Environmental Engineering Reference
In-Depth Information
Chapter 18
Trophic Cascades and Food Web Stability
in Fish Communities of the Everglades
Fred Jopp, Donald L. DeAngelis, and Joel C. Trexler
Abstract We introduce the trophic organisation structure of aquatic ecosystems by
giving a short overview on some classic landmarks from ecological theory. The
concept of trophic cascades describes interactions in food webs that descend the
whole structure. They start at the top node of the highest carnivores, the piscivores,
by increasing the piscivore's biomass which in turn triggers changes in the succes-
sive trophic hierarchical levels. The concept of trophic cascades has long since
passed from theoretical into applied ecology. We demonstrate this with an example
of a spatially-explicit simulation model that is used to understand the high varia-
bility in the aquatic trophic structure of the Everglades marshland. Changes in
hydrology of the Everglades over the last several decades have reduced the hydro-
period in some areas and may have diminished foraging fishes and their food base.
A key component for restoring fish productivity to historic levels is to understand
and to improve the spatio-temporal water patterns in the wetlands. Therefore, by
applying the simulation model we investigated the dynamics of an aquatic food
web with the following components: primary producers, detritus, invertebrates,
fish consumers and nutrients. For this purpose, a hydroscape of 20
20 km was
modeled that shows a natural-like elevation gradient. The annual fluctuations
in water level were imposed as sinusoidally changing hydrology on the whole
system, which resulted in dynamic patterns of flooded and non-flooded areas. We
performed long-term simulations over a period of 10 years and examined how the
trophic levels reacted to changes in the water level; in particular, how the changing
water levels affected trophic cascades. We discuss the consequences of these
results for management and restoration of the Everglades aquatic communities.
