Submitted to: American Fisheries Society Book Series
Publication Type: Book / Chapter
Publication Acceptance Date: 12/21/2009
Publication Date: 8/19/2010
Citation: Gido, K.B., Bertrand, K.N., Murdock, J.N., Dodds, W.K., Whiles, M.R. 2010. Disturbance mediated effects of fishes on stream ecosystem processes: concepts and results from highly variable prairie streams. In: Gido, K., Jackson, D. (Eds.). American Fisheries Society Book Series, Bethesda, MD. pp.593-617. Interpretive Summary: Stream fishes can have strong effects on ecosystem processes through the consumption of algae and invertebrates, and excretion of nutrients that feed algal growth. However, varying flooding and drying patterns and different fish communities across streams makes it difficult to generalize fish impact. To evaluate the role of fishes following flood and drying, we used a series of experiments that measured the influence of fish groups with different feeding styles (bottom-feeders and water column-feeders) following floods and drying in prairie streams, and a conceptual model was developed. We found that fish impacts were variable among feeding styles, but are generally predicted to be greatest shortly after a disturbance when algal and invertebrate communities are less complex and their biomass is low relative to fish biomass. Our analysis underscores the importance of hydrology and species composition when predicting the consequences of biodiversity loss in streams with variable or human-modified disturbance patterns.
Technical Abstract: Stream fishes can have strong top-down and bottom-up effects on ecosystem processes. However, the dynamic nature of streams constrains our ability to generalize these effects across systems with different disturbance regimes and species composition. To evaluate the role of fishes following disturbance, we used a series of field and mesocosm experiments that quantified the influence of grazers and water-column minnows on primary productivity, periphyton structure, organic matter pools, and invertebrate communities following either scouring floods or drying of prairie streams. Results from individual experiments revealed highly significant effects of fishes, but the direction or magnitude of effects varied among experiments. Meta-analyses across experiments indicated that grazers consistently reduced the relative amount of fine benthic organic matter (FBOM) and chironomid abundance within 2 weeks after disturbances. However, effect sizes (log response ratios) were heterogeneous across experiments for algal biomass and algal filament lengths measured > 4 weeks after a disturbance, and potentially associated with system productivity and grazer densities. A similar analysis of 3 to 4 experiments using water-column minnows only found a consistent trend of decreasing FBOM in fish treatments relative to controls when measured < 2 weeks after disturbances and increase in gross primary productivity measured > 4 weeks after disturbance. These results, along with those of others, were used to develop a conceptual framework for predicting the potential role of fishes in streams following disturbances (flood and drying). Both theoretical and empirical research shows that recovery of stream ecosystem processes will depend on the resilience of autotrophic and heterotrophic communities following disturbance. Fish effects may vary among functional groups, but are generally predicted to be greatest during early stages of succession when algal and invertebrate communities are less complex and their biomass is low relative to fish biomass. Our analysis underscores the context dependency of consumer effects on ecosystem structure and function in non-equilibrium conditions and suggests that factors regulating fish densities and colonization of algal and invertebrate taxa need to be evaluated to predict the consequences of biodiversity loss in streams with variable or human-modified disturbance regimes.