Biology Reference
In-Depth Information
distribution and abundance of an invasive species, including the long-term results
of any control efforts on invasive species and the effects of changing climates, land
use, and trade and transportation through time. In this chapter, we will review the
important components involved in predicting spread rates, review the current com-
pared with the needed state of data collection and data analysis techniques, and
examine strategies to effectively control invasive species in the long term.
6.2 Forecasting Considerations
Forecasts of invasive species spread rates can aid management activities at many
different levels. At large scales such as national or state/province equivalents, they
may assist high level managers with the distribution of limited resources for pre-
vention and control efforts. Forecasts may also provide “watch lists” to manage-
ment units of species that may invade their area. A specified year or time period of
expected arrival associated with these predictions narrows down the number of spe-
cies for resource managers and their helpers to be especially vigilant for at any
given time. Additionally, species that are predicted to spread more rapidly than oth-
ers may require a much quicker response for containment or eradication than a
species that spreads very slowly with low propagule production over decades. For
example, a plant species producing many small, windblown seeds may quickly
infest large areas. Individual plant characteristics like this example may have a
great effect on spread rates along with the more general factors discussed in more
detail below. Understanding the spread of a species over time through a local area
can aid in setting priorities for control and eradication efforts among various spe-
cies and for neighboring small infestations of a particular species. When generating
these invasion forecasts, there are several different concepts that should be
considered.
6.2.1
Time Since Establishment
A general factor that should be included with any invasive species spread model is
the time since invasion, or at least how far along the invasion process the species
has proceeded at the particular location being examined. In the case of multiple
introductions, the invasion stage may vary at different focal points and may have an
accelerated response compared with a single introduction. These multiple introduc-
tions are similar to anthropogenic long distance dispersal, which can cause an
accelerated expansion rate A species early in the invasion process may not have had
the opportunity to establish in all locations with environmental conditions within its
“ecological envelope” (e.g., locations with suitable habitat). A species that is near-
ing the final stages of invasion, having maximized its potential range, may be
treated more like a native species in development and interpretation of models of
