Biology Reference
In-Depth Information
5-year period following the initial invasion of zebra mussels in 1991 (Strayer and
Malcom 2007). However, monitoring of the four most common native bivalves
since 2000 showed stabilization or recovery of their populations, despite the endur-
ing presence of zebra mussels. Continued monitoring through the stages of invasion
like the examples above is necessary to determine what long-term impact invaders
may have on native populations as single point in time observations are not accurate
to determine the long-term trajectory of ecological communities. These conclusions
about long-term impacts are useful in prioritizing control efforts to focus on species
that may have greater long-term effects. A species that impacts native populations
throughout the entire invasion process may have a higher priority for early detec-
tion and removal in new areas than ones whose impacts decrease over time.
6.4.2 Long-Term Viewpoint
Once control efforts have been carried out, it is necessary to monitor the location
and effects. If control of a particular species occurs, and the organisms that occupy
the space after control are different invasive species rather than native vegetation,
the question must be asked whether the control efforts were effective. Understanding
what state control efforts are trying to restore a location to is important. This tem-
poral view can aid in setting priorities for resources to areas where control efforts
will have the desired effect through time rather than only over the short term, like
a single growing season.
Another temporal aspect of control prioritization relates to the spatial configura-
tion of infestations. The frequency and number of individuals introduced is highly
correlated with establishment success (Colautti et al. 2006; D'Antonio et al. 2001;
Kolar and Lodge 2001). It only follows, then, that this factor should be included in
determining locations for control efforts. For example, if there is an adjacent popu-
lation that could easily provide propagule supplies that is not controlled, then a
temporal view of control efforts suggests that a different approach should be taken:
controlling source populations before focusing on other populations, or controlling
both at the same time to eradicate the smaller infestation while decreasing the prop-
agule supply from the well-established population.
One common management practice is for government agencies to re-seed areas
after fires. Managers reseeded three areas in the Grand Staircase Escalante National
Monument in Utah burned in July 1996, July 1997, and August 1998 (which partly
overlapped the 1996 burn) with native and nonnative seeds, two different native
only seed mixes, and no seeding, respectively. Sampling both burned and adjacent
unburned sites in 2000 revealed differences in response to reseeding at different
locations (Evangelista et al. 2004). In one case, the treatment of native only seeding
in a burned area resulted in greater similarity to undisturbed sites in relation to
native and nonnative plant species richness and cover. A different location with this
same treatment (native only seed and burned), however, was more similar to the
untreated burned area and generally remained high in nonnative species richness.
