Bioenergetic Considerations in the Analysis of Stream Ecosystems

Abstract

The major objectives of this paper are to summarize and synthesize what we know about the energetics of lotic systems, to identify some of the major gaps in our knowledge, and in so doing to provide guidance for new research directions. We identify the major abiotic forcing functions and their connections with terrestrial and stream biota. We further identify how forcings and feedbacks loops are likely to affect the biomass and production of biotic components. A review of the literature suggests that there are several major gaps in our understanding of stream bioenergetics. Most importantly, few comprehensive studies of stream bioenergetics integrate all levels of production, and organic matter budgets rarely have been combined with production analyses beyond the primary producers. In addition, secondary production studies in the tropics are largely lacking. Most bioenergetics studies to date have been descriptive, and there is a major need to study those abiotic and biotic factors which control bioenergetics in streams across biomes and latitudes. The importance of floodplains and the role of dissolved organic matter have not been adequately incorporated into our understanding of stream bioenergetics. We need to determine if some generally applicable organismal-environmental relationships can be used to predict energetic characteristics across streams. Major new initiatives are required to answer some of the larger scale questions. Several approaches are possible: (1) synoptic analysis of multiple streams to compare within-region variance with between-region variance, (2) experimental manipulation of entire streams or their catchments to test factors that control bioenergetics, (3) the use of batteries of experimental streams to help isolate cause-effect relationships, and (4) the further development of computer models that incorporate abiotic forcings and bioenergetics.