Browsing by Subject "Diversity gradient"

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    Evolutionary and ontogenetic patterns of diet and support for tropical niche conservatism in the origins of the latitudinal diversity gradient in clupeiforms (anchovies, herrings, and relatives)
    (2019-08) Egan, Joshua
    The increase in species richness from the poles to the equator is one of the most pervasive and enigmatic spatial patterns of biodiversity. This latitudinal diversity gradient has been intensively studied since it was first described in 1807 and yet there is still no accepted explanation for its existence. My dissertation tested hypotheses about the origins of the latitudinal diversity gradient in the ecologically and economically important clupeiform fishes (anchovies, sardines, and relatives) with a focus on the hypothesized role of niche breadth evolution in the formation of the diversity gradient. My first chapter described the diets of near-shore, marine clupeiforms from Taiwan and compared their diets to co-occurring fish species. My second dissertation chapter identified increasing ranges of prey-size consumption through ontogeny in twelve species of Indo-Pacific clupeiforms. For my third dissertation chapter, I inferred a time-calibrated clupeiform phylogeny and patterns of diet evolution, which revealed a latitudinal herbivory gradient in clupeiforms. My fourth dissertation chapter found support for climate niche conservatism in the origins of the latitudinal diversity gradient in clupeiforms using diet data from chapter one, two, and three and the phylogeny from chapter three. My dissertation research contributes to the development of biological theory and efforts to sustainably manage fisheries.
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    Paleoclimate and mammal paleocology during the paleocene of North America: insights from stable isotopes.
    (2011-08) Rose, Peter Jason
    Paleocene climate and its relationship to mammal ecology and biogeography were examined at continental scale to test for long-term stasis of ecogeographical patterns among mammals and to better understand the effects of climate change on mammalian faunal dynamics. I also investigated local paleoclimatic and paleohydrologic conditions in a region associated with well-preserved fossil mammals to assess the local effects of greenhouse warming and the relationship between paleoenvironment and taphonomy of fossil mammals. The combination of unique and unstable faunas and globally equable climate resulted in complex ecological and biogeographical patterns among Paleocene mammals that contrast from well-structured patterns that exist today. Latitudinal gradients in Paleocene mammal species richness and body size differ from the patterns observed today among extant mammals. Differences between Paleocene and modern biogeographic patterns could be a function of unique Paleocene faunas with distinct ecology, ongoing ecological recovery after the Cretaceous-Paleogene extinction, and/or the diversity and body-size gradients being geologically recent or episodic phenomena and not general features of the geographic distribution of mammals. Sedimentary carbonates found throughout exposures of Paleocene terrestrial formations of the Crazy Mountains Basin, south-central Montana are unlike most other non-marine carbonates described previously in the literature, but may have formed under similar conditions as proposed for some Paleocene carbonates from the Clarks Fork Basin, Wyoming. Select carbonates from both regions contain exceptionally preserved vertebrate fossils and exhibit similar taphonomy.