| People in the Shea-lab |
| Katriona Shea | Associate Professor | 
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| Suann Yang | Post-doc | ||
| Adam Miller | Post-doc | ||
| Rui Zhang | PhD student | ||
| Laura Russo | PhD student | ||
| Britta Teller | PhD student | ||
| Katie Myers | MSc student | ||
| Leah Ruth | Honors student | ||
| Amy Leib | Honors student | ||
| Catherine Cruz-Ortiz | MURE student | ||
| Richard Ashby | MURE student | ||
| Matthew Williams | REU student | ||
| Emily Haner | Undergraduate student | ||
| Mason Heberling | Undergraduate student | ||
| Brosi Bradley | Undergraduate student | ||
| Jennifer Stella | Undergraduate student | ||
| Megan Lundgren | Undergraduate student | ||
| Ben Tabatabai | Undergraduate student | ||
| Carrie Davila | Undergraduate student | ||
| Clayton Costa | Undergraduate student | ||
| Daniel Shin | Undergraduate student | ||
| Maria Stevens | Undergraduate student | ||
| Former members of the Shea-lab | |||
| Olav Skarpaas | Post-doc | ||
| Eelke Jongejans | Post-doc | ||
| Mike Rubbo | PhD student | ||
| Emily Rauschert | PhD student | ||
| Zeynep Sezen | PhD student | ||
| Jessica Peterson-Smith | PhD student | ||
| Tiffany Bogich | MSc student | ||
| Teresina Bailey | Technician | ||
| Emily Leichtman | Technician | ||
| Melanie Northrup | Technician | ||
| Mike Allen | Honors student | ||
| Dave Ruggiero | Honors student | ||
| Gabrielle Hrycyshyn | Honors student | ||
| Cyelee Kulkarni | Honors student | ||
| Zebulon Bartels | Honors student | ||
| Eddie Silverman | Honors student | ||
| Lewis Grove | Honors student | ||
| Laura Warg | Honors student | ||
| Nick Pedatella | Honors REU student | ||
| Paul Chen | REU student | ||
| Rachel Evans | WISER student | ||
| Kristin Gordon | WISER student | ||
| Simone Adeshina | Undergraduate student | ||
| Ann Saghatelyan | Visitor | ||
| Long and happy list | Undergraduate students | ||
Please keep in touch and let us know what you are doing now!
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Some updates:
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| Post-docs |
Suann Yang My research is centered on the intersection between evolutionary ecology and community ecology, especially in the context of colonization. This interest is exemplified in my dissertation research, where I focused on the consequences of community context for the colonization of Vaccinium membranaceum (black huckleberry) at Mount St. Helens.
In the Shea lab, which I joined in September 2006, I am interested in pollinator-mediated interactions of Carduus nutans and Carduus acanthoides. For insect-pollinated plants such as these, pollinator foraging behavior can have important demographic and population genetic consequences.
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PhD students |
Rui Zhang As a new PhD student, I’m interested in how disturbances influence biological
invasion. I’m now doing a little experiment to see how mowing can take
effects on the growth and fecundity of exotic species Carduus nutans and
C. acanthoides. I expect interesting ‘mowing effects’ resulting from
the interactions among disturbance frequencies, disturbance intensities and
plants’ life stages. This will improve our knowledge of how disturbance can
be used as an effective tool for invasion control..
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MSc students |
Katie Myers My research with the Shea lab concerns external factors that affect seed dispersal in Carduus nutans and C. acanthoides thistles. The factors I am most interested in at the moment include environmental factors such as temperature and humidity, floral predation from the larvae of the specialist weevil Rhinocyllus conicus, and changes in the wind profile throughout a thistle patch.
I spent last summer working on my research through funding provided by a Research Experience for Undergraduates grant from the National Science Foundation. Currently, I am processing plant material collected during this field season and analyzing the data. In time, I hope to write up my findings as part of an honors thesis and continue my research to build towards a masters thesis in ecology.
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Honors students |
Leah Ruth I am a second year Honors and WISER student. I am majoring in Horticultural Science with a minor in Biology. I worked on other lab member's projects during the spring semester '06, and this fall I am starting a project of my own. I will most likely be working on a Carduus nutans and C. acanthoides soil seed bank project and/or a leaf nutrient analysis project that studies leaves produced by thistles with varying degrees of stress. I am also hoping to spend the summer '07 semester in State College, potentially working on my project and developing my thesis paper.
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Amy Leib As an undergraduate student in the Shea Lab, I have spent the past year (Spring 2006 through Fall 2007) working on other lab members’ projects. This semester (Spring 2007), I am starting to work on my own project that could potentially develop into my honors thesis. I am a sophomore majoring in Biology and minoring in History and am looking forward to putting a project together that will allow me to focus on both of these interests. I would like to compile more information about the history of Carduus nutans in North America over the past 160 years. Specifically I will try to resolve whether C. nutans was introduced in one location or in several locations over different periods of time. In addition, I would like to determine whether the history of the invasion of C. nutans is correlated to events in human development in North America.
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MURE students |
Catherine Cruz-Ortiz |
Richard Ashby |
Former Post-doc |
Olav Skarpaas I am interested in population ecological theory and its application to environmental management problems. Three of the major man-made environmental problems of our time are climate change, land use change and biological invasions. I do research that is relevant to all three (see below), but my main focus as a postdoc in the Shea lab (2003 - 2005) was invasion. Ecological theory is still largely unable to predict the speed and spatial patterns of spread of invasive species, partly because of insufficient knowledge about the shapes of dispersal kernels. In collaboration with Dr. Shea (and others) I am developing models to predict the rates and patterns of spread of the two invasive thistles Carduus nutans and C. acanthoides on a range of spatial scales. The empirical basis for the modeling is an array of population biological studies conducted by the Shea lab. I am responsible for wind dispersal studies aimed at measuring and modeling dispersal kernels. I am also interested in the ‘inverse’ of the invasion problem: conservation of threatened species. In previous (M.S. and PhD) and ongoing research I investigate the links between habitats and vital rates in lab and field studies, and model the local population and metapopulation dynamics of rare plant species in fragmented landscapes. Most of this work (carried out in collaboration with people at the Universities of Oslo and Tromsø, Norway, and the Norwegian Institute of Nature Research) is focused on two declining plant species in Norway, Mertensia maritima and Crepis praemorsa. These species are affected by climate change (M. maritima), land use change (C. praemorsa), and their interaction. Olav moved to a postdoc at the University of Oslo, Norway, and now works for NINA in Norway. He is still actively involved in research in the Shea lab. |
Eelke Jongejans My main interests are in processes at the plant level, and their impact on population dynamics, both at the local and at the landscape scale. In plant ecology research I prefer a combination of field, experimental and modeling studies.
In the Shea lab I studied the spatial population dynamics of invasive thistles in both their native range and different invaded ranges, using local and spatial matrix models and integral projection models. I am currently conducting this type of studies at the Radboud University Nijmegen (more info), while continuing to be involved in several projects in the Shea lab. |
Former PhD students |
Mike Rubbo My research focuses on understanding the impact of variations in system level processes on community dynamics. Specifically, I am interested in the influence of variations in the input of allochthonous carbon to food webs that are based primarily on detrital pathways. In order to assess the importance of external inputs of carbon and nutrients to communities, I utilize temporary forest ponds as a model system. These ponds are heterotrophic systems that rely principally on leaf-litter from the over-story vegetation for the major input of organic carbon. Ephemeral ponds are used primarily as breeding sites for amphibians and invertebrates. The amphibians that breed in these ponds exhibit complex life cycles (CLCs), with juveniles emigrating from natal ponds shortly after metamorphosis. The successful recruitment of juveniles from these ponds is extremely stochastic. I am interested in how variations in factors such as the inputs of carbon and nutrients influence species interactions, and ultimately amphibian recruitment. If the performance of a species’ is altered in concert with a change in one or more of these factors, this species’ fitness may be altered through such means as a shift in competitive ability, or through a change in its vulnerability to predators or pathogens. Mike moved to Virginia Tech as a postdoc with Dr. Lisa Belden and works now for an environmental consultancy. |
Emily Rauschert
I am focusing on understanding the mechanisms behind plant species invasion, and how this can lead to improved management of highly invaded systems. I am also interested in the role that humans play in the spread of invasive species. My work aims to combine modeling, experimental and observational techniques. I am currently pursuing a post-doctoral position with Dave Mortensen in the Weed Ecology Lab in the Department of Crop and Soil Sciences at Penn State. We are focusing on quantifying the mechanisms behind the rapid invasion of an invasive grass, Microstegium vimineum. Evidence from dispersal experiments clearly demonstrates that Microstegium spreads very slowly unaided; clearly human-mediated dispersal is largely driving the invasion of this species. We are focusing our initial efforts on the role that road maintenance has on spreading Microstegium propagules. This research, which is in collaboration with the Center for Dirt and Gravel Road Studies, has been funded by the National Research Initiative of the USDA Cooperative State Research, Education and Extension Service, grant # 2007-02917. I recently finished modeling the spatial spread of Microstegium, using data from a three year experiment on establishment in different habitats. I am also working with data from a large-scale survey of multiple invasive species in a forest along the Pennsylvania-Maryland boarder. The aim of this work is to identify the factors associated with invasive species presence, and then to predict areas where invasive species are more likely to occur, in order to focus management efforts. My dissertation work focused on interactions between Carduus nutans and C. acanthoides, two congeneric invasive thistle species. It was hypothesized that their observed spatial segregation was due to interspecific competition. I developed spatially-explicit simulation models of competitive interactions between these species at both the landscape and the field levels, to explore the range of behaviors predicted, and compared these to the results of a series of response-surface experiments on competition between these species. In order to understand natural patterns of co-occurrence, I quantified the thistle distribution patterns at two resolutions: the regional level in an area of overlap, and the field level in four fields of natural co-occurrence. I examined their interactions with the existing vegetation in two ways: by quantifying their vegetative associations in four fields of co-occurrence, and by experimentally examining their germination and establishment response to microsite characteristics. Combining the results from these different approaches demonstrates that the observed distributional pattern is unlikely to be due to interactions between thistle species, and is more likely due to their spread history and their difficulty competing with established species. Katriona Shea, Stephen Roxburgh and I reviewed the mechanisms underlying the intermediate disturbance hypothesis: Shea, K., S. H. Roxburgh and E. S. J. Rauschert (2004). "Moving from pattern to process: coexistence mechanisms under intermediate disturbance regimes." Ecology Letters 7(6): 491-508. |
Zeynep Sezen As a graduate student in the Shea lab, I am interested in the effect of the local spatial distribution of the invasive musk thistle Carduus nutans on the population dynamics of its biocontrol agent Rhinocyllus conicus. This seed feeding weevil has commonly been used to control non-native thistles such as musk thistle and plumeless thistle with variable success. The weevil has also been reported to establish on non-target native thistles, therefore these alternative hosts may be a possible reason for the lack of success in some control programs. Initially, I am looking to see how the patch size and density of the thistles affect the oviposition and adult density of the weevil. Through a better understanding of the patch preference I hope to further identify factors that limit or facilitate weevil establishment. I am also interested in the link between community diversity and invasions and have a small side project looking to see how the presence or absence of the musk thistle relates to differences in community composition. |
Jessica Peterson-Smith My research interests are focused on plant community dynamics, scaling up to ecosystem processes and down to population ecology. I spent 1 year in the Shea lab (September 2004 - July 2005). I am interested in using community ecology theory and modeling techniques to study the establishment and success of invasive thistles. Additionally, I am interested in the link between the spread of invasive species and changing environmental regimes and plant community composition resulting from land-use transformations and disturbance. My previous research work for my M.S. degree included studies of natural plant communities in tidal freshwater wetlands, specifically investigating the composition, spatial distribution, and controls on germination of seeds in the soil seed bank, as well as factors explaining varying levels of species richness in these communities. Most recently, I was employed as a project manager with a large research team based at Penn State testing a wetland classification and functional assessment scheme in forested wetlands of the Appalachian Mountains ranging from Virginia to New York.
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Former MSc student |
Tiffany Bogich
I completed my MSc in the Shea Lab in August 2006. My work in the Shea Lab was focused on the optimization of monitoring and management decisions for invasive species, using the invasion of the gypsy moth Lymantria dispar into North America as a case study. Currently, I am in my second year as a PhD student in the Conservation Science Group at the University of Cambridge, funded by the Bill & Melinda Gates Foundation. My work is centered on gathering global, regional, and empirical evidence for the Species Area Relationship as used to predict species' extinction from habitat loss and then developing a mechanistic model to explain the relationship of habitat loss to extinction risk across spatial scales. My current email address is: tlb24@cam.ac.uk
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Former Senior Research Technologists |
Teresina Bailey I was the first technician in the Shea lab (June 2001-September 2002). My interests are Geography of Nutrition and Urban Poverty (my work-in-progress Masters thesis), urban gardening, herbal medicine, and a host of earth sciences related topics…can’t you tell? I look like a thistle!! I am pursuing a career in grassroots community organizing, social activism, and music. Look out for The Manhandlers! Teresina now works for the Urban IPM group based from the Department of Entomology. |
Emily Leichtman (née Phillips) I began working in the Shea lab in the summer of 2002 (till July 2003), taking over from the unparalleled Teresina Bailey (see above) as senior technician. I manage several of Dr. Shea's on-going experiments, coordinate the activities of our undergraduate assistants and perform a variety of other tasks in the field and in the lab. I am eager to gain more experience with terrestrial ecology and with modeling and have initiated a project examining the effects of Carduus nutans seed size on germination time. In collaboration with grad student Zeynep Sezen, I am also planning a project to model C. nutans seed head production as it relates to plant size at the beginning of the spring growing season. Before joining the Shea lab, I completed my M.S. in Ecology here at Penn State. I am currently preparing a manuscript of my masters work, a study of fish populations as indicators of acidified streams, for publication. In general, I am interested in the response of populations and communities to disturbance. Emily now works for NSF |
Melanie Northrup I joined the Shea lab in July of 2003, taking over for Emily Phillips as the senior research technician. I manage Dr. Katriona Shea’s on-going experiment involving two invasive thistle species (Carduus spp.). I also coordinate the hiring and scheduling of activities of a team of undergraduate student workers. I am interested in learning more about this facet of ecology and experimental design of large-scale experiments. I will also be involved with some of the statistical analyses associated with the project. Before joining the Shea lab, I completed my M.S. in Forest Management here at Penn State. I developed a classification scheme of forest understory communities and focused on the relationships between these communities and oak regeneration. I am currently in the process of revising a manuscript of my work for publication. I will soon start work on a project for the Forest Service in Pennsylvania, in which I will analyze statewide forest inventory data in collaboration with a PhD student in the Forestry Department at Penn State. Melanie has now moved to the lab of Dr. Claus Holzapfel at Rutgers. |
Former Honors students |
Mike Allen I studied spatial distribution patterns, particularly those of invasive species. My thesis project bolstered a personal interest in GIS technology and spatial mapping. Under Dr. Shea’s guidance, I developed a research project aimed at examining the distribution of our two study species, the musk and plumeless thistles, over a range of Pennsylvania and at broader spatial scales. My field research involved an intensive driving survey of a section of PA during the summer of 2002. Mike graduated in May 2004 and moved to the PhD program at Illinois under Dr. Carla Caceres. more info |
Dave Ruggiero My honors thesis, examined the various environmental factors that affect the germination rate of our two thistle species (Carduus nutans and C. acanthoides). Earlier research has suggested that thistle germination is a strong predictor of an individual plant's survival later on. If thistles can get established early on, they're very difficult to eradicate.
Therefore, I asked: what environmental factors are conducive to thistle germination, and what factors inhibit it. Specifically, my research examined the effects of: * Maternal habitat: do better conditions for the parent plant result in better seeds? * Soil moisture: does rainfall affect germination? * Microhabitat size: competition greatly influences germination success, but how close must competitors be before they have an impact? Dave graduated in May 2004 with a B.S. in Environmental Resource Management, and honors (and a minor) in Biology. He moved to the graduate program at Stonybrook with Dr. Jessica Gurevitch in the fall of 2004. |
Gabrielle Hrycyshyn I worked with Dr. Hauge at the Hazleton campus on a mark-recapture study of 4 species of indigenous turtles (Pseudemys floridana penninsularis, P. nelsoni, Sternotherus odoratus and S. minor minor) in a Wekiwa Springs State Park, Apopka, Florida. By the time I graduated in May 2004 I had gone to the site 6 times over 4 years. I used the data collected from these outings to determine the population size of these species, as well as estimates of growth, survivorship and recruitment. I worked with Dr. Shea here at University Park, utilizing the data collected in the field and estimates from the literature, to create a theoretical population matrix model for these species to see how their populations might respond to different water regimes. As the study site is within the Orlando metropolitan area there have been predictions that the water level in the spring will be halved within the next 20 years due to increased water consumption. The models provide a glimpse of what might occur and can hopefully be used to help managers who must keep these contingencies in mind. I was a member of the Shea Lab for two years, working with the thistles. In addition to helping with the experimental plots, I have been fortunate to be involved in the research of most of the graduate students and postdoc: Emily, Zeynep and Olav. These experiences included GPS surveys, road surveys, thistle head dissections, seed dispersal studies and finding suitable field sites. My main lab-oriented task during the off-season was maintaining the lab reference library in EndNote, 3200 references and counting! Gabby moved to start her Masters research at the University of Florida in Gainesville with Dr. Karen Bjorndal in summer 2004. |
Cyelee Kulkarni Modeling of microparasite dynamics has been carried out for numerous systems, however, a detailed analysis through the use of mathematical and computer modeling of macroparasite systems is still relatively rare. The study of macroparasites, particularly helminthic parasites, including the class of digenic trematodes, is of great importance to both humans and amphibians since trematodes cause hundreds of cases of human diseases each year and have also been linked with developmental abnormalities in amphibians. Understanding the ecological dynamics of such systems should lead to improvements in management. In my thesis I developed and analyzed alternative life cycle models for a generic amphibian-trematode system, motivated by species complexes found in central Pennsylvania. Such systems usually include a second intermediate host (a snail) as well as a definitive host (e.g. a fox or snake) though often the definitive host is unknown.
Cyelee moved to graduate studies at the University of Pennsylvania. |
Zebulon Bartels I joined Dr. Shea's lab in the summer of 2001 as a part-time research assistant. Through the summer and fall I helped Dr. Shea set up and run the invasive thistle experiment that continues to be the lab's biggest project. In the fall of 2001 I began my own experiment within the lab. I tested the germination and growth of two similar thistle species on differing soil textures and under different watering regimes. Rather than using field soils of a few soil textural classes, as is commonly done for such tests, I attempted to formulate all twelve of the textural classes by mixing pure quantities of the three soil particle types: sand, silt, and clay. I used my work in Dr. Shea's lab as a basis for writing my honors thesis.
I majored in Agroecosystems Science. After a volunteering for a year and going to graduate school I plan to return to my father's farmland and start an organic farm, where I hope to do on farm research in cooperation with research institutions. Two of my main non-academic activities are classical guitar performance and activism for peace and justice. |
Eddie Silverman As an Honors student here at Penn State, I started working in the Shea lab in the Fall of 2004. I have worked most closely with Olav Skarpaas. The first chapter of my thesis will focus on the relationships between seed characteristics, seed dispersal, and seed germination rates. In the future I will plan a larger project to quantify the effect of animal feeding on the thistles both as seeds and seedlings. Little is known about what happens to seeds between the time when they land on the ground to the time when they germinate. The summer of 2005 will be dedicated to this project, to hopefully fill in this gap of information in the thistle life cycle. It will be interesting to see the effect of seed predation on the thistle populations. Eddie graduated in May 2006 and moved to medical school at George Washington University |
Laura Warg My study aims to use genetic information to track the invasion of Carduus nutans and to relate that information to invasion patterns proposed by existing scientific literature. Samples from across the United States, as well as the UK, Netherlands, and France, have been collected and cultivated to yield plant material from both the native and invaded ranges. In a partnership with the dePamphilis lab, I’m conducting a genetic study of variable regions in C. nutans DNA. This study involves isolating DNA from leaf samples, locating polymorphic regions, amplifying these regions, and then sequencing them. The sequences will help to clarify the invasion geography and timeline of C. nutans, as well as supplement a larger phenotypic study being conducted by the Shea lab. Originally Laura was interested in field work, but became keener on the genetic studies. Her field research in the Shea lab focused upon the effect that insect herbivory has upon thistle seedlings. Field studies in Fall 2005 involving both C. nutans and C. acanthoides were designed to provide information on the extent of insect damage by comparing insecticide treated plants and non-insecticide treated plants. The aim was to replicate this experiment, as well as add a study of the insects present in the area. With the use of pitfall traps, the species feeding upon the thistle seedlings could be captured and identified. Together these two investigations should add some insight into this early period of the thistle life cycle. |
Lewis Grove My Honors research in the Shea lab consisted of data analysis of a data set of avian census results from the Kurupukari region of Guyana. The data was collected in 1992 by Dr. Shea and associates. The data was summarized and analyzed using standard survey technique statistical methods. This represents a comprehensive and unique data set for the region and can serve as the basis for future expeditions. |
Former REU students |
Nick Pedatella The goal of my Summer 2005 study was to examine how changes in specific weather conditions, such as humidity, turbulence, and temperature effect the abscission process of Carduus acanthoides and Carduus nutans within a controlled environment. How flower heads at different stages of development react will also be examined.
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Paul Chen To optimize management of invasive Carduus thistles, seed dispersal needs to be quantified in natural populations. I tried to determine if mechanistic wind dispersal models could accurately predict seed dispersal patterns in natural populations. During the summer of 2004, seed traps were used to capture seeds at four different road sites and pastures. Wind data were collected from weather stations nearby. Now, empirical dispersal kernels and the outcome of mechanistic models will be compared
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Former WISER students |
Rachel Evans Rachel joined us through the WISER program. She was an Honors student majoring in Environmental Resource Management.
Rachel spent a semester in Montpellier, France. She worked on policy issues in the lab and then did an Honors thesis elsewhere on law and the Endangered Species Act. She will start at Harvard Law in Fall 2007.
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Kristin Gordon I am an undergraduate student member of the WISER program. I am working on a research project with Zeynep Sezen on the chemical ecology of Carduus thistles and their insect herbivore, the thistle head weevil. We hope to determine whether the volatiles released by thistles, as a result of weevil attack, attract other weevils and how weevils respond to these volatile chemicals in general. Although it is not within the scope of this study, we may discover whether or not a weevil releases pheromones that are detected by thistles and induce a response in the plant as well.
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Former Visitor |
Ann Saghatelyan |
Former Undergraduate student |
Simone Adeshina I am a senior majoring in Biochemistry and Molecular Biology. I am interested in other areas of science, which is why I came to do lab work in Shea lab. I have worked with Zeynep on her project on the search strategy and oviposition of the specialist weevil herbivores, Rhinocyllus conicus. I investigated the interaction of resources and competitors with the specialist herbivore on mowed plants.
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Former Undergraduate students
