Date of Award

Winter 2020

Project Type

Thesis

Program or Major

Natural Resources

Degree Name

Master of Science

First Advisor

Rebecca J Rowe

Second Advisor

Ryan B Stephens

Third Advisor

Adrienne Kovach

Abstract

Rodents often play vital roles in their ecosystems as seed predators and dispersers and can significantly influence the succession and assembly of plant communities. We conducted seed tray experiments to assess the nutritional and environmental factors that influence selection and foraging time of three common rodent granivores: the white-footed mouse (Peromyscus leucopus), the deer mouse (Peromyscus maniculatus), and the southern red-backed vole (Myodes gapperi) for three common seeds: American beech (Fagus grandifolia), red maple (Acer rubrum), and eastern hemlock (Tsuga canadensis). This work was conducted at Bartlett Experimental Forest located within White Mountain National Forest in New Hampshire. Using mixed-effects multinomial logistic models, we identified a strong preference in all three rodent species for American beech seeds, likely due to the combination of its high energetic value and low content of harmful secondary compounds when compared to the other seed types. When beech availability was low, the white footed mouse showed a secondary preference for hemlock, the red-backed vole for red maple, and the deer mouse equal preference for both. Red maple seeds individually contain more energy than eastern hemlock seeds but also contain significantly more harmful secondary compounds. An elongated cecum may allow voles to process these compounds faster and more completely than mice, allowing them to safely forage on the red maple seeds. The resulting divergence in secondary preferences may lessen competition when beech availability is low and facilitate coexistence. Beech was not only the primary seed selected, but its availability was also the primary factor influencing foraging time. For all three rodent species, time on tray increased as beech availability decreased. The impacts of environmental factors on selection and time on tray varied by species and were only significant when beech availability was low. Effects of precipitation and stem density on selection are consistent with predator avoidance behaviors, with larger seeds more likely to be chosen in the rain and under denser shrub cover. The effects of day of year appeared significant but may have been confounded by changing levels of naturally available seeds. Precipitation and luminosity also impacted foraging time. Animals spent less time on tray in the rain, consistent with thermoregulatory behaviors. Animals also spent less time on tray on more luminous nights, consistent with predator avoidance behaviors. Our results illustrate the complexity of rodent foraging behaviors and decisions, with selections being driven by many factors. The most important of these factors is seed quality, though this can be influenced by other factors such as seed availability and environmental changes. These findings contribute to our understanding of rodent foraging patterns and underscore the importance of identifying factors influencing these patterns.

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