Biology Reference
In-Depth Information
compellingly justified by so cavalier an argument. So it is with alien species. There
is nothing remotely natural about the Homogocene, and arguments that pretend that
this is the case are contrary to the evidence. Consequently, this topic is written from
the viewpoint that alien invasions - including those by reptiles and amphibians -
are a serious ecological threat that demands attention and remediation.
The Invasion Process
In the past 20 years or so considerable scientific attention has been directed to
understanding invasive species biology and how a species becomes invasive.
Conceptually, the invasion process involves three stages: transport and release of
the organism to a novel geographic area, establishment of a population in the new
area, and expansion of the original population to fill ecological space beyond its
point of entry. The biological and social factors that favor success in any one of
these steps may not be the same as those favoring success in others (cf. Duncan
et al., 2003). For example, successful transport may rely on the ability of a species
to survive food deprivation for long periods or to tolerate harsh environmental con-
ditions. Some perceived human benefit from the species, of course, also weighs
heavily in the choice of those species that are deliberately introduced. Once arrived
in the new habitat, population establishment requires that the climate be survivable,
that appropriate food be available, and that reproduction be possible. Once estab-
lished, rapid expansion may rely on access to food sources underutilized by native
species, ability to avoid resident predators, or absence of debilitating disease organisms.
As a consequence of these varied requirements, many organisms may fail to survive
transport, those that do may fail to establish populations, and many that initially
establish populations may fail to persist or to expand their ranges. To understand
invasions, then, requires knowledge of how all three stages in the process are suc-
cessfully negotiated by the invading species.
Transport
A host of pathways serves to introduce alien species to new environments.
Unintentional introductions largely result from species hitch-hiking rides in cargo
or on the vehicles used in transport. Examples include brown treesnakes ( Boiga
irregularis ) being transported in wheel wells of aircraft, geckos stowing away in a
variety of cargo shipments or the containers used to package cargo, plankton
moved in the ballast water of ships, sessile marine invertebrates riding on the hulls
of ships, and insects infesting grain shipments. Also included in this category are
disease-causing agents moving about on infected humans (e.g., AIDS, malaria),
their domesticated animals (e.g., rinderpest, avian influenza), or other vectors (e.g.,
dengue in mosquitoes travelling in used tires, cholera travelling in ballast water).
Search WWH ::




Custom Search