I studied 19 public and private bison herds from Saskatchewan to Texas throughout the Great Plains to test mechanistic approaches explaining body size change in bison, which have approximately a 30% disparity between northern and southern herds. The two pathways that are likely the culprits are heat loads (thermoregulation) and nutrition.
If we can understand how bison adapted to climate changes in the past and today, then we can implement appropriate management practices that will facilitate supply and demand quotas from the consumers while conserving a sustainable populations on our nation's public and private rangelands.
If we can understand how bison adapted to climate changes in the past and today, then we can implement appropriate management practices that will facilitate supply and demand quotas from the consumers while conserving a sustainable populations on our nation's public and private rangelands.
Background: |
It has been long understood that populations of species that live closer towards the polar regions are larger than those populations that are closer towards the equatorial regions, commonly referred to as Bergmann's Rule, which was established in 1847. More simply, populations of animals have larger body sizes in colder climates than those of warmer climates. However, the underlying mechanisms that drive body size have not been well understood for the last 150+ years. It has been proposed that there are many mechanisms that may drive body size in relation to warming climates. I am comparing and contrasting two major mechanisms, thermoregulation and nutrition, as possible drivers that explain body size. I have been working towards understanding these mechanisms using a three-pronged approach, 1) describe phenomenon using the long-term fossil record of climate change and bison body size change, 2) measuring the affect of direct seasonal heat loads using a thermal imaging camera, and 3) using carbon and nitrogen stable isotopes to describe seasonal energy and protein assimilation and recycling. This is the first time that both mechanisms have been directly measured in a single meta-population (collectively the 19 herds) across similar space and time scales.
My research has found that if we look at fossil bison from 40,000 years ago (during the last Ice Age) to today, we can model the rate of change of body mass as it directly relates to global temperature. The last Ice Age was approximately 6 degrees Celsius cooler than today and it is expected to continue to rise in global temperature by 2-4 degrees in just 3-8 decades. Bison were twice as large during the Ice Age compared to bison today and are expected to decrease by almost half again as global temperatures increase. Bison decrease in body size by approximately 41 to 60 kg per degree Celsius.
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The thermal imaging camera simultaneously captures the infrared spectrum and the visible spectrum. Using photogrammetry methods, I can measure the real-world dimensions of height, length, and surface area of the animal. This is essential for calculating a snapshot of the Watts of energy that the bison exchange with their ambient conditions, whether it be seasonal or extreme weather events.
This research was supported, in part, by the US National Science Foundation Adaptation to Abrupt Climate Change IGERT program grant DGE-1144423.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Other funding of this research was provided by the Boone & Crockett Club in the Department of Wildlife and Fisheries Sciences at Texas A&M University, the Western Bison Association, the Explorers Club, and the National Buffalo Foundation.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Other funding of this research was provided by the Boone & Crockett Club in the Department of Wildlife and Fisheries Sciences at Texas A&M University, the Western Bison Association, the Explorers Club, and the National Buffalo Foundation.