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UBC Theses and Dissertations

Trophic flows across ecosystem boundaries : an examination of the strength and consequences of linkages between stream and forest food webs Marczak, Laurie Beth

Abstract

While empirical examples have demonstrated the openness of ecosystems to resource flows, we still have a limited ability to make general predictions about the magnitude of, or controls on, the effects of subsidies. I studied the impacts of spatial resource subsidies, and the controls on those effects, using several different consumer species in stream and riparian habitats. I quantified the variation in effect size between habitats, recipient consumers, trophic level of the consumer, and productivity of recipient and donor habitats and tested the magnitude of the effect of a subsidy in a system where theory predicted small magnitude or little impact based on productivity contrasts. I tested the consequences of subsidies on the individual fitness of a riparian spider when delivery of a subsidy is variable in time. I demonstrated that the quantity of a subsidy arriving in a recipient habitat may be altered by consumers (waterstriders) feeding at the interface between habitats and that this control varies with habitat type. Overall, three key themes emerge: 1) the identity of consumers and habitats matters, subsidies do not act the same way in all circumstances, 2) the quantity and timing of a subsidy can interact with the specific ecological requirements or life history o f an organism such that a subsidy received at the wrong time in an organism's development may actually have negative consequences for relative adult fitness, and 3) the species composition of both boundaries and recipient habitats may alter the consequences of subsidies. This thesis supports the developing consensus that understanding the factors that determine the response of consumers in a recipient community to a resource subsidy is essential to the development of landscape level approaches to open systems.

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