Population and food web responses to variation in rates and timing of pulsed, cross-ecosystem resource subsidies

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Many ecological communities receive resource inputs from adjacent ecosystems, sometimes very pulsed in time, such as leaf litter or terrestrial invertebrates falling into streams and wetlands in forests. Studies have shown that these “cross-ecosystem resource subsidies”, such as leaf litter, invertebrates, salmon, sea wrack, pollen and others, contribute in a large way to the productivity of the receiving ecosystems. However, most experiments on this topic involve binary comparisons based on augmentation or exclusion of a subsidy resource compared with an ambient reference or control. We have a limited understanding of how the quantitative effects of variation along characteristics of input rates, timing, duration and resource quality affects recipient population dynamics and productivity, community processes, and stability. ******In our research we have used leaf litter or terrestrial invertebrate inputs to streams as models to test the effects on receiving consumers. However, questions about consequences of quantitative gradients in input characteristics still need study in terms of population and community dynamics. Some stream predators use subsidy resources directly, and we have used cutthroat trout as a model system for understanding how inputs of terrestrial invertebrates affects their growth and reproduction. However, there are few studies of the consequences for population dynamics of those predators, including invertebrates, which do not directly use subsidies themselves, i.e. effects moderated through food webs. Food-web size structure is likely important given that predators (invertebrates and vertebrates) span several orders of magnitude in mass in food webs, and yet predators are often grouped as a single functional category. Thus, we will also test questions of size-dependent responses of consumers. Further, increases in productivity of recipient consumers have rarely been followed carefully into other parts of their food webs, which we will address.******We have used field-based experimental manipulations to test the effects of input rates and quality of subsidies, and have made some progress on considering how these characteristics affect recipient populations and communities. The work proposed here will expand our understanding and predictive capability of how pulsed resource subsidies affect the productivity and stability of recipient populations and communities. Moreover, this work will serve to demonstrate the importance of protecting and managing ecosystems adjacent to aquatic environments, e.g. in forestry, agricultural and urban settings, to sustain productive and healthy freshwaters.*****