Dr. Jack Millar
Evolution of mammalian life-history strategies
Visit Dr. Millar's web site
Millar to Study Annual Small Mammal Population Dynamics thanks to Distinguished Research Professorship
by Mitchell Zimmer
Prof. Jack Millar of the Department of Biology is one of the recipients of the Distinguished Research Professorships for 2007-2008. These awards release qualified science faculty from their teaching duties to provide an essential opportunity to concentrate, focus and reflect on their research.
Millar studies the population dynamics of small mammals such as wood rats, voles and especially deer mice in sub alpine or northern regions. Given that these environments have very short reproductive seasons he wondered how these animals survived with such limited breeding opportunities. The answer turned out to be a matter of longevity. “A mouse born in the spring here is dead by September. The mice that we work on in the north, they can’t even mature until they are a year old, so we have two and three year old mice running around,” says Millar. As with any research the answer to one question soon led to more questions. Millar asked, “Why can’t they breed earlier? Why can’t they breed in winter?” During the last twenty years of looking into the problem and fixing the parameters in various species, Millar found that, “one of the strongest constraints that the populations have or appear to have is in the food base.”
Millar found that if he supplemented the diet of deer mice with a high protein quality food (which happened to be cat food) they were able to coax the earliest born mice to breed that same summer, further, these mice were able to breed earlier in the spring. Even though Millar’s team had artificially adjusted the breeding habits of these mice, the questions remained; what were these mice feeding on in the natural world and does that affect the breeding cycle? The problem here was that these mice are small, nocturnal and chew their food very fine. “You can’t study their foraging directly,” says Millar, “we know they’re omnivorous, they feed on seeds and insects.”
This is where Western’s Laboratory for Stable Isotope Science (LSIS) turns out to be very helpful. The elements of nitrogen and carbon are very important in the formation of biological components such as protein and DNA. Over 99% of the nitrogen in the environment is of the isotope 14N (that means there are 7 protons and 7 neutrons within the atomic nucleus) the remaining proportion is made up of 15N (7 protons and 8 neutrons within the nucleus making this isotope almost act the same chemically but weighs a bit more). As animals and insects eat, the heavy isotope is enriched as it accumulates in tissues while the 14N is preferentially excreted. Much the same can be said for the isotopes of carbon 12C and 13C. If deer mice are feeding on insects rather than seeds, then the increased concentration of the heavier isotopes detected by the LSIS could determine that these mice are working on a different level within the hierarchy of the food chain.
Millar’s lab has been busy acquiring some baseline data such as maintaining a fixed diet and tracking the isotope composition of the food as it underwent digestion, examining the turnover rates in different tissues; they even studied mother-offspring relationships. “The next step is to get out of the laboratory and examine how isotopes change under natural conditions.” Millar adds, “The other thing that we need to know is to see how the stable isotopes change within the system on an annual basis.” This next step will require Millar to take samples throughout the whole year and the Distinguished Professorship will allow him to do just that. Millar will be busy travelling between Western and the Kananaskis valley in Southwestern Alberta to a field station run by the University of Calgary. Here the animals are trapped live and released after hair samples are taken for isotope analysis. The goal is to set up a protocol so that Millar can analyse samples from various populations in different habitats to determine what kind of a balance they have in their diet.
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This page was last updated on
November 5, 2010
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