Consumer adaptation mediates top-down regulation of ecosystems across a nutrient gradient
Type of DegreeDissertation
Fisheries and Allied Aquacultures
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Individuals within a species frequently differ in important traits, and these differences are known functions of genetic, epigenetic, and environmental influences. While evolutionary biologists have been studying genetically-based trait variation within species since Darwin, the ecological consequences of this variation in nature have remained largely unexplored. For my dissertation research, I have investigated the ecosystem-level consequences of local adaptation using a model system consisting of toxic algae (i.e., cyanobacteria) and a keystone herbivore (i.e., the microcrustacean Daphnia pulicaria) that adapts to the presence of toxic cyanobacteria in its environment. I use a combination of large-scale field experiments and mechanistic smaller-scale laboratory experiments to address my questions. While the presence of Daphnia is essential for a strong trophic cascade in lakes, my research shows for the first time that: 1) the effect of different D. pulicaria genotypes on ecosystem function can be as large as the effect of presence/absence of this species; 2) the mechanism is keyed to a superior numerical response of adapted D. pulicaria genotypes not a difference in functional response; 3) the effect of D. pulicara on primary producer biomass increases with productivity, even in the presence of toxic and resistant prey; 4) D. pulicaria and its adaptation to toxic prey can mediate effects on primary producer biomass across a productivity gradient; 5) that tolerance to toxic cyanobacteria by D. pulicaria may be costly in terms of performance in low-nutrient environments; and 6) that D. pulicaria adaptations to toxic cyanobacteria may mediate the response of a toxic and invasive cyanobacterium (Cylindrospermopsis raciborskii) to nutrient enrichment and climate change. In general, human activities have had far-reaching effects on most ecosystems, and these effects are predicted to escalate. The results presented here suggest that the long-term responses of ecosystems to eutrophication (a major agent of global change) may depend not only on the presence of particular consumer species but also on local adaptations by consumers in response to these environmental changes. Given the threat the eutrophication poses to water resources around the world, our findings have important implications for natural resource managers.