Environmental Engineering Reference
In-Depth Information
also a key driver of the rate of population growth and range expansion. Possession
of a persistent, dormant life-stage (e.g. long-lived seeds) may also increase a spe-
cies' establishment capacity in environments novel to it. Species that have specifi c
requirements for pollinators, dispersal agents, or other symbiotic organisms are
likely to be less invasive where those organisms are absent (Rejmánek
et al
.
2005).
Species with traits that facilitate rapid invasion are often the most di cult to
contain. For highly fecund species, a containment strategy may have to contend
with a strong capacity for population growth. E cient dispersal abilities increase
the probability the containment zones will be breached. Short generation times
will mean that, following such a breach, there will be only a narrow window of
opportunity in which to detect and eliminate new outbreaks before they in turn
become source populations. For species with broad ecological tolerances there will
be fewer spatial or temporal barriers to range expansion and population increase.
Characteristics that determine how readily individuals and populations of a spe-
cies can be detected also infl uence the feasibility of containing them (McNeeley
2005). Species that are cryptic during all, or part, of their life cycle may be more
di cult to contain than those that are more readily detected (e.g. Panetta and
Lawes 2003; Correll and Marvanek 2006).
Containment of invasive species will be less feasible in some environments and
landscapes than in others. In the case of terrestrial weeds, complex topography,
dense vegetation, and heterogeneous environments reduce the probability of
detecting new populations. Any environmental or landscape characteristics that
reduce accessibility increase the costs of containment. Some environments also
restrict the management options that are available. For example, the use of many
herbicides is not appropriate in wetland or riparian environments because of the
risk of those herbicides or their break-down products moving away from the target
site (e.g. Krutz
et al
.
2005).
Many aspects of the management regime imposed on a landscape can infl uence
the feasibility of containing an invading species. In general, it will be easier to con-
tain species invading landscapes that are intensively managed. In such situations,
detection and access are less likely to present major problems. Intensively used
landscapes tend to support higher human populations that may be in a better
position to provide the human, technological, and fi nancial resources required to
detect and treat an invasive species that has breached a designated containment
line. On the other hand, the higher human populations likely to be found in inten-
sively used landscapes may provide anthropogenic means of dispersing invasive
species (e.g. ants), and increase the social challenges to containment (van Schagen
et al
. 1994; Plowes 2007). Unless there is universal acknowledgement that a par-
ticular invasive species is a problem, there will be confl icting views on how import-
ant containment is. Community members or organizations that do not view the
species as a problem, whether for them or for the community as a whole, may fail
to comply with legislation or to cooperate in management actions designed to con-
tain the species. h ese issues are likely to be especially signifi cant for species that are
perceived to have benefi ts, as well as environmental costs.
