Biology Reference
In-Depth Information
establishment of new individuals, whether they be native or alien. Some
habitats present physical conditions that are extreme, others conditions
that are benign. Some provide resources in abundance, others in very lim-
ited quantities. Coevolutionary adjustments of different organisms to each
other seem to be favored by abundant resources and benign habitat con-
ditions.
In addition, stability and predictability of the environment are factors
of great importance to coevolution. Some communities occupy habitats
that are relatively stable, exhibiting nearly constant conditions or showing
seasonal patterns of change that are highly predictable. Spring-fed streams,
tropical lakes, and tropical rain forests experience nearly constant condi-
tions. Temperate rain forests and arctic/alpine tundra show strong, but
highly predictable patterns of seasonal change. Other communities are
subject to irregular events that influence physical conditions and resource
abundance. Examples include most streams and lakes fed by surface runoff
of water from heavy rains, riparian communities bordering streams sub-
ject to flooding, arid-land communities subject to violent weather events,
and terrestrial communities subject to fire. In addition, many communi-
ties and intensively used lands are subject to disturbance by activities such
as farming, grazing, timber harvest, vehicular use, and waste discharge. Sta-
bility and predictability of the environment also favor coevolution.
Stability, Predictability, and Alien Invasions
Disturbance often sets the stage for alien invasions. Environments with
low stability and predictability often present areas of unoccupied habitat
where competition for resources is low.These conditions favor the estab-
lishment of new individuals, aliens as well as natives (Davis et al. 2000).
Many such environments, such as riparian areas subject to flooding, are
also very rich in resources such as water and nutrients. Even though such
habitats may possess a high diversity of native species, many alien species
can also be successful because of the availability of establishment sites and
resources. Some types of disturbance may also create conditions to which
alien species from regions where human disturbance has long been a
powerful evolutionary force are well adapted and native species are not
(Byers 2002).
Since aquatic environments often show instability and unpredictabil-
ity, it is also perhaps not surprising that some aquatic ecologists hold the
view that invasion success is influenced principally by abiotic conditions
of the habitat. Moyle and Light (1996), for example, argued that the
