Date of Completion


Document Type

Honors College Thesis


Animal Science

Thesis Type

Honors College

First Advisor

Dr. Sara Helms Cahan


climate change, Bergmann's rule, Allen's rule, rodents


Over the last century, climate change has resulted in a gradual rise in global temperatures, which has had a significant impact on the functioning of animal ecosystems. In order to cope with the heat, many species have been forced to adjust the way they interact with their environments and adapt to the changing conditions. If climate change is increasing national temperatures, then Bergmann’s rule and Allen’s rule reason that animals are shrinking in size and that their limbs are getting proportionately longer to their body size, respectively, in order to have a higher surface area-to-volume ratio to better disperse heat. To test this hypothesis I collected different length measurements, location data, and the year recorded for 4 rodent species using museum databases. This was done to compare rodent sizes within the past 100 years, with temperature increases ranging from 0.7°F to 2.7°F depending on the state. I have found that the amount of change varies by species, but Peromyscus maniculatus shows the strongest effect as three out of nine states significantly conformed to Bergmann’s rule and to Allen’s rule. Regardless of species, Colorado and California rodents significantly decreased in size – these states were sampled in three of the four species and each time they showed statistically significant decreases in body sizes, except for Rattus norvegicus in California which decreased but not significantly. Those two states also had the largest amount of specimens collected, likely contributing to the ability to be able to find significant differences with the large dataset. Other states also exhibited adherence to Allen’s rule, mostly seen in Peromyscus maniculatus but also in Mus musculus and Rattus norvegicus, although not as much in Sciurus carolinensis – signifying that tail length may serve more crucial functions other than heat dispersion in squirrels. Body and tail sizes determine a lot of important characteristics for animals such as their lifespan, diet, and vulnerability to predation, so any changes in one species may affect those individuals as well as their entire ecosystems.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.