2018-2019 Faculty Research Grants
H. Thomas Goodwin (Biology)
Variation in Diet by Season, Age, and Gender in Thirteen-lined Ground Squirrels (Ictidomys Tridecemlineatus)
Prior work in my lab demonstrated an abrupt, transient increase in 𝛅13C (a measure of 13C/12C ratio) during late August and September in the growth record of incisors from thirteen-lined ground squirrels immediately preceding entry into hibernation. Based on published studies, this spike in 𝛅13C indicates an abrupt increase in the proportion of C4 plant-based foods during late summer. However, preliminary studies of diet across the active season failed to uncover the causes of this shift. Alternative hypotheses for the late-season spike in C4-based foods include: a) use of late-season C4 plants that were locally abundant at that time, and b) use of insects that fed on C4 plants and are abundant in late season. The latter hypothesis is consistent with the proclivity of thirteen-lined ground squirrels to consume insects, with insects (especially grasshoppers) heavily utilized in late summer and early fall in one study (Flake 1973). Here, we propose to characterize diet in a local population of thirteen-lined ground squirrels in order to document dietary variation across seasons, between males and females, and between young and adult. We will use microhistological analysis of fecal samples as well as stable isotope analysis of fecal pellets and hair to characterize diets of squirrels. Our goals are to test hypotheses for the abrupt, transient shift in diet that we previously observed; elucidate patterns of dietary variation across seasons and between adult males, adult females, and juveniles; and test the hypothesis that dietary choices are selective based on nutritional demands at different times of the annual cycle.