Biology Reference
In-Depth Information
tive mechanism. For example, some studies have suggested that the most
pernicious invasive species are members of genera that do not occur in
the invaded region. A few examples include trees such as ailanthus, casua-
rina, Brazilian pepper, tamarisk, and Russian olive in North America and
various species of pines in South Africa (Rejmánek 1996a). Studies in
Hawaii, on the other hand, suggest that in most plant families invasive
species tend to belong to genera that are already present rather than new
genera (Daehler 2001). Whether this represents a consistent difference
between continental and insular regions is not yet clear.
Additional sets of statistically significant correlations involve the ten-
dency for invasive plants to have an extensive range in their native region
and to be invasive in more than one geographical region. In eastern
Canada, for example, Goodwin et al. (1999) studied 165 pairs of Euro-
pean plant species, one member of which had invaded eastern Canada and
one of which had not. They found that 70% of the Canadian invaders
could be predicted from their distribution in Europe. In an analysis of 235
species of alien woody plants that have become naturalized in North
America, Reichard and Hamilton (1997) found that invasiveness in other
regions was the most reliable predictor of whether or not a species would
be invasive in North America.
Biological features related to invasiveness for animals are similar to
those of plants in many ways. Ehrlich (1986) noted, for example, that inva-
sive animals tended to be have broad feeding habits, high adaptability to
physical conditions, short generation times, high genetic variability, and a
tendency for association with humans. Lodge (1993a) also noted that
invasive animals showed high dispersal rates, phenotypic plasticity, and
often asexual reproduction. For aquatic organisms, McMahon (2002)
found that Eurasian zebra mussels (
Dreissena polymorpha
) and Asian clams
(
Corbicula fluminea
) contrast sharply with native North American clams in
having extremely high fecundity, rapid growth, early maturity, and short
life span. Nonnative ants, particularly those with worker castes that fight
in competition with other ants, tend to be smaller-bodied than con-
generic native species (McGlynn 1999), although the benefit of small size
is not certain.
For introduced land bird species, Cassey (2002) found that habitat
generalism tended to favor establishment success, together with nonmi-
gratory behavior and lack of sexual dimorphism in plumage. Dietary and
nest site flexibility have also been related to establishment success of birds
introduced to islands (McLain et al. 1999).
