Content area
Full Text
A multitrophic model integrating the effects of flooding disturbance and food web interactions in rivers predicted that removing floods would cause increases of predatorresistant grazing insects, which would divert energy away from the food chain leading to predatory fish. Experimental manipulations of predator-resistant grazers and top predators, and large-scale comparisons of regulated and unregulated rivers, verified the model predictions. Thus, multitrophic models can successfully synthesize a variety of ecological processes, and conservation programs may benefit by taking a food web perspective instead of concentrating on a single species.
Although conservation programs typically concentrate on the direct impacts of environmental change on a single species, ecological experiments and theory demonstrate that species are affected in complex ways by other species, ecosystem productivity, and disturbance regimes (1-4). Therefore, to understand and predict the consequences of impacts on the environment, ecologists must shift from an autecological perspective to consideration of the interaction of multiple causal factors. For example, changes in climate, land use, and water regulation or diversion all may alter the flooding regime of rivers. How do changes in flooding disturbance affect species in river food webs? Successfully predicting the answer to this question requires a framework that can synthesize the direct effect of disturbance-induced mortality, as well as the indirect compensatory or reinforcing effects of interactions among various species in an ecological community.
Multitrophic dynamic models of species interactions provide a potentially useful synthetic theoretical framework to simultaneously examine a variety of ecological processes (1, 2). Within this framework, species interactions are modeled explicitly, and the dynamics of limiting resources can be treated as species at the bottom of the food web. Disturbance can be incorporated by adding density-independent mortality terms to the dynamics of each species. In previous studies of rivers in northern California, we have shown that such a framework can predict the consequences of removing top predators from a food web and of varying productivity at the base of the food web ( 1, 3). Here, we consider whether the effects of disturbance can also be incorporated into such a theoretical framework.
Our observations of free-flowing rivers in northern California during the droughts of 1990-1992 and 1994, when scouring floods typical of the winter rainy season were absent or reduced, indicated that...