Population and community consequences of cross-ecosystem resource subsidies

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Many ecosystems depend on cross-ecosystem resource subsidies, such as leaf litter or terrestrial invertebrates falling into streams, as key energy resources to sustain their productivity and biodiversity. This dependence is particularly clear for ecosystems that are detritus-based, but include many other resource types and ecosystem types. Resource subsidies cross many ecosystem boundaries, but are most obvious across the land-water interface. These resources are considered to be subsidies to the in situ production of basal resources, and are characterised in part by being donor-controlled since consumers cannot affect the rates of input of the subsidy resource, and therefore there is no, or negligible, direct feedback. It has been demonstrated that these resources are essential, and work on the topic within the past 5 years have allowed theory to advance to the stage of predictive, quantitative models. We have made progress on flows of these subsidy resources into and out of streams by quantifying the relative effects on consumer populations and their communities. We are now able to ask more specific questions about the quantitative form of the relationships between these subsidy resources and the consumers' dynamics. Moreover, we can ask how resource subsidies affect community processes, including questions about stability, community assembly, productivity, and invasibility. In this proposal I intend to address questions to advance the field of consumer-resource dynamics for subsidy-based systems using experimental approaches in stream and riparian ecosystems. These questions revolve around the effects of the timing, magnitude, duration and quality of resource subsidies. The questions address population and community level consequences, possibility of enhancing or diminishing trophic cascades, the stability of foodwebs, studying the response surfaces of consumer dynamics in response to subsidies, and effects of quality and timing of resource flows. These experiments will take advantage of past investments by NSERC, CFI and UBC in our infrastructure at UBC's Malcolm Knapp Research Forest.