Current Research
The overarching goal of my research is to describe and explain mammal diversity and distributions by integrating field inventories, museum specimens, and advanced quantitative techniques. To do so, I build upon a legacy of mammalian community assembly and biogeography research and advance it by quantifying diversity in new ways. Traditionally, ecologists only considered the taxonomic dimension of diversity (e.g., species richness and abundance) to describe spatial and temporal patterns of diversity. However, diversity is multi-faceted, including functional (ecological traits) and phylogenetic (evolutionary relationships) dimensions. Emerging methods that incorporate multiple dimensions of diversity are revolutionizing how ecological patterns and processes are analyzed and interpreted. With this multi-dimensional perspective of biodiversity, the three main themes of my research are (1) understanding patterns of biodiversity and their underlying drivers, (2) informing conservation strategies amid global change, and (3) improving trait-based methods.
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Patterns and Drivers of Biodiversity
Explaining how biodiversity is generated and maintained is a grand challenge in ecology with increasingly urgent implications as we strive to understand the effects of accelerating climate and land use change. To address this challenge, I use cutting-edge methods to quantify community functional trait and phylogenetic composition, which convey not just which species are present but also the characteristics of those species that promote or hinder their co-existence along gradients of abiotic and biotic conditions. Combining this approach with small mammal occurrence data from multi-year field surveys led by myself and colleagues, I developed and tested a novel trait-based framework to determine the drivers of species co-occurrence patterns across heterogeneous landscapes (Kohli et al. 2018, Ecography; video abstract here) and revealed the relative importance of abiotic filters versus biotic interactions in driving diversity patterns along elevational gradients in Nevada (Kohli et al., 2021, Journal of Biogeography). During my postdoc at Ohio State, Marta Jarzyna, Reymond Miyajima, and I expanded the scope of this research to determine the generality of patterns and processes across 49 mountains on 5 continents (Kohli et al., 2022, Global Ecology and Biogeography). We found that rodent functional and phylogenetic diversity patterns along elevational gradients are quite different from the typical mid-elevational peak in species richness. Instead, whether functional and phylogenetic diversity increases or decreases with elevation is tied to how arid or wet it is at the base of a given mountain range. This work opens up lots of exciting new questions and we hope it spurs much more research on the topic! |
Conservation and Global Change
With a more complete description of diversity comes a greater ability to detect, predict, and mitigate organismal responses to environmental change. Much of my research relies on small mammal field surveys to establish diversity baselines and track change over time. For example, I led small mammal resurvey efforts at sites throughout the Snake Range, Nevada including in and around Great Basin National Park. The Snake Range resurvey builds off similar efforts in other Great Basin mountains ranges led by collaborators Rebecca Rowe (University of New Hampshire), Eric Rickart (Natural History Museum of Utah), and others. I reconstructed community composition from historical field notes and specimens to investigate change in mammal taxonomic and functional diversity over the last century, finding a decline in ecological specialists that may be an early warning of impending biodiversity loss (Kohli et al, In Prep). With an intrepid crew of undergraduates from the University of New Hampshire, I also completed the first mammal inventories in unique juniper woodland habitats (locally known as swamp cedars) in Nevada that are the subject of ongoing litigation surrounding water resource development (Kohli et al. 2019, Southwestern Naturalist). These highly unusual low-elevation juniper stands in Spring Valley and White River Valley, NV, first struck my curiosity during our 2015 resurvey field work, so we added them to our 2016 field schedule to see if they harbored pinyon mice (spoiler: they do where the woodlands are dense enough!). To read more about the ongoing legal battle surrounding the groundwater that sustains these ecosystems, see this recent article in the Reno Gazette-Journal. |
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Improving Trait-based Methods
Although the appreciation and application of multi-dimensional biodiversity has grown recently, refinement of a trait-based diversity framework for mammals is much needed. Categorical traits are often employed, but there is a need for traits that capture more of the variation that is present among species. To this end, I have identified several ecomorphological traits that have a demonstrable link to function to provide finer-scale information than traditional functional guilds. I have determined the utility of a suite of craniodental measurements as indicators of diet, relative medullary thickness (RMT) of the kidney as a measure of habitat affinity (mesic-to-xeric spectrum), and hair density as a metric of thermoregulatory ability. Craniodental measurements, hair density, and kidney RMT capture traditional functional group differences for 32 of the most common and widespread Great Basin small mammals while also illuminating meaningful within-group variation. This paper was recently published in the Journal of Mammalogy. More recently, I expanded on the effort to improve trait-based ecology methods by demonstrating, through a series of simulations, that coarse categorical traits inhibit the accurate detection of ecological processes (Kohli & Jarzyna, 2021, Global Ecology and Biogeography). This aspect of my research is the primary focus of much of my current research with students, including both lab and field work to obtain more and better functional trait measurements.
Earlier Research
My previous research focused on using genetic tools to investigate topics including the systematics and biogeographic history of red-backed voles and their relatives (Rodentia, Arvicolinae, Myodini) and the population genetics and management of muskellunge in Ohio (not a mammal, but a very cool fish!). Among other things, this work gave me a strong appreciation for how historical processes influence modern ecological, evolutionary, and biogeographic patterns, a perspective that continues to guide my approach to research.