Do Ecological Principles Encompass Other Proposed Ecological Theories The River Continuum Concept

Vannote et al. (1980) proposed the RCC (Figure 8.15). For the authors, from headwaters to mouth, the physical variables within a river system present a continuous gradient of physical conditions. This gradient should elicit a series of responses within the constituent populations resulting in a continuum of biotic adjustments and consistent patterns of loading, transport, utilization, and storage of organic matter along the length of a river. Based on the

Figure 8.15 A proposed relationship between stream size and the progressive shift in structural and functional attributes of lotic communities (Vannote et al., 1980).

energy equilibrium theory of fluvial geo-morphologists, they hypothesize that the structural and functional characteristics of stream communities are adapted to conform to the most probable position or mean state of the physical system. They reason that producer and consumer communities characteristic of a given river reach become established in harmony with the dynamic physical conditions of the channel. In natural stream systems, biological communities can be characterized as forming a temporal continuum of synchronized species replacements.

This continuous replacement functions to distribute the utilization of energy inputs over time. Thus, the biological system moves toward a balance between a tendency for efficient use of energy inputs through resource partitioning (food, substrate, etc.) and an opposing tendency for a uniform rate of energy processing throughout the year. The authors theorize that biological communities developed in natural streams assume processing strategies involving minimum energy loss.

Downstream communities are fashioned to capitalize on upstream processing inefficiencies. Both the upstream inefficiency (leakage) and the downstream adjustments seem predictable. Finally, they propose that this RCC provides a framework for integrating predictable and observable biological features of lotic systems.

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