Environmental Engineering Reference
In-Depth Information
Some of the key patterns captured by this model mirror patterns observed in
field data on Everglades aquatic communities. For example, when marshes are re-
flooded following the dry season, the density of fish and some invertebrates is low
in both the newly re-flooded and continually inundated marshes. The principles of
this mechanism are depicted in Fig.
18.6
. It has recently been noted that the strength
of top-down biotic interactions declines following a re-flooding event and that the
interaction web varies seasonally and spatially, depending on the position in the
landscape and history of drying at the site and around it (Trexler et al. 2005; Liston
2006). Another major issue for wetland management is the issue of permanently
flooded water bodies, like canals and swales. These were built to serve engineering
purposes; that is, to expedite water movement and storage. However, there is
growing evidence that permanently flooded areas may provide opportunities for
introduced piscivorous fishes to persist in systems historically lacking such pre-
dators or become stabilized to their presence at low density (Cucherousset et al.
2007; Rehage and Trexler 2006). Future work with this model format can improve
our hypotheses about the role of permanent aquatic refuges in marsh ecosystems,
particularly in a landscape framework, to better direct future research on this
important management topic.
The fascinating mechanisms of trophic cascading effects are not only an enrich-
ment to ecological theory, but can also be applied to management and conservation
issues of aquatic and semi-aquatic ecosystems, where they help to understand the
complex dynamics and variability in the participating hierarchical levels.
Fig. 18.6 (continued) between these functional groups can occur in the marshes. (b) As water
levels recede, large fish and then small fish move into refugia of deeper water. (c-d) If water levels
reach low levels, deep ponds and solution holes may be the only refugia remaining. Intense
predation by large fish on small fish may take place in the ponds. When the water levels rise
again, the remaining fish can explore the hydroscape and the cycle continues [modified from
DeAngelis et al. (1997), illustration by M. Trexler]
