Biology Reference
In-Depth Information
probably the most reasonable management objectives. The likelihood of success for
limiting further spread and reducing existing populations will depend on the avail-
ability and effectiveness of containment methods and size of existing populations.
Data on trends in abundance and distribution and dispersal capability can help
distinguish species that are spreading rapidly from those with slower spread rates.
Although the general categories of information on species in the spread stage are
the same as those in the establishment stage, the specific information that is of most
use is generally different (Table 2.1). Information on management feasibility and
distribution and abundance are more important than at other phases. Information
on impacts can still be useful for prioritizing species in the spread phase, but it is
more focused on actual impacts that have been observed than on the potential to
cause future impacts. Biogeographic information is not particularly helpful at this
phase because it should already be apparent which biogeographic regions (e.g.
habitat types) are being invaded by the species.
2.4.3.2 Information for Prioritizing Sites
There are two main categories of information to collect when prioritizing sites: (1)
susceptibility to invasion, and (2) the conservation value of the site (Table 2.3).
Management feasibility is another consideration, but of lesser importance.
Predicting the susceptibility of vegetation communities to invasion has long
been an active area of research (Rejmanek et al. 2005). Success of predictions for
general patterns has been elusive, but predictions are often reliable only when done
at local scales. Besides basic ecological information on nonnative species and land
use within the area of interest (intrinsic factors; Table 2.2), landscape configuration
and characteristics are also important (extrinsic factors; Table 2.2). This is because
invasive species may initially spread from neighboring lands. Attributes at the land-
scape scale should also be considered when prioritizing sites, especially patchiness
of vegetation communities (some communities are more prone to invasion caused
by edge effects; e.g., grasslands) and corridors connecting vegetation types to par-
ticular sites. Conservation value includes information on local hotspots of native
diversity, endemism, and threatened and endangered species, as well as other cul-
tural or recreational site values.
2.4.4 Prioritized Monitoring Plan
Prioritization can help further reduce the area identified for monitoring in a general-
ized monitoring plan (Fig. 2.1), and thus increase monitoring efficiency (Fig. 2.4).
The specific approach will depend on whether the prioritization was developed for
colonizing species, species established in an area but not yet spreading, or species
currently spreading through an area. Preventing colonization will require monitoring
vectors and pathways to the site, as well as areas where the species is likely to
