Biology Reference
In-Depth Information
Fig. 6.2
Prioritization of control is required for efforts to be successful through time. For example,
if the river and wind move top to bottom in the diagram, the patches at the top will act as sources
to the bottom. Without control efforts at that source location, any efforts to control the small
infestations would fail
The same concept could be used to prioritize national control and eradication
efforts for particular species. Those species predicted to rapidly spread across a
country, a state, or a county require a more rapid response than those whose spread
may be on the order of decades.
Additionally, different conclusions could be drawn about a species with only a
single point in time observation, highlighting the need for long-term monitoring.
The impacts of an invader may change through time, and this will only be captured
with sampling at multiple points along the invasion time scale. For example, studies
of the red imported fire ant (
Solenopsis invicta
) at two different points of time in
the invasion phase in the same location in central Texas, USA revealed very differ-
ent results (Morrison 2002). Sampling first occurred in the 1980s during the initial
phase of invasion. As the ant species spread, it became dominant and its presence
was correlated with decreases in native ant populations. However, when the same
location was sampled 12 years later, native ant populations had returned to preinva-
sion levels. The fire ant was still the most abundant ant species, but the relative
abundance of the species was drastically different from 12 years before. Examining
either the initial study or the later study singly, very different conclusions would be
drawn. Another example is of zebra mussels (
Dreissena polymorpha
) in the Hudson
River Estuary, USA. Native bivalve populations decreased by 60-100% over the
