Ecological dynamics and paleoenvironmental change

The rich North American fossil record of mammalian faunas during the Cenozoic presents the opportunity to test hypotheses for species- and community-level response to climate and environmental change over a range of temporal and spatial scales. My research integrates field work and specimen-based approaches with a variety of laboratory and analytical analyses to investigate ecological dynamics during past intervals of warming and landscape change in western North America. My work takes place in the Mojave region of southern CA, the John Day region in eastern OR, and across multiple museum collections. This work has many Collaborators, including several undergraduate research assistants.

Paleoecology of small mammals

Rodents and other small mammals represent over half of extant biodiversity and much of the fossil record. In my research, I employ three primary methods for assessing species dietary ecology and morphological adaptations: stable isotope analysis, 2D-geometric-morphometric dental shape analysis, and 3D-ecometric trait analysis. Recent development in these methods (e.g., in situ laser ablation for isotopic sampling of very small teeth) allow us to investigate small mammals, opening up a valuable, yet underutilized, part of the fossil record. This work is conducted in collaboration with Rebecca Terry, Thure Cerling, David Fox, undergraduate research assistants Molly Moroz and Laura McQuarter, and with the support of the National Science Foundation-Biological Collections Postdoctoral Fellowship. 

Paleoenvironmental reconstructions

While global trends provide important information about broad-scale climate and environmental changes, assessing local ecosystem conditions is key to understanding the relevant drivers of community response. Therefore, I employ multi-proxy approaches to reconstruct past vegetation, moisture conditions, and habitat heterogeneity at the basin scale and in relation to local faunal assemblages. This work is conducted in collaboration with Katherine Loughney, Ethan Hyland, and Jennifer Cotton.

Miocene Barstow Formation, Mud Hills, CA.

In situ laser ablation sampling for isotopic composition of small-mammal fossils spanning the Miocene Climate Optimum in the Crowder and Cajon Valley formations in southern CA.

Mountains as Biodiversity Hotspots through time

Modern mammal diversity across North America follows a striking geographic gradient: areas of high elevation, topographic complexity, and habitat heterogeneity have greater species richness than adjacent lowlands. This topographic diversity gradient is also found in plants, birds, and large mammals across the continents today. As part of an ongoing collaboration with my PhD advisor, Catherine Badgley, my research explores the influences of tectonic activity and climate change on North American rodents over the last 20 million years in order to elucidate the processes underpinning the group's diversification history. Specifically, I assess diversity patterns across spatial scales and in relation to preservation effects.


A central aim of this research is to establish a general framework for assessing the origination and maintenance of diversity gradients over deep time. Merging evidence from the modern-day and fossil records, I aim to answer such questions as: What are the relative roles and rates of speciation, extinction and immigration in generat-ing topographic diversity gradients? How does the evolution of ecological and functional diversity relate to species diversity in dynamic, complex landscapes?

The research is conducted in collaboration with a diverse group of researchers, including geophysicists, landscape and climate modelers, phylogeographers, and landscape geneticists, stemming from a National Evolutionary Synthesis Center (NESCent) catalysis meeting and is supported by a National Science Foundation Research Coordination Grant.  

Present-day diversity for rodents, based on species ranges from NatureServe and compiled at a resolution of 0.1 deg, in relation to elevation. Species richness is highest in the topographically complex and tectonically active western region.

Rodent species richness through time for the Active Region (west of the Rocky Mtn Front Range) and Passive Region (Great Plains and east). Peak mammal diversity for the Active Region coincided with intense tectonic extension and global warming.

Mice-oscapes: Small-mammal isotope ecology in relation to modern environmental gradients and historical land-use change 

Today, species' diets, habitat preferences, and ecological interactions can vary in relation to broad-scale climate and environmental gradients. Likewise, climate, vegetation, and land-use change have had a dramatic impact on the environment and ecological dynamics across the United States over the past 100 years. The stable isotopic composition of small mammals from modern trapping efforts and historical museum specimens offer a window into changing species ecology over space and time.

In collaboration with Jennifer Cotton and Rebecca Terry, I integrate stable isotopic approaches with statistical geospatial modeling to determine the climatic and ecological controls on small-mammal diets. Currently, we are evaluating the stable isotopic composition of biological and environmental samples from the broad array of National Ecological Observatory Network (NEON) sites to

1) assess the interacting effects of climate and landscape change on ecosystems and communities at a continental scale, and 2) generate isotope landscape models – or ‘mice-oscapes’ – to make predictions about how small-mammal dietary ecology has been impacted by four types of land-use change (urbanization, agricultural expansion, deforestation, and grazing intensification). This work is supported by a National Science Foundation Macrosystems Biology Grant.

While much of this work is motivated by questions related to conserving both current biodiversity and importantly, ecosystem function, in a time of pervasive, human-mediated landscape and climate change, the implications for paleoecological research are also significant.

(a) Geographic variation in the carbon isotopic composition (isoscape) of Dipodomys ordii and Perognathus parvus diets across their combined geographic range. Diet values are predicted based on a conditional forest model.  (b) Percent C4-grass abundance within the grass flora derived from the modeled isoscape.

Figure from Smiley et al. 2015.

Dipodomys ordii and Perognathus parvus specimens in the University of Utah Natural History Mammal Collections.

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