Garcia Gomez, Guillermo
(2023)
The role of growth in metabolic scaling: a case study across habitats and life histories.
PhD thesis, University of Liverpool.
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Abstract
All life processes are powered by metabolism, and thus the metabolic rate of organisms provide a measure of their pace of life. Metabolic rate is linked to body size by many biological processes, involving self-maintenance, biomass production, and activity, all three ultimately related to fitness. Explaining the degree of variation in metabolic rate with body size has therefore become a central topic for ecologists, yet the mechanism(s) underlying this relationship, often termed metabolic scaling, remain enigmatic. In this thesis, I investigate the variation in metabolic scaling in response to different ecological and organismal factors in a broad diversity of ectotherms from extremely different habitats. First, using a meta-analytic approach, I determine the change in metabolic scaling within species of ectothermic vertebrates under both increasing temperature and activity level, exploring differences between air- (i.e., reptiles and amphibians) and water-breathing organisms (i.e., teleost fish and elasmobranchs). I demonstrate that scaling slopes become shallower as metabolic level (i.e., the elevation of the metabolic rate vs. body mass relationship) increases with warming only in water-breathers, whereas slopes steepen as metabolic level increases with locomotory activity only in air-breathers. I explain these contrasting findings by combining various, complementary hypotheses involving mechanisms that evolved to protect aerobic scope in fish. Second, I show that allometric (log-log) metabolic scaling slopes decrease with increased maximum growth rates across species of teleost fish, suggesting that growth demands influence metabolic scaling. Using a theoretical model, I then characterise the energetic demands at rest in these teleost species, and show that growth costs remain largely invariant with species body size, lifestyle, and evolutionary history. These results highlight that systematic differences in metabolic scaling are important to understand different energy allocation strategies of species. Last, I examine ontogenetic shifts and sexual differences in metabolic scaling in a model crustacean species (Artemia franciscana), showing that variation in scaling slopes can be affected by changes in costs of biomass production between ontogenetic phases and reproductive modes. The potential roles of the cellular mode of growth on production costs and hence on metabolic scaling in this species are discussed. Overall, this thesis combines multiple mechanisms including evolutionary adaptations, plastic responses, and metabolic costs of various organismal activities, to explain the variation in the mass-scaling of energy use among ectotherms and at various levels of biological organisation. Such a multi-mechanistic perspective may be crucial not only for a comprehensive understanding of metabolic scaling, but also to predict the impact of global change on animal communities.
| Item Type: | Thesis (PhD) |
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| Divisions: | Faculty of Science and Engineering > School of Environmental Sciences |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 22 Aug 2023 14:53 |
| Last Modified: | 22 Aug 2023 14:54 |
| DOI: | 10.17638/03170801 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3170801 |
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