Biology Reference
In-Depth Information
Intentional introductions occur primarily because a species is perceived to provide
an amenity or use value to humans. Under this category fall introductions for
use as pet animals, furs, human or livestock food, horticulture, and biocontrol of
pests. Included as well are introductions and releases undertaken by individuals
simply because they like a particular species and wish to be able to see it in their
surroundings. As a rule, some taxonomic groups, such as marine invertebrates,
insects, and landsnails are largely dispersed via unintentional pathways. Others,
primarily plants, fish, birds, and mammals have largely been intentionally
dispersed by humans. As I will demonstrate later, reptiles and amphibians are
somewhat unusual in that they are transported via a diversity of intentional and
unintentional pathways.
In considering intentional introductions, human selectivity ensures that those
species introduced do not represent a random selection of all available species.
Instead, species chosen for introduction can be biased taxonomically, geographi-
cally, and in having particular characteristics such as large body size, tasty flesh, or
large population sizes (Blackburn and Duncan, 2001a; Duncan et al., 2003). In
addition, they are often especially hardy, an attribute of obvious importance if a
species is to be used for a purpose. Although this is intuitively obvious, the phe-
nomenon has been quantified for few taxa. Recipient areas can also vary in being
primarily islands (Blackburn and Duncan, 2001a; Kraus, 2003c) or continents
(Kraus, 2003c), depending on the taxon in question.
Establishment
The naturalization process - the means by which a species establishes a reproducing
population once transported to a new region - is not yet understood in great detail.
Ideally, we would like to be able to learn enough to predict with reasonable
certainty how likely a particular alien species is to naturalize in a particular area
should it be introduced. But the particularities of both species and location that may
be involved in any given introduction make generalization across all introductions
difficult. This is because establishment success results from the interaction of the
singular combination of biotic and abiotic needs of a species with the particular set
of environmental conditions at the receiving location. Ideally, ability to predict nat-
uralization success would allow us to prohibit importation of species deemed at
high risk of establishment. Although we have not yet reached that point, several
important generalities are becoming apparent.
First, it is important that the newly attained region provide a favorable environ-
ment. Logically, the climate must be sufficiently similar to that in the native range
that a species' physiological tolerance is not exceeded. Consequently, climate
matching has repeatedly been found to be an important predictor of establishment
success (Blackburn and Duncan, 2001b; Duncan et al., 2001, 2003; Bomford and
Glover, 2004; Forsyth et al., 2004; Hayes and Barry, 2008). The importance of cli-
mate is sufficiently uncontroversial that modeling an alien species' anticipated
