My dissertation focuses on identifying geographic patterns in the size and shape of spotted hyena and striped hyena skulls and determining if bioclimatic and social variables explain observed patterns. Within the subsequent chapters of this dissertation I investigate geographic variation in spotted hyena and striped hyena skulls using geometric morphometrics and spatial statistics.In chapter one, I examined the relationship between bioclimatic factors, social factors, and spotted hyena skull size to better understand the forces that might underlie geographic patterns of size. Spotted hyenas exhibit slight female-biased sexual size dimorphism. Skull size co-varies with temperature, precipitation, and landcover but more strongly co-varies with population density. The highest densities are associated with the smallest skull size, possibly reflecting a relationship between high population density and access to resources. These findings support the idea that the underlying driver of geographical and ecological rules is access to resources, providing further empirical evidence for the energetic equivalence rule.In chapter two, I investigated the influence of climatic variables and food resources on observed geographic patterns in striped hyenas. Striped hyenas exhibit slight male-biased sexual size dimorphism. There is a strong geographic pattern of size variation in striped hyena skulls with larger individuals found at higher latitudes, as predicted by Bergmann's rule. I found evidence that seasonal climatic variables are better predictors of hyena skull size than annual climatic variables. We did not find evidence to support our prediction that striped hyenas would be larger in areas with higher net primary productivity or increased access to human-provided foods. These findings support the notion that geographic variation in body size is primarily driven by seasonal climatic variables, which is consistent with the seasonality hypothesis.In chapter three, I investigated whether striped hyena skull shape is sexually dimorphic and whether the geographic pattern of skull shape variation supports the historic delineation of subspecies proposed by Pocock (1934). I found no evidence for sexual shape dimorphism in the skull of striped hyenas. While we found considerable morphological overlap between historic subspecies, some parts of morphological shape space were occupied by a single subspecies, suggesting that striped hyenas vary in morphology across geography, but that historic subspecies are not effectively capturing this variation.
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