Biology Reference
In-Depth Information
Table 6.2
Essential factors, in addition to species-specific characteristics, to consider when
developing any forecast for the spread of invasive species.
Type
Description
Invasion stage
The stage in the invasion process - initial introduction,
establishment, spread, naturalized; lag effects are important in
relation to the stage
Residence time
Time since initial introduction, which interacts with other factors
to influence spread through lag times
Propagule pressure
Number of individuals originally introduced and the rate of
subsequent introductions to a particular location
Vectors or pathways and
barriers to invasion
Mechanisms of dispersal for spread or barriers that prevent spread;
mechanisms responsible for moving the species long distances
are especially important
Environmental stochas-
ticity
Differences in the environment through time can alter spread rates
(a component of lag times)
Long-distance dispersal Dispersal events driving the range expansion of a species
Allee effects A relationship between population growth and density of
individuals that is species specific and can influence rate of
spread (a component of lag times)
All of these factors are rarely if ever incorporated into forecasting models, but are necessary
components for a well-developed forecast
6.4 Managing Invasive Species Spread in Long Term
6.4.1 Lessons for Control Prioritization
Forecasts over time could potentially help make control and eradication efforts
more cost effective by informing prioritization of management efforts based on
potential impact of various locations. Spatial considerations such as distance from
source populations are important in determining where control efforts should be
carried out. At a local scale, forecasts could be used to prioritize patches of invasion
on the basis of predicted patch size and therefore impact (Fig. 6.2). For example,
there are two small patches of an invasive species in a management unit, only one
of which can be affordably eradicated. A local scale spread model for the species
predicts that one will persist at very low levels and not spread to the surrounding
area. The other is predicted to become very dense and act as a source for other
populations. The second patch therefore would be the one on which to focus control
efforts. Another consideration is the original source of an infestation. If new prop-
agules are continually arriving, control efforts would be more effective if the source
was also controlled. Without the input from temporal predictions, the resource
manager would have to randomly choose or divide resources between locations,
potentially not being able to effectively control the spread of the species in their
area as well as they would with temporal predictions.
