Abstract
Summary
1. Energy expenditure in wild animals can be limited (i) intrinsically by physiological processes that constrain an animal’s capacity to use energy, (ii) extrinsically by energy availability
in the environment and/or (iii) strategically based on trade-offs between elevated metabolism and survival. Although these factors apply to all individuals within a population, some individuals
expend more or less energy than other individuals.
2. To examine the role of an energy ceiling in a species with a high and individually repeatable metabolic rate, we compared energy expenditure of thick-billed murres (Uria lomvia) with and without handicaps during a period of peak energy demand (chick-rearing, N = 16). We also compared energy expenditure of unencumbered birds (N = 260) across 8 years exhibiting contrasting environmental conditions and correlated energy expenditure with fitness (reproductive success and survival).
3. Murres experienced an energy ceiling mediated through behavioural adjustments. Handicapped birds decreased time spent flying/diving and chick-provisioning rates such that overall
daily energy expenditure remained unchanged across the two treatments. The energy ceiling did not reflect energy availability or trade-offs with fitness, as energy expenditure was similar
across contrasting foraging conditions and was not associated with reduced survival or increased reproductive success.
4. We found partial support for the trade-off hypothesis as older murres, where prospects for future reproduction would be relatively limited, did overcome an energy ceiling to invest more
in offspring following handicapping by reducing their own energy reserves. The ceiling therefore appeared to operate at the level of intake (i.e. digestion) rather than expenditure (i.e. thermal constraint, oxidative stress).
5. A meta-analysis comparing responses of breeding animals to handicapping suggests that our results are typical: animals either reduced investment in themselves or in their offspring to remain below an energy ceiling. Across species, whether a handicapped individual invested in its own energy stores or its offspring’s growth was not explained by life history (future vs. current reproductive potential). Many breeding animals apparently experience an intrinsic energy ceiling, and increased energy costs lead to a decline in self-maintenance and/or offspring provisioning.
1. Energy expenditure in wild animals can be limited (i) intrinsically by physiological processes that constrain an animal’s capacity to use energy, (ii) extrinsically by energy availability
in the environment and/or (iii) strategically based on trade-offs between elevated metabolism and survival. Although these factors apply to all individuals within a population, some individuals
expend more or less energy than other individuals.
2. To examine the role of an energy ceiling in a species with a high and individually repeatable metabolic rate, we compared energy expenditure of thick-billed murres (Uria lomvia) with and without handicaps during a period of peak energy demand (chick-rearing, N = 16). We also compared energy expenditure of unencumbered birds (N = 260) across 8 years exhibiting contrasting environmental conditions and correlated energy expenditure with fitness (reproductive success and survival).
3. Murres experienced an energy ceiling mediated through behavioural adjustments. Handicapped birds decreased time spent flying/diving and chick-provisioning rates such that overall
daily energy expenditure remained unchanged across the two treatments. The energy ceiling did not reflect energy availability or trade-offs with fitness, as energy expenditure was similar
across contrasting foraging conditions and was not associated with reduced survival or increased reproductive success.
4. We found partial support for the trade-off hypothesis as older murres, where prospects for future reproduction would be relatively limited, did overcome an energy ceiling to invest more
in offspring following handicapping by reducing their own energy reserves. The ceiling therefore appeared to operate at the level of intake (i.e. digestion) rather than expenditure (i.e. thermal constraint, oxidative stress).
5. A meta-analysis comparing responses of breeding animals to handicapping suggests that our results are typical: animals either reduced investment in themselves or in their offspring to remain below an energy ceiling. Across species, whether a handicapped individual invested in its own energy stores or its offspring’s growth was not explained by life history (future vs. current reproductive potential). Many breeding animals apparently experience an intrinsic energy ceiling, and increased energy costs lead to a decline in self-maintenance and/or offspring provisioning.
| Original language | English |
|---|---|
| Pages (from-to) | 136-146 |
| Number of pages | 11 |
| Journal | Journal of Animal Ecology |
| Volume | 83 |
| Issue number | 1 |
| Early online date | 18 Dec 2013 |
| DOIs | |
| Publication status | Published - Jan 2014 |
Bibliographical note
AcknowledgementsWe thank our field companions (2006: K. Ashbrook, M. Barrueto, J. Nakoolak, P. Redman, P. Woodward; 2009: J. Nakoolak, J. Provencher, P. Smith and K. Woo; other years: B. Addison, A. Hargreaves, M. Hipfner, G. Langston, S. Jacobs, A. Moody, J. Nakoolak, J. Provencher, A. Ronston, K. Woo), G. Anderson, J. Green, T. Williams and two anonymous reviewers for insightful comments and J. Akearok, C. Eberl and M. Mallory (Environment Canada) and R. Armstrong (Nunavut Research Institute) for assistance with logistics. The study is part of KHE’s PhD thesis, and he benefitted from input by committee members G. Anderson, J. Anderson, K. Campbell and F. Schweizer. P Redman
and P.J. Thomson provided technical support for the isotope analyses. Financial support came from Environment Canada, JFH’s NSERC Discovery Grant, the Polar Continental Shelf Project Natural Resources Canada), the Northern Contaminants Programme (Indian Affairs and Northern Development Canada), the Frank Chapman Fund (American Museum of Natural History), the Taverner and James Baillie Awards (Bird Studies Canada/Society of Canadian Ornithologists), a Sigma Xi grant-in-aid of research, the Animal Behaviour Society and American Ornithologists’ Union Research Grants, the Northern Scientific Training Program and the Fondation Prince Albert II de Monaco. KHE was supported
by an NSERC Vanier Scholarship, a Garfield Weston Northern
Studies Award and the Jennifer Robinson Scholarship (Arctic Institute of North America). MLV was supported by a CNRS and the Fondation des Treilles grant.
Keywords
- device effects
- doubly labelled water
- energy ceiling
- extrinsic limitation
- intrinsic limitation
- repeatability
- thick-billed murre
- Uria lomvia