Trophic Cascades and Food Web Stability in Fish Communities of the Everglades

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 successive 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 variability in the aquatic trophic structure of the Everglades marshland. Changes in hydrology of the Everglades over the last several decades have reduced the hydroperiod 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.