individuals). Similarly, releases
at more sites increase the odds that at least one population will survive by effectively
sampling the environment for habitat most suitable to the introduced alien. Finally, a
larger number of independent releases will likely sample a greater representation of
genetic diversity from within the introduced species, providing greater genetic and
(potentially) phenotypic variation with which to meet the ecological and evolutionary
challenges of the new environment (Lockwood et al., 2005).
Unsurprisingly, life-history and behavioral characteristics of the introduced
species can be important in determining establishing success (Reichard and
Hamilton, 1997; Sol and Lefebvre, 2000; Duncan et al., 2001; Kolar and Lodge,
2001, 2002; Cassey, 2002; Cassey et al., 2004; Forsyth et al., 2004; Rejmánek
et al., 2005; Ruesink, 2005; Jeschke and Strayer, 2006; Thuiller et al., 2006; Hayes
and Barry, 2008). Such attributes vary among taxa and may even vary within the
same taxon, either because different genotypic samples are involved or because
different environments may induce different phenotypic effects. This idiosyncrasy
again limits the taxonomic scope across which we may identify biological traits
predictive of establishment success. This makes attaining useful generalizations for
a broad array of taxa a laborious undertaking.
One of the most useful predictors of establishment success is whether a species
has already successfully established somewhere else (Reichard and Hamilton,
1997; M. Williamson, 1999; Duncan et al., 2001; Forsyth et al., 2004; Caley and
Kuhnert, 2006; Hayes and Barry, 2008). This is obviously not a very refined tool
for predictive use. It doesn't carefully discriminate among introductions to different
