Behavioral Ecology Of Alaskan Brown Bears (DSI-SRP)
This DSI-SRP fellowship funded Dillon Davey to work in the laboratory of Professor Larisa DeSantis in the Department of Biological Sciences during the summer of 2021. Dillon is a senior majoring in Molecular and Cellular Biology and Medicine, Health, & Society, and minoring in Anthropology.
The project funded by this fellowship aimed to qualify the dietary patterns and varied hunting behaviors of Alaskan brown bears. Previously, Dillon assisted Dr. DeSantis in employing DMTA (dental microwear texture analysis) techniques to evaluate differences in surface wear (Asfc value) on the teeth of Alaksan brown bears from Kodiak Island, Admiralty Island, and the Alaskan Mainland. Interestingly, this data seemed to indicate that bears on Admiralty Island were, on average, eating much softer foods (e.g salmon, elderberries) than bears on either Kodiak Island or on the mainland, evidenced by their significantly less worn teeth, and subsequently lower Asfc values. This, in turn, prompted an investigation into the hunting patterns of individual bears, namely to see how island environments may influence their hunting/foraging behaviors and territorial dominance hierarchies.
This summer, Dillon looked to compare those dental microwear results against measurements from individual bears in order to discover whether body size played a significant role in determining what kinds of food each bear relied on and, in turn, how they hunted for them. Dillon measured images of brown bear mandibles using ImageJ, a Java-based image processing program that can determine the size of an object by measuring its length in pixels. Mandibles were measured in pixels and then compared to a simple reference measurement taken from that same image (e.g 1700px = 10cm) to find the actual dimensions of the jaw. Since the size of a brown bear mandible is known to be a reliable predictor of a bear’s overall body size, these measurements were compared to the DMTA data (Asfc) for each individual bear (based on specimen ID) in a series of linear regressions to see what types of foods they relied on. Dillon hypothesised that in island locales, larger bears would dominate prime fishing regions and demonstrate significantly less dental microwear (lower Asfc) than smaller bears, or even large mainland bears (who are known to instead carve out larger plots of territory to maximize their yield of foraged hard food, such as roots and tubers). Data so far has proved inconclusive, although analysis of island data sets is not yet complete. Despite no conclusive trend having been established for the mainland data set, Dillon’s continued work in the DeSantis DREAM Lab analyzing bears from Admiralty and Kodiak Islands may yield a more definitive pattern among island populations.
In addition to receiving support through a DSI-SRP fellowship, this project was supported and facilitated by the DSI Data Science Team through their regular summer workshops and demo sessions.