Date of Award
H. Thomas Goodwin
From early May through late September, 2012, we captured, tagged, and collected body masses from multiple, free-ranging thirteen-lined ground squirrels (Ictidomys tridecemlineatus) in southwestern Michigan, with 14 individuals recaptured 1 or more times through the season. Beginning in mid-June, we captured and euthanized 12 or these individuals (on average, about 1 per week) to allow study of their lower incisors. We serially micro-sampled enamel along squirrel incisors using laser ablation and determined stable isotope ratios (d13 and d18 O) with gas chromatography-isotope-ratio mass spectrometry (GC-IRMS). The resulting values fell into two spatial groups. Specimens collected within 25 m of a cornfield displayed more positive d13 C values consisted with a C4 plant-rich diet (corn is a C4 plant) and appeared to show a seasonal peak in C4 use (higher d13 C values) late in the season. In contrast, specimens collected in isolated fields separated by buildings and pavement from the cornfiled exhibited more negative values of d13 C consistent with a C3-plants diet. d18 O values did not show distinct spatial grouping and were difficult to interpret. Although a cornfield is an artificial ecosystem, the difference in fractionation between C3 and C4 diet displayed in the stable carbon isotope profiles demonstrate the sensitivity of isotopic analyses of small teeth for elucidating small-scale geographic variation in food availability. Further use of this technique may provide additional evidence for fine-scale spatial and seasonal variation of modern diet and provide a model for further investigation of paleoseasonality using fossil rodent incisors.
Brassington, Jacob Andrew, "Spatial and Seasonal Signals in Stable Isotopes of Incisor Enamel from Free-ranging, Thirteen-lined Ground Squirrels" (2013). Honors Theses. 58.
Thirteen-lined group squirrel, Ground squirrels, Incisors, Stable isotopes., Teeth.
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