| Dualities exist in how we approach and practice ecological science in rivers. These include basic vs. applied ecology and spatial vs. place-based thinking. The study of food webs, or the networks of feeding interactions within ecological communities, is a holistic pursuit that bridges dualities by emphasizing interconnectedness. I constructed flow food webs involving communities of benthic invertebrates and riverine fishes in the free-flowing Methow River of northcentral Washington and the flow-regulated Snake River of southeastern Idaho. Across spatial mosaics of different river-floodplain habitats, I estimated secondary
production, the trophic basis of fish production, organic matter flow, and interaction strengths across environmental gradients and across seasons and years. The overarching objectives of this dissertation were to expand our basic knowledge of spatial characteristics and dynamics of material flow through food webs in complex river-floodplains and examine applied ecological problems associated with each place. In the Methow River floodplain, food webs in the main river channel showed 2-times more complexity than in three side-channel habitats, yet the direction and magnitude of organic matter flow through side-channel food webs expressed more interannual dynamism – a pattern consistent with spatial food-web theory. Secondary production and organic matter flow increased ~3-fold in one side-channel habitat treated with engineered log jams, but this magnitude of change fell within the range of natural variation observed in nontreated habitats. In a springbrook-side-channel mosaic of the Snake River, which has lost large-scale floods for 20 years due to flow-regulation, the magnitude of material flow and interaction strengths between invertebrates and fishes was ~7X greater in scoured habitats where fishes consumed ~50% of total benthic invertebrate production. Furthermore, >50% of the food-web interactions contributed by introduced species to the floodplain-scale meta-food web occurred in multiple habitats, whereas 70% of the interactions involving indigenous species occurred in only a single habitat, suggesting introduced species drove spatial homogenization. These findings illustrate that river food webs were highly dynamic through time and altered by human-induced flow modification and species introductions. Together, these studies combined basic and applied investigations, spatial and place-based thinking, and promoted a more holistic vision of riversfloodplains and their ecological communities. |