My research combines field, laboratory, and studies to understand ecological responses to environmental change in the past, present, and future. My work typically includes some stable isotope geochemistry for diet and environmental reconstructions in combination with other indicators of diet, physiology, movement, and environment.
Rodent Diet Isoscape | Diet Mixing Modeling | Diet Ecology and Population Dynamics | Interspecific Competition
Paleocommunity diets over 4 million years | Quaternary Paleoclimate Reconstructions
Fluid Preservation Effects on Stable Isotopes | Life History Traits of Mollusks from 39 MA
Paleocommunity diets over 4 million years | Quaternary Paleoclimate Reconstructions
Fluid Preservation Effects on Stable Isotopes | Life History Traits of Mollusks from 39 MA
Carbon isotopic variability in modern rodents in the Great Plains, USA for interpreting diets of fossil rodents
Collaborator: David L. Fox (University of Minnesota)
Species' diets respond independently from one another across the landscape. When grouped by diet category, granivore diets diverge from folivore diets as the proportion of C4 plants increases on the landscape.
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Small Mammal Diets in a Short-Grass Prairie during a Short-term Climate Event, Meade Basin, Kansas
Collaborators: David L. Fox (University of Minnesota), Kena Fox-Dobbs (University of Puget Sound)
Climate predictions for much of the Great Plains includes increased frequency of severe drought. Understanding how these prolong periods of drought will influence dietary ecology of mammals will be important for understanding community dynamics necessary for making informed conservation decisions. We characterized the food resources partitioning by a small mammal community in a short-grass prairie located in southwest Kansas. We used stable isotope mixing models to estimate dietary contributions of various invertebrate and plant food resources into rodent diets. Ord's kangaroo rat (granivore) utilizes the most C4 resources via seed predation. The Northern Grasshopper mouse and the Deermouse both have highly variable diets with significant consumption of invertebrates. As precipation increases over four years, C4 derived resources become a greater source of food.
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Diet Ecology and Population Dynamics of Rodents in Northern Minnesota
Collaborators: David L. Fox (University of Minnesota), MDNR (Minnesota Department of Natural Resources), and the 1854 Treaty Authority
I am collaborating with state government and tribal authorities to investigate the spatial variability among small mammal diets and populations in Northern Minnesota. Annual small mammal surveys by the 1854 Treaty Authority aims to characterize small mammal populations that serve as food resources for fur bearing mammals and birds of prey. We are analyzing the diet ecology of rodents in relation to population dynamics, inter-specific competition, and environmental factors. Habitats most commonly surveyed are aspen parklands, coniferous forests, mixed broadleaf forests, and a few grassland locations. These data will also serve as the C3 end member environment in comparison to the grasslands of the Great Plains. Additionally, these data will help interpret similar data from the fossil record focused on identifying the dietary responses of small mammals at the edge of the Laurentide Ice Sheet.
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Fourteen-Year record of Small Mammal Diets in Northeast Minnesota
Collaborators: John Munson* (University of Minnesota, Undergraduate), David L. Fox (University of Minnesota), Martha Minchak (MDNR)
There are few long-term records in North America of small mammal surveys that include diet analysis. We have partnered with one MDNR survey near Duluth, MN to evaluate small mammal ecology over 14 years. This unique dataset offers an opportunity to compare small mammal ecology with population dynamics, climate change, and food availability. We are currently analyzing hair and potential food items for stable isotopes to reconstruct diet over the course of the study and compare to other populations from across the region.
Small Mammal Diets Through 4 million Years of Environmental Change in the Meade Basin, southwest Kansas
Collaborators: David L. Fox (UMN), Kena Fox-Dobbs (U. of Puget Sound), Robert Martin (Murray State U.)
We are testing whether abiotic or biotic factors influence the evolution and community turnover documented in small mammals found in the Meade basin in southwest Kansas. The record focuses on the a 4 million year diet record indicated by stable isotopes signatures preserved small mammal teeth and analyzed via laser ablation. These stable isotope data will provide insight into how small mammals partitioned food resources on the landscape and what their dietary responses were to environmental change.
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Reconstructing Climate Using the Area of Sympatry of Species' Geographic Ranges
Collaborators: David L. Fox and David Polly, University of Indiana
Geographic distributions of extant terrestrial mammals are determined in part by the climatic conditions tolerated by constituent populations, which is a measure of the ecological niche of the species. Assuming niche conservatism, past populations of a species should have had the same climate tolerances as extant populations, thus past biogeographic distributions for extant species might be used to estimate paleoclimate quantitatively. The Quaternary fossil record of small mammals in the Great Plains is a good test case for this approach as many extant species have multiple occurrences over the last million years. We have developed a GIS based method that uses modern species ranges and environmental parameters that relate quantitatively to extant species distributions in North America (e.g., mean annual temperature or MAT and mean annual precipitation or MAP). We assess reliability of this method by varying the number of extant species (20, 15, 10, 5, 3 species) for a given location used to determine range overlap and the distribution of climate variables in the area of overlap then compared estimated and known values.
Stable Isotopes, Tissue Assimilation, Enrichment Values
Collaborators: David L. Fox (University of Minnesota) and Kena Fox-Dobbs (University of Puget Sound)
The isotopic signatures of a consumer’s tissues are derived from isotopic signatures of the consumer’s diet. However, not all tissues record diet over the sample time span nor the same aspect of an individual’s diet. For example, dietary proteins are directly routed towards synthesizing a consumer’s proteins such as hair and collagen. Alternatively, carbonate within bioapatite (teeth and bones) records diet over the growth of a tooth and provides a more integrated indication of an individual’s overall bulk diet. My research has begun to address these differences by analyzing tissues from the same individual in order to calculate stable isotope enrichment factors between tissues. Determining the relationship between tissues will provide a complete analysis of diet, but also provide a transfer function between tissues in order to compare studies using differing tissues. Furthermore, these paired analyses will provide insight into metabolic processes and nutritional needs for organisms.
Fluid preservation in formalin and ethanol is one of the main forms of preservation in modern vertebrate collections around the world. These specimens allow researchers to re-examine specimens in their original form as opposed to skin and skeleton specimens that have been deformed or cleaned of any soft tissues. Stable isotopes are a way to reconstruct an individual's diet, environment, and habits, but researchers typically utilize skeletons and skins avoid the use of fluid preserved specimens because of the unknown effects of fluid preservation on stable isotope compositions. Previous work has focused on the isotope compositions of soft tissues and found that formalin greatly influences the composition. Here, we are evaluating the effects of fluid preservation on bioapatite, collagen, and hair which are relatively stable tissues and readily used in reconstructing ancient ecologies. We have ongoing experiments where specimens were subjected to different fluids (formalin, ethanol, formalin:ethanol mixture) and tissues were sampled over time to record any isotopic changes if they occurred.
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Rapid Growth Explains Large Size of Mollusks in the Eocene Gosport Sand, United States Gulf Coast
Collaborator: Linda C. Ivany, Syracuse University
The late–middle Eocene Gosport Sand of the United States Gulf Coastal Plain preserves a spectacularly dense accumulation of fossil mollusks in which shells appear unusually large in comparison to congeners in adjacent units. Gosport Sand individuals are larger than those in adjacent units. We used sclerochronology and stable isotope geochemistry to assess growth trajectories for twelve lineages common to the three formations. Isotope analyses of microsamples collected along the ontogenetic trajectory reveal seasonal temperature changes, providing a chronometer for growth. Size-age data indicate that, while life spans vary somewhat among the three units, Gosport Sand taxa almost universally grew faster than those in the two adjacent formations. While growth rate can be enhanced by several factors, we hypothesize that rates of primary production were higher during deposition of the Gosport Sand. Ba/Ca ratios along the growth trajectories of shell carbonate exhibit spikes in Gosport Sand mollusks that are indistinguishable from those observed in modern shells that accrete in high productivity settings.
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Haveles, A.W. and Ivany, L.C., 2010, Rapid Growth Explain Large Size of Mollusks in the Eocene Gosport Sand, United States Gulf Coast, PALAIOS, v. 25, p. 550-564. Paper
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