Environmental Engineering Reference
In-Depth Information
What do we need to know to understand, estimate, and predict the risks asso-
ciated with invasive biological organisms? Risk assessment for biological organ-
isms requires information on the invading species, vulnerability of habitats to
invasion, modelled information on current and potential distributions, and
the costs associated with containing (or failing to contain) harmful species
(Table 2.1).
We summarize information needs and a general strategy for risk assessment for
invasive species based on the ultimate risk assessment challenge. h e most import-
ant aspect of the process is that it is an iterative approach, improving risk assess-
ments as new information and modelling become available. h e initial process
requires:
•
Detailed information on invading species traits.
•
Matching those traits to suitable habitats for the invading species.
•
Estimating exposure (or propagule pressure).
•
Surveys of current distribution and abundance.
•
An understanding of data completeness.
•
Estimates of the 'potential' distribution and abundance of the species.
•
Estimates of the potential rate of spread (and pathways, corridors, and barriers
to invasion).
h e probable risks, impacts, and costs of the invading species to the environ-
•
ment, economy, and human health.
h e containment potential, costs, and opportunity costs.
•
•
h e legal mandates and social considerations in containing and controlling
the species (Table 2.1).
Some species are better invaders than others, and classifying potentially harm-
ful species is our fi rst di
cult task in risk assessment of biological hazards. Plant
biologists have long tried to identify an 'ideal' invader species based on traits of
successfully colonizing species (Table 2.2) (Bazzaz 1986; Roy 1990; h ompson
et al
. 1995). For example, Grotkopp and Rejmánek (2007) clearly showed that
high seedling relative growth rate and specifi c leaf area are traits of invasive woody
angiosperm species in Mediterranean climates. Many general traits (Baker 1965;
Lodge 1993) and strategies (Grime 1974; Newsome and Noble 1986) are associ-
ated somewhat with increased invasion potential (Table 2.2), but an exclusive set
of invader traits has not emerged (Newsome and Noble 1986; Crawley 1987; Roy
1990), hampering the ability to predict responses of individual species (Hobbs and
Humphries 1995; Reichard and Hamilton 1997; Lee 2001). Sometimes, species,
taxonomic, and behavioural traits do help identify and rank invaders (Panetta and
Mitchell 1991; Lee 2001). h is is based on observations that particular species in
