Research

I am broadly interested in plant ecology and evolution. I have done research at the population and community levels and am particularly interested in local responses and adaptations to disturbances such as exotic plant invasion, anthropogenic disturbance, and climate change. My research experience is broad but has consistently focused on wild systems that have experienced (or are experiencing) some disturbance and the response of organisms to that disturbance.

Effects of exotic invasive annuals and anthropogenic nitrogen deposition on native desert annual forbs
For my PhD research at the University of California, Riverside, I examined the effects of exotic invasive plants and anthropogenic nitrogen deposition on native winter annuals in California’s deserts. I investigated the effects of nitrogen deposition on soil seed banks in invaded areas of Joshua Tree National Park and found that exotic species tend to dominate the soil seed bank. However, although invasives increased in percent cover with nitrogen additions, this increase was not reflected in the soil seed bank. Furthermore, natives were able to coexist in the soil seed bank and often have more specialized germination requirements than exotics, which may offer a temporal safe-haven for native species persistence over time, especially following drought events.

I also studied the impact of nitrogen deposition on native annual forbs in the field when exotic invasive annuals were removed. The most interesting result of this work is that native annual plants, which have been suggested to be unable to respond to increased soil nitrogen due to evolving in nutrient-poor soils, are able to make use of additional nitrogen when exotic plant density is low. There appears to be a threshold density at which natives and exotics can coexist and both benefit from added nitrogen. However, not all native species experience the same benefits from additional nitrogen and species shifts may occur under long-term nitrogen deposition.

I designed and implemented a greenhouse study to understand physiological responses of native annuals and the exotic annual forb Erodium cicutarium (storks bill filaree) to increased soil nitrogen. The results showed that although natives do respond positively to added nitrogen, there seems to be a plateau at which the benefits cease. However, E. cicutarium demonstrated no such plateau and seemed to steadily increase in biomass as soil nitrogen concentrations increased. This suggests that E. cicutarium may be a more formidable competitor than previously thought.

Desert tortoise health, movement, and head starting
During two years working for the US Geological Survey, I shifted my focus to desert tortoises (Gopherus agassizii) and their habitat. Working with this state and federally listed species gave me the opportunity to expand my understanding of the desert ecosystem by familiarizing myself with a long-lived charismatic herbivore that is intimately intertwined with the health of the plant community. I monitored the health and movement patterns of translocated tortoises, investigated the spatial spread of disease, observed behavior, and evaluated the efficacy of head start programs. I also evaluated habitat suitability and forage availability. These efforts were attempts to better understand the decline of desert tortoise populations, the effects of anthropogenic disturbances and invasive plant species on tortoises and their habitat, and to attempt to increase their numbers in the wild.

Roads as corridors for the invasion of Sahara mustard (Brassica tournefortii)
Studying the movements on exotic invasive plants is important for determining the mechanics of invasions. I used multivariate techniques to explain the invasion of Brassica tournefortii at a Mojave Desert site that had been previously un-invaded. The data suggested that B. tournefortii successfully used to roads to enter and spread throughout the site. It was likely brought into the site along primary roads (paved, high-use freeway) and transported throughout the site along a well-maintained, graded dirt road that spanned the eastern edge of the site. Once B. tournefortii arrived, it no longer required roads to spread throughout the interior of the site. This work is important for informing development planning and weed abatement during contraction near wildland areas.

Evolution of reproductive and life history traits in two closely related taxa in the genus Clarkia
Currently, I am working on a greenhouse study to examine the geographic variation in plant traits that are associated with local climatic conditions in order to predict the effects of climate change on the evolution of plant life history and reproductive traits. I am using two sister taxa: Clarkia exilis (self-fertilizing) and C. unguiculata (outcrossing). For example, if plant populations living at warm, low-elevation sites have evolved to flower earlier than populations living at cooler, high-elevation sites, then we may predict that as the climate warms, all populations will evolve to flower earlier. If the pollinators of these populations do not emerge earlier as well, then these populations will be at risk of failure due to pollinator limitations. I am investigating the variation in a large number of reproductive and life history traits along elevational gradients to determine differences within and between maternal families, populations, and species. Another goal of this research is to determine whether climate warming may increase selective pressure for the evolution of self-fertilization in lieu of outcrossing.

Evolution of wild plant populations in response to climate change
The primary focus of my postdoctoral position is Project Baseline. This is a nation-wide, NSF-funded collaboration that aims to create a research seed bank specifically designed to facilitate future studies of plant evolution in response to environmental change using the resurrection approach. Plant species are already responding to climate change, as evidenced by earlier bud burst, flowering, and arrival of pollinators. However, only in a few cases can we distinguish between phenotypic responses to longer growing seasons and warmer temperatures (plasticity) and genetically based evolutionary change in response to altered patterns of natural selection. The fundamental goal of Project Baseline is to collect seeds that will be the ancestors in future resurrection studies and store them using best practices to preserve viability and genetic diversity. With this valuable resource secured, biologists will be able to grow genetically representative samples of past populations concurrently with modern samples in field and greenhouse experiments, as well as apply both long-established and recently developed genetic approaches to dissect the architecture of genetic change. The scientific goals of Project Baseline distinguish it from other seed banking efforts because they are research based. Since the focus is to test evolutionary predictions, our collection efforts concentrate on wild, relatively widespread, well-studied genera and encompass all functional groups. Seed collection is focused on conservation lands, in order to increase the likelihood of population persistence to enable future biologists to revisit our collection sites.

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