The role of seed attributes in eastern gray squirrel foraging
Seed attributes are important predictors of rodent foraging behaviors. I examined the role of seed attributes in eastern gray squirrel (Sciurus carolinensis) foraging behavior from an evolutionary, economic, ecological and biochemical perspective. From an evolutionary perspective (chapter 2), I found that squirrel foraging behaviors are influenced by a combination of phylogenetically conserved and evolutionarily labile seed traits, which supports a diffuse coevolutionary relationship between hardwood trees and squirrels and provides indirect evidence supporting the Janzen-Connell and handling time hypotheses. From an economic perspective (chapter 3), I found that eastern gray squirrels are homogenous with respect to their preferences for seed attributes, which is likely due to natural selection favoring caching of specific seeds in the fall. I also provide evidence that squirrels trade between 3 attributes when selecting seeds for caching, which results in a variety of seed types being cached. In contrast, squirrels trade between 2 attributes when selecting seeds for consumption, which leads to fewer seed types being consumed in the fall. From an ecological context perspective (chapter 4), I provide evidence of seed traits interacting with relative seed availability to predict caching. Specifically, when seeds of different caching value (i.e., utility) were paired, relative frequency of availability played a minimal role in predicting seed caching. In contrast when seeds of similar caching utility were paired, relative frequency of availability significantly influenced probability of seed selection for caching. From a biochemical perspective (chapter 5), I identified biochemical and anatomical changes at the cellular level associated with radicle dormancy that serve as a signal of lack of dormancy to eastern gray squirrels. In combination, my dissertation chapters support the existence of complex reciprocal evolutionary effects between hardwood trees and eastern gray squirrels.
Swihart, Purdue University.
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