Murray M. Humphries
NSERC Postdoctoral Fellow

Department of Zoology
University of Aberdeen
Aberdeen, UK
AB24 3TZ
(44) 1224-273637

Department of Biological Sciences
University of Alberta
Edmonton, Alberta, Canada
T6G 2E9
(780) 492-1297

Email: murray_humphries@hotmail.com

Research Interests
In general, I am interested in how physiology and behaviour influence higher level ecological processes like reproductive success and population dynamics. My research to date has focused mainly on small mammal energetics, examining various physiological, behavioural, and ecological questions related to how animals acquire and expend energy. Some current projects I am working on include:

The Ecology of Metabolism in Red Squirrels (NSERC PDF project)
In collaboration with Prof. John Speakman, University of Aberdeen, and Prof. Stan Boutin, University of Alberta, I am currently studying links between food availability, physiology, behaviour, and reproductive success in a free-ranging population of red squirrels (Tamiasciurus hudsonicus) near Kluane Lake, Yukon.

North American red squirrel (Tamiasciurus hudsonicus)  Photo by T. Karels.

This population has been the subject of a long-term study of parental care and reproductive success in a seasonally and annually variable environment, and thus is ideal for evaluating physiological responses to food and climate with an ecological context. My research involves manipulating individual food availability in autumn, measuring physiological and behavioural responses in mid-winter and spring, and documenting subsequent reproductive success and survival. The physiological responses we will attempt to measure range from resting, field, and summit metabolic rates to circulating leptin and hypothalamic neuropeptide expression. If successful, this research will provide one of the best field studies to date of the physiological mechanisms underlying population responses (or non-responses) to resource availability.

Temperature, Energetics, and the Biogeography of Hibernating Bats
In collaboration with Prof. John Speakman, University of Aberdeen, and Prof. Don Thomas, University of Sherbrooke, I investigated whether a bioenergetic model can be used to predict the microhabitat selection and biogeography of hibernating little brown bats (Myotis lucifugus). The model, which is based on simple thermal relationships that define the length and energetic costs of hibernation in different localities, is remarkably successful in predicting the observed microhabitat and biogeographical distributions of this species.

Given current climate change scenarios, the model predicts a dramatic northward expansion of M. lucifugus within the next twenty years shown in the above figure. The current northern limit to the distribution is shown in blue and the anticipated northern limit to the range in 2020 is shown in red.. The model thus demonstrates how basic bioenergetic information can be used to link climate and biogeography, which in turn permits anticipation of the consequences of climate change.

Metabolic Variability and the Stability and Coexistence of Mammalian Populations
In collaboration with Prof. Kevin McCann, McGill University, I am investigating some general ecological implications of the energetic flexibility created by adaptations like food hoarding and torpor. In a temporally variable environment, the capacity of some endotherms to store energy when times are good and reduce expenditure when times are bad should serve as a buffer against resource fluctuations. We use consumer-resource population models and multi-species comparisons to examine the implications of these adaptations at the population level.

The results show that differential energetic flexibility can explain why some endotherm populations persist through periods of food shortage better than others and potentially why different populations can coexist on shared resources. Intriguingly, this suggests that metabolic variability may be a basic axis of differentiation underlying key ecological processes like stability, coexistence, and the maintenance of biodiversity.

Food Hoarding and Hibernation in Eastern Chipmunks (PhD Project)
In collaboration with Prof. Donald Kramer (McGill University) and Prof. Don Thomas (Sherbrooke University), I have been studying the interaction between food hoarding and torpor expression in chipmunks. Eastern chipmunks (Tamias striatus) accumulate a large hoard of tree seeds in their burrow during autumn then reduce their over-winter consumption of this hoard via torpor expression. Chipmunks thus spend winter hibernation in an underground burrow alternating between long bouts (days to weeks) of torpor, when body temperatures and meatabolism are less than 10% of normal, and short bouts (hours to days) of normal body temperature and metabolism, when physiological recovery and food ingestion occur.

Chipmunk (Tamias striatus) Photo by C. Hall.

I studied digestive physiology in captive chipmunks to determine if food can continue to be digested during torpor, permitting individuals to re-enter torpor immediately after food has been ingested. My results suggest that digestion does in fact proceed very well during torpor, permitting chipmunks to spend much more time in torpor than otherwise would be possible. The surprising capacity of chipmunks to digest food at low body temperatures suggests that their digestive enzymes function more like those of ectothermic reptiles and amphibians than many other birds and mammals. I also evaluated what determines the timing of the transition between autumn hoarding and winter hibernation in chipmunks. The results suggest the transition may depend on a complex and potentially variable interaction between increasing thermoregulatory requirements, reduced food availability, and accumulated food hoard reserves. Finally, I studied whether chipmunks modified their use of torpor during winter according to the amount of food that was present in their burrow hoard. The results were striking - chipmunks with supplemented hoards spent more than 80% of the time at normal body temperatures while control animals spent less than 40% of the time at normal body temperatures. This demonstrates that chipmunks can and do modify their torpor expression according to some external cue about the size of their food hoard, and hints at the presence of important costs of torpor in mammalian hibernators.

Publications

Humphries, M.M., D.W. Thomas, and D.L. Kramer. 2001. Torpor and digestion in food-storing hibernators. Physiological and Biochemical Zoology 74, 283-292.

MacArthur, R.A., M.M. Humphries, K.L. Campbell, and G.A. Fines. 2001. Body oxygen stores, aerobic dive limits, and the diving abilities of juvenile and adult muskrats. Physiological and Biochemical Zoology 74,178-190.

Humphries, M.M. and S. Boutin. 2000. The determinants of optimal offspring number in free-ranging red squirrels. Ecology 81, 2867-2877.

MacArthur, R.A. and M.M. Humphries. 1999. Postnatal development of thermoregulation in the semiaquatic muskrat (Ondatra zibethicus). Canadian Journal of Zoology 77, 1521-1529

Humphries, M.M. and S. Boutin. 1999. Mass-dependent reproduction or reproduction-dependent mass? A comment on body mass and first-time reproduction in female sciurids. Canadian Journal of Zoology 77, 171-173.

MacArthur, R.A., M.M. Humphries, and D. Jeske. 1997. Huddling behavior and the foraging efficiency of muskrats. Journal of Mammalogy 78, 850-858.

Humphries, M.M. and S. Boutin. 1996. Reproductive demands and mass gains: a paradox in female red squirrels (Tamiasciurus hudsonicus). Journal of Animal Ecology 65, 332-338.

Education

Ph.D. May, 2001. Department of Biology, McGill University, Montreal, Quebec.

M.Sc. February, 1996. Department of Biological Sciences, University of Alberta. Edmonton, Alberta.

B.Sc. (Hons.) April, 1993. Department of Zoology, University of Manitoba. Winnipeg, Manitoba.

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