From elements to landscapes: the role of terrestrial consumers in ecosystem functioning

Rizutto, Matteo (2021) From elements to landscapes: the role of terrestrial consumers in ecosystem functioning. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Consumers are key actors in ecosystems, shaping processes and functions at multiple spatiotemporal scales via their interactions with biotic and abiotic ecosystem features. Yet, research on the dynamics of local and meta-ecosystems rarely accounts for the effects of consumers— particularly terrestrial mammals. Two hurdles hamper progress in this field: the lack of common units of measurement for biotic and abiotic ecosystem components, and the need for flexible, system-agnostic ways to investigate how consumers interact with and influence ecosystem functioning. In this dissertation, I offer a concerted approach to address these issues, integrating wildlife, landscape, and ecosystem ecology within an ecological stoichiometry framework. I begin by showing that terrestrial mammals are variable in their ecological stoichiometry, using data from the snowshoe hare (Lepus americanus), a keystone boreal herbivore. Importantly, unlike invertebrates, organismal stoichiometry in vertebrates appears unrelated to age, sex, body size, and body condition. Building on these results, I investigate the responses of terrestrial herbivores to biotic variability in their environment, finding that snowshoe hares vary their space use when facing intraspecific variability in the stoichiometry of their foraging resources. Hares had larger home ranges in areas of poor or highly variable forage stoichiometry compared to areas of high and consistent forage stoichiometry. This differential space use by consumers may elicit changes in both their ecology and ecosystem dynamics. Thus, I develop a novel mathematical model of a meta-ecosystem to investigate how multiple types of consumer movement over the landscape influence ecosystem processes and functions. Expanding a classic, two-patch meta-ecosystem model to include the surrounding matrix, I demonstrate that active, non-diffusive movement of consumers can reduce or enhance ecosystem functions at local and regional spatial scales. Throughout my thesis, ecological stoichiometry ties together the diverse themes of each chapter, further demonstrating how elemental currencies can work as shared units of measurement across levels of biological organization. Overall, my thesis combines a laboratory study, spatial statistical models fit to a field-based case study, and a novel mathematical model to provide testable predictions to guide future research into the role of consumers within meta-ecology.

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