Biology Reference
In-Depth Information
these studies reflected rapid evolutionary changes by alien species—
organisms that had invaded or been introduced to new geographical areas.
The risks of unexpected evolutionary responses of alien species have
been increased by the rapidly expanding technology of genetic engineer-
ing.This is particularly true for genes that confer tolerance by crop species
and other “beneficial” organisms to herbicides or other pesticides, or that
confer systemic resistance to pests or diseases.The majority of these genet-
ically transformed species possess close relatives that are cropland weeds or
wild ancestral species with the potential to evolve weed races. The possi-
bility of escape of such genes via rapid evolutionary change demands the
utmost caution in their introduction to open agricultural systems.
Appreciation is also growing that evolutionary change occurs within
a community context, with change in individual species both being influ-
enced by many other species and having impacts on other aspects of the
community and ecosystem. This appreciation has led some to propose
community genetics as a new subfield of science (Neuhauser et al. 2003).
Whether or not such a branch deserves formal recognition, the fact is that
rapid evolutionary change involving alien species and the natives with
which they interact is proceeding on a very complex and influential eco-
logical stage.
Adaptation of Alien Species for Dispersal
Dispersal is a basic life history process for all organisms and one of cen-
tral importance to alien species. All species possess a life history stage—
spore, seed, egg, larva, or mature organism—that is adapted in some way
for transport by wind or water currents, attachment to animal carriers, or
active locomotion to sites that may offer suitable habitat. Plants and ani-
mals adapted to ephemeral or disturbed habitats have long been known
for their ability to disperse widely and colonize new, often isolated sites.
During human evolution, such species have proven to be well adapted to
the habitats created by human activity. Many have followed humans as
they migrated to new areas and often refined their life history traits to
take advantage of humans, both as creators of habitat and as agents of dis-
persal. Such species are preadapted to spreading rapidly once they have
been introduced to a new geographical region.
Many species have taken advantage of wheeled vehicles, seagoing
ships, and airplanes as agents of transport, enabling them to cross major
geographical barriers. Many of these species, especially plants, have been
carried deliberately to new regions (see, e.g., Mack and Erneberg 2002),
but others have hitchhiked. Modern systems of travel and commerce have
