RESEARCH
I’m a plant population ecologist and conservation biologist. My research addresses fundamental questions about how environmental variability shapes life histories and the consequences of those responses for population and community dynamics. In my research I strive to 1) understand the strategies organisms employ to cope with environmental variability, 2) explore their consequences for population and community dynamics, and 3) forecast population trajectories to inform conservation. I usually use plants as model organisms but I love and sometimes use reptiles too. Below I highlight some of my current projects.
If you are interested in joining my lab, please check out the prospective students tab.
If you are interested in joining my lab, please check out the prospective students tab.
Seed heteromorphism in camphorweed (Heterotheca subaxillaris)
I just launched this new project with my move back to South Florida. Camphorweed is a unique seed heteromorphic species in that it grows throughout the southern United States occupying a wide array of habitats from Florida barrier islands to the deserts of southeastern California. In between it grows along roadsides and in disturbed fields. Reportedly it maintains its seed heteromorphism, or simultaneous production of multiple morphologically distinct seeds (achenes), throughout its range.
In this project I aim to determine 1) if this species is seed heteromorphic throughout its range, and 2) if it is, then how the ratios of different seeds change across this range, and finally 3) how the germination ecology of its seeds changes across this range. Through this work I also endeavor to understand this species flowering phenology and other important life history strategies closely tied to its seed heteromorphism. |
A) An image of camphorweed's flowers by Max Licher. B) An image of the camphorweed's seeds (achenes) by Richard Spellenberg. The winged (background) and non-winged (foreground) seeds can be seen in this image.
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The population dynamics of gopher tortoises in South Florida
The gopher tortoises are Florida's only tortoise species and one with a threatened future. This species loves dry upland habitats which are also prized by humans for development. The clash between tortoise habitat and urbanization is fierce in South Florida where most native habitat has been developed. Still a few populations of tortoises continue to persist in this heavily developed region.
Gopher tortoises were my gateway to research as an undergraduate. Now a faculty member, and back at my undergraduate institution, I am studying them again. In particular we have some nice survey data from over a decade ago which we plan to compare to recent surveys to ask questions about this species population dynamics and future in South Florida. Collaborators: Evelyn Frazier, Jon Moore, Steven Whitfield, Adrian Figueroa, Rachel Starck, and Tobin Hindle |
The gopher tortoise (Gopherus polyphemus) lives throughout the southeastern United States and is listed as endangered or threatened throughout most of its range. Photo by Karine Aigner.
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The population dynamics of rare plant species
Rare species are any species that have a very small geographic distribution, or have numerically low numbers throughout their range, or are both geographically restricted and low in number. Interestingly, rare species occur in all biomes across the planet and account for close to half of all species on the Earth. Clearly they are important. As a result, rare species have received a lot of research attention. However, owing to their rarity, these species are difficult to survey and track. In other words, collecting the long term data required to thoroughly study these species is difficult.
The Chicago Botanic Garden collects and manages one of the largest rare plant datasets in the world. Known as the Plants of Concern Program, this data set includes over 20 years of population count information and encompasses more than 200 rare plant species in and around Chicago. Using this dataset I am addressing questions regarding the factors that drive rare plant population dynamics and the efficacy of various management strategies (such as fire) on rare plant recovery and sustainability. Collaborators: Amy Iler, Jeremy Fant, Gretel Kiefer, and Rafael Urbina-Casanova |
Seed heteromorphism in combseed (Pectocarya heterocarpa)
Pectocarya heterocarpa (Boraginaceae) is a winter annual plant that grows throughout arid regions of Arizona, southern California, Nevada, Utah, New Mexico and Northern Mexico. It is seed heteromorphic or simultaneously produces multiple morphologically distinct seeds (nutlets).
Specifically it produces two types of aerial seeds (originating on the upper parts of stems) and one type of basal seed (originating on the lower parts of stems, on or near the soil surface). The aerial seeds can be divided into long seeds, which appear elongated and have bristles (A in image), and winged seeds, which are shorter and have webbed bristles (B in image). In contrast, all basal seeds have severely reduced or no bristles (C in image). Basal seeds also tend to be larger than their aerial counterparts. Ecologists have long speculated that seed heteromorphism serves as a bet-hedging strategy or one that helps plants mitigate unpredictable environmental conditions (e.g. rainfall). Akin to “not putting all of your eggs in one basket,” bet hedging is a counterintuitive strategy wherein organisms spread risk over time by increasing long-term fitness at the expense of immediate fitness. I investigated the germination, growth and reproductive characteristics of the different seed types both within populations (e.g. Tucson, AZ) and across populations (e.g. Arizona and California) to evaluate the function of seed heteromorphism as a bet-hedging strategy. Using a combination of greenhouse, field and growth chamber experiments I showed that P. heterocarpa is hedging its bets and may use plasticity to fine tune this mechanism. Collaborators: Larry Venable, Nick Kortessis, Bethany Farrah, and Gabriel Gudenkauf |
Seed heteromorphism in the Southwest
Offspring heteromorphism is a reproductive strategy in which species simultaneously produce offspring that differ in morphology. It occurs across the Tree of Life but is particularly common among plants, where it is termed seed (diaspore) heteromorphism.
The prevalence of this strategy in highly stochastic environments such as deserts has resulted in the assumption that it serves as a bet-hedging strategy. In this project I summarized the occurrence of this strategy among species in the southwestern United States and northwestern Mexico as represented in local floras. Next, I used the dataset to test the hypothesis that the occurrence of seed heteromorphism increases with increasing environmental uncertainty. Check out the manuscript for more information. Collaborators: Larry Venable, Leo Calle, and Nick Miller |
An ant-plant mutualism in an urban context
Mutualistic relationships between different species are some of the most important drivers of ecological diversity, but it is not fully understood how city landscapes alter these relationships. Many species of plants engage in a mutualistic relationship with ants where they exude sugary nectar from extrafloral nectaries; the nectaries attract and feed ants that then protect the plant by killing and eating other insects on the plant, including potential herbivores. In the Sonoran Desert the barrel cactus Ferocactus wislizeni can potentially form such a mutualistic relationship with many different ant species, including non-native species.
In this study, we compared ant species composition and quality of protection services towards cacti found in urban Tucson, AZ with cacti found on Tumamoc Hill, a rural research station near Tucson, AZ. We assessed protection services through simulated herbivore attacks by first-instar Manduca sexta larva. Once we placed the caterpillars on the cactus we measured the rate of ant recruitment and their effectiveness in removing the caterpillars from the cacti. This project grew out of a course-based undergraduate research (CURE) component that I lead as part of the University of Arizona's introductory ecology course. The research itself was originally started by Dr. Judie Bronstein and her students. Her support throughout the project was instrumental. We collected data across different seasons for two years and found that the mutualism is, ultimately, equally effective in the city as in nature. However, city ants recruit faster in response to herbivore attacks but are less aggressive in their attack as compared to their counterparts occurring in natural habitats. We found only one invasive species on city cacti. This species was not very prevalent (<5% of cacti) and also did not attack or in any way deter herbivores. In the future we hope to compare ant occupation rates of cacti in the city versus nature. Collaborators: Judie Bronstein, Michelle Lanan, Kim Franklin, Candle Pfefferle, Bethany Farrah, Kayla Cuestas, Nehal Bakshi, Caroline Johnston, Finn Allred, and Kaylee Meyers |