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Bachelor of Arts
Sciurus carolinensis, Sciurus carolinensis-morphological variation, Sciurus carolinensis-subspecies differences, Eastern grey tree squirrel, Museum data, Bergmann's Rule, Allen's Rule, Climate change, Phylogeography, Latitudinal gradients, Sciurus carolinensis carolinensis, Sciurus carolinensis extimus, Sciurus carolinensis fuliginosus, Sciurus carolinensis hypophaeus, Sciurus carolinensis pennsylvanicus, Gray squirrel-Morphology, Gray squirrel-Climatic factors, Morphology, Phylogeography
In the past 150 years, the eastern gray squirrel, Sciurus carolinensis, has had to adapt to the rapid urbanization of the United States. Within that time, many specimens of the squirrel have been collected and preserved in museums. As a result, large research collections exist. One goal of this investigation was to determine how museum data can and cannot be used to conduct investigations of body size of well-studied organisms. Since data have been collected for this species over the past century and a half, this study also sought to study the effects of year as a proxy for climate change on body size in S. carolinensis. Lastly, the effects of latitude on body size were examined in S. carolinensis to evaluate the validity of Bergmann’s and Allen’s rules within this species and taking subspecies into consideration as a confounding variable.
Information from 1928 specimens was collected from 27 museums and used to calculate General Linear Models in Minitab 17 that showed the relationships between body measurements and variables of sex, latitude, subspecies, and year. The results suggest that body size increases and that relative tail length decreases with latitude in S. carolinensis in accordance with
Bergmann’s and Allen’s rules, respectively. In addition, female squirrels have higher relative weights than males at all latitudes. However, when examining two subspecies, latitude has a stronger correlation with body size in the southern S. c. carolinensis than in the northern S. c. pennsylvanicus, suggesting that mechanisms other than temperature may be responsible for the latitudinal gradient. In addition, only the relative tail and ear lengths of S. c. carolinensis show a correlation with latitude. Northern subspecies, however, are significantly larger than smaller subspecies. Due to the confounding nature of the relationship between year of collection and locality as well as to accommodate varying degrees of climate change with latitude, the effects of year on body size were evaluated within three distinct latitudinal bands. Over time, squirrels at high latitudes (40-43˚N) demonstrate an increase in body size and a decrease in extremity length.
Squirrels at mid (35-38˚N) and low (29-32˚N) latitudes demonstrate a decrease in body size over time, and those at low latitudes also demonstrate an increase in relative hind foot length with time. The results of this study augment prior literature regarding changes in body size in rodents with time connected with climate change. Use of museum data yielded unexpected results. First, data had a substantial gap between 1900 and 1925, perhaps partially as a result of World War I. Secondly, although many specimens were identified to subspecies, 769 were not. These unidentified specimens were primarily geographically clumped in two areas. One clump corresponded to the range of S. c. pennsylvanicus, and the other did not correspond to the range of any of the five subspecies as dictated by the museum data. The latter group of unidentified specimens are hypothesized to either be an undescribed subspecies or a hybrid of S. c. pennsylvanicus and S. c. carolinensis.
Fielding, Isabella Marie, "A broad-based investigation of body size of Sciurus carolinensis in space and time" (2017). Honors Project, Smith College, Northampton, MA.
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