Risk assessment of invasive species - Invasive Species Management - page 25

Table 2.2 Some general traits of successful invaders adapted and summarized
from the studies cited in the text.

Trait Example

1. Exceptional dispersal characteristics
(e.g. by wing, water, animals, zoospores,
pelagic stages, etc.)

Wind-blown seed of dandelions, many
bird species carrying West Nile virus.

2. Rapid establishment and growth to
reproductive age

Mediterranean woody angiosperms,
annual grasses in California,
New Zealand mud snail.

3. Few natural enemies or predators in
the new environment

Mongoose in Hawaii, brown treesnake
in Guam.

4. Ability to sequester underused
resources

Shade-tolerant Japanese honeysuckle,
zebra mussels.

5. Copious reproduction All organisms mentioned above.

selected regions have had more predictive success. Species' life history traits also
are important determinants of invasion potential (Rejmánek 1996; Rejmánek and
Richardson 1996; Reichard and Hamilton 1997).
Unfortunately, obscure species traits may be particularly important for some
invaders. For example, European wild oats has awns that self-bury, allowing greater
resilience to wildfi re with a plentiful seed bank. Plant pathogens such as white pine
blister rust had the plasticity to fi nd alternate hosts and target species after arrival
in the United States in the early 1900s. h us, there are many exceptions to the
generalizations in Table 2.2. Not all invaders have all the successful traits, and some
species have many of the successful traits, but are not good invaders, at least not yet!
Residence time (i.e. the time since the species was introduced) may be an import-
ant 'attribute' of a species indirectly aff ecting genetic diversity or adaptations of the
species (Wilson et al . 2007).

2.2.2 Matching species traits to suitable habitats
All species require suitable habitats to establish, reproduce, and spread (Fox and
Fox 1986; Panetta and Mitchell 1991; Hobbs and Huenneke 1992). So, invasion
also depends on environmental characteristics that may predispose a habitat to
invasion (Table 2.3) (Tyser 1992; Robinson et al . 1995; Lee 2001). As with species
characteristics, generalizations of habitat vulnerability to invasion have also been
slow to emerge (Usher 1988; Lodge 1993; Lonsdale 1999).
h e quantity and quality of available resources also may be important in assess-
ing the vulnerability of an ecosystem to invasion. In some cases, an invading species
may take advantage of under-used resources in an ecosystem. For example, Bromus
tectorum (cheatgrass) in some regions is said to benefi t from fall or winter precipita-
tion, while many native plant species are senescent (Bates et al . 2006). In addition,