Progress 02/01/06 to 01/31/09

Outputs
OUTPUTS: Since the prior report, the main outputs for this project are activities. Activities primarily involved conducting and analyzing experiments. I carried out two main experiments during this reporting period. First, in collaboration with an undergraduate (see participants, I conducted a greenhouse experiment investigating tolerance to herbivory. A plant's ability to tolerate damage may vary with resource availability. In addition, the costs of tolerance may change in resource-limited environments. Using genotypes with high and low tolerance, we examined the effects of intraspecific density on both tolerance to herbivory and costs of tolerance. Density and damage both reduced overall plant fitness, but the effects of density on plant tolerance were more complex. Although tolerance did not differ among density treatments for both asexual and sexual measures of fitness, there was a trend towards greater tolerance in the high-density treatment. Because S. carolinense is a perennial, these effects could become more pronounced if fitness were measured over multiple years. In addition, costs of tolerance were detected only for plants growing at high density. Thus, costs of tolerance appear to be greater for plants growing under more stress. Second, with Nora Underwood and Brian Inouye, I collected and analyzed data from the long-term density manipulation experiment initiated under this grant. We planted an additional 18 experimental populations, and collected data on plants in existing populations. Our analyses so far have focused on three questions. First, how do interactions with other plant species influence the effects of intraspecific density and herbivory on S. carolinense performance In populations with herbivores, damage increased with cover of interspecific competitors. In addition, the effect interspecific plant cover on Solanum size changed from negative to positive in the high and low herbivory plots, respectively. Because herbivory reduces plant size, the increase in damage with greater interspecific cover could change the relationship between interspecific cover and S. carolinense size among herbivory treatments. Second, we asked how density and herbivory affect survival, growth, and fecundity of S. carolinense, and are their effects additive. Although herbivory does not affect overwinter survivorship, it does reduce performance of S. carolinense within a growing season. In addition, the effects of herbivory on plant performance vary depending on the density of S. carolinense: damage affects performance more at low densities, but the greatest overall reductions in plant performance occur at the highest densities. Finally, we directly tested for density functions in vital rates using data from the experimental populations. We found density dependence in transitions associated with the smallest and largest size classes only, and changes in density dependence for at least one transition in high vs. low herbivory populations. Next we will incorporate these density functions into population models that will test the effects of herbivory on equilibrium population size in this weed. PARTICIPANTS: Stacey Halpern (Pacific University) is PI/PD for this project. My role was to oversee, coordinate, and manage all aspects of this project. I designed experiments, collected and analyzed data, supervised student and technical workers, managed the grant, and presented results at professional meetings. I also attended the annual PD meeting, which was held at the Ecological Society of American Annual Meeting in August 2008. John Forte (Florida State University) worked as the technician on the project, partially funded by the subcontract to FSU under this grant. He cared for experimental organisms, set up and maintained experiments, collected and entered data, ordered and maintained supplies and equipment, organized an outreach project (completed in spring 2009), and supervised undergraduate hourly workers. The North Florida Research and Education Center in Quincy (IFAS/University of Florida) was a partner organization. They supplied land for the experiments as well as access to equipment and support with experimental maintenance. Nora Underwood (Florida State University) was a collaborator on the project. In addition to intellectual contributions, she assisted with supervision of student and technical workers and data collection. Brian Inouye (Florida State University) was a collaborator on the project. He made intellectual contributions and assisted with data collection. There were opportunities for training for one technician and one undergraduate student (Kahaili Barrows), who is from an underrepresented group in biology. Barrows (Pacific University) worked as a full-time summer research assistant, partially supported by a fund associated with overhead from this grant. Kahaili, a native Pacific Islander, received training in field research methods and experimental design, including participation in a professional development seminar for summer undergraduate researchers I coordinated at Florida State University. Kahaili helped design, carry out, and analyze the tolerance study described in outputs. She also collected and entered data for the larger field experiment, and helped care for experimental organisms. As a result of her summer research experience, Barrows decided to apply to graduate school in biology, and will be matriculating in an MS program in summer 2009. In addition, the technician received professional development related to the project, including training in data management and analysis that culminated in a presentation at the Southeastern Ecology Conference (see publications). The technician will be starting a PhD program at the University of Florida in fall 2009. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
The primary outcomes for the project thus far are changes in knowledge. We have gained new fundamental knowledge about the biology of herbivore interactions with a noxious weed, Solanum carolinense (see summaries of results in outputs section above), which has been presented at professional meetings and is being prepared for publication. These gains in fundamental knowledge will contribute to our general basic understanding of plant population dynamics and of density effects in plant-herbivore interactions. These knowledge gains may also contribute to developing new methods and approaches for answering questions about pest plant population regulation. In addition, trainees (a technician and an undergraduate student) have gained knowledge and skills that has affected their professional lives. They have learned new techniques for research, and have had opportunities to use those techniques in professional presentations. They have also gained knowledge about their career goals. The technician will begin a Ph.D. program at the University of Florida in fall 2009. His work with this project helped him clarify his strong interests in applied research, and in working with directly with practitioners to develop on-the-ground programs that improve both conservation and people's economic lives. The undergraduate (from an underrepresented group) has switched her career goal from medicine to biology research. After her summer working with this project, she decided to apply to graduate school in biology, and will start an MS program in fall 2009. The knowledge, skills, and experiences both these trainees gained while working with this project have contributed to shaping their desires to pursue science, and to focus on careers or research directions that have conservation and management applications.

Publications

• Fort, J. D., Halpern, S. L., Underwood, N., and Inouye, B. 2008. Does plant competitor identity matter Conference proceedings (abstract), Southeastern Ecology Conference, Tallahassee, Florida, March 2008.
• Halpern, S. L., L.S. Adler, and M. Wink. 2009. Leaf herbivory and drought stress affect floral attractive and defensive traits in Nicotiana quadrivalvis (Solanaceae). Plant Ecology (under review).
• Halpern, S. L. and Underwood, N. (2006). Approaches for testing assumptions about the role of herbivores in plant population dynamics. Journal of Applied Ecology 43: 922-929.
• Burns, J. H., Halpern, S. L., and Winn, A. A. 2007. Do low-quality environments limit the advantages of opportunism in invasive species Biological Invasions 9: 213-225.
• Halpern, S. L. and Underwood, N. 2007. Developing Density-Dependent Models of Herbivore Effects on Population Dynamics in Horsenettle (Solanum carolinense). Conference proceedings (abstract), Weed Science Society of America, San Antonio, Texas, February, 2007.
• Halpern, S. L., Underwood, N. and Bednar, D. 2007. ESA. Plant density affects interactions between Solanum carolinense and its insect herbivores: implications for plant population regulation. Electronic conference proceedings (abstract), San Jose, California, August, 2007.
• Halpern, S. L. and Underwood, N. 2008. Herbivore and density effects on plant performance in Solanum carolinense: Implications for population dynamics. Electronic conference proceedings (abstract), Ecological Society of America (ESA), Milwaukee, Wisconsin, August, 2008.

Progress 02/01/07 to 01/31/08

Outputs
OUTPUTS: Since the prior progress report, the primary outputs for this project are activities working towards the project's goals and outcomes. The main activities involved conducting and analyzing experiments. With the assistance of undergraduate students, technicians, and collaborators, I planted the proposed large density-manipulation field experiment, a primary focus of this project. I have collected, entered, and checked demographic and herbivore damage data from the first full growing season. Analysis of these data (in progress) will address the project's second objective, determining the interactive effects of plant density and insect herbivory on plant vital rates. Data from this experiment also contributes to the project's first objective, characterizing density effects in interactions between Solanum carolinense (Carolina horsenettle) and its insect herbivores. I determined that Leptinotarsa juncta (false Colorado potato beetle) prefer to lay eggs on plants growing at low density in the field. This preference corresponds with results from a prior oviposition experiment in the greenhouse. The relationship between oviposition preference and larval performance is more complex, however. In bioassays of beetle larval growth rates on excised leaves from plants grown at different densities, larvae responded differently to field- and greenhouse-grown plants. Specifically, eating plants grown at high density depressed larval growth rates in the greenhouse but not the field. To see whether density effects could be influenced by induced changes in plant resistance, I completed another greenhouse experiment. This experiment tested the effects of plant density and prior damage on plant quality for L. juncta. As I previously found for Manduca sexta (tobacco hornworm), density but not prior damage affected plant quality (measured as larval growth rate). Finally, I carried out a pilot greenhouse study testing whether short-term effects on L. juncta larval growth rate translate into long-term effects on development time and adult size at eclosion. In contrast to short-term effects, larvae feeding on high density plants grew larger than larvae feeding on low density plants. Manuscripts reporting the results from the experiments addressing objective two are in preparation, and preliminary results have been presented at the Weed Science Society of America's annual meeting in February, the Ecological Society of America annual meeting in August, and the Murdock Undergraduate Research Conference in November. A second activity was mentoring. Two graduate students are pursuing thesis research using Solanum carolinense; they have assisted with this experiment, and are developing their own complementary projects. In addition, three undergraduates worked on this project over the summer, including two women, one of whom is Hispanic. The summer experience contributed to the Hispanic woman's decision to pursue a career in ecology and field biology research. Another summer undergraduate is planning to apply to graduate school in biology after graduation. PARTICIPANTS: Stacey Halpern (Pacific University) is PI/PD for this project. My role was to oversee, coordinate, and manage all aspects of this project. I designed experiments, collected and analyzed data, supervised student and technical workers, managed the grant, and presented results at professional meetings. Joseph Simonis (Florida State University) worked as the technician on the project for most of this fiscal year. He cared for experimental organisms, set up experiments, collected and entered data, and ordered and maintained supplies and equipment. John Forte (Florida State University) worked as the technician on the project for the last few months of this fiscal year. He cared for experimental organisms, set up experiments, collected and entered data, and ordered and maintained supplies and equipment, and supervised undergraduate hourly workers. Maria Sardi (Florida State University) worked as an hourly student lab assistant. She cared for experimental organisms. Amanda Chisholm (Bates College) worked as a full-time summer research assistant. She collected and entered data and helped care for experimental organisms. She also received training in field research methods and experimental design. She wrote a senior thesis at Bates using data from the summer. Katty Paulino (Florida State University) worked as a full-time summer research assistant. She collected and entered data and helped care for experimental organisms. She also received training in field research methods and experimental design. She went on to complete a directed independent study at FSU during the academic year. This experience contributed to career development; she switched from environmental policy to ecology and now plans to attend graduate school and pursue field biology. Joel Weekley (Pacific University) worked as a full-time summer research assistant. He collected and entered data and helped care for experimental organisms. He also received training in field research methods and experimental design. As part of his training, he presented a portion of the summer data at an undergraduate research conference in Oregon. The North Florida Research and Education Center in Quincy (IFAS/University of Florida) was a partner organization. They supplied land for the experiments as well as access to equipment. Nora Underwood (Florida State University) was a collaborator on the project. In addition to intellectual contributions, she assisted with supervision of student and technical workers and data collection. She also presented results at a professional meeting. Brian Inouye (Florida State University) was a collaborator on the project. He made intellectual contributions and assisted with data collection. As noted above, there were opportunities for training for several undergraduate students (Chisholm, Paulino, and Weekley). In addition, both technicians received professional development related to the project, including training in data management and analysis. One technician (Simonis) started a PhD program at Cornell after working on this project.

Impacts
The primary outcomes for the project thus far are changes in knowledge. We have gained new fundamental knowledge about the biology of herbivore interactions with a noxious weed, Solanum carolinense (see summaries of results in outputs section above). The fundamental knowledge gained sets the stage for the acquisition of applied knowledge about managing pest plants with biocontrol agents. It will also contribute to developing new methods and approaches for answering questions about pest plant population regulation. In addition, trainees (primarily undergraduate students, but also technicians and graduate students) have gained knowledge and skills. They have learned new techniques for research. They have also gained knowledge about their career goals. One former technician has begun a Ph.D. program in Ecology and Evolutionary Biology at Cornell University. His work with this project increased his interest in applied ecology, which he hopes to incorporate into his thesis research. One undergraduate (from an underrepresented group) has switched her career goal from policy to ecology research. After her summer working with this project, she is conducting independent research this academic year, will apply for prestigious undergraduate research experiences for summer 2008, and plans to attend graduate school in the future. Other students have had the opportunity to present parts of the project at undergraduate research conferences. The knowledge, skills, and experiences they gained in working with this project have contributed to shaping their desires to pursue science; for some, it has also inspired them to consider careers or research directions that have conservation and management applications.

Publications

• No publications reported this period

Progress 02/01/06 to 02/01/07

Outputs
One goal of this project is to characterize density effects in interactions between Solanum carolinense and its insect herbivores. I am focusing on plant quality, damage levels, and insect behavioral responses. I have completed one greenhouse experiment testing the effects of both plant density and prior damage on plant quality for one herbivore, Manduca sexta. Density but not prior damage affected plant quality in this experiment. Specifically, insects feeding on plants grown at high pot densities had slower growth rates. Studies repeating this experiment for additional herbivores are in progress. I also completed an experiment to determine whether density effects on plant quality carry over to the field (analysis on-going). In the field, plant density (experimentally manipulated) also affected the quantity of feeding by herbivores: damage increased at very high density. Finally, I found that specialist beetles preferred to lay eggs on plants growing at low density, and have collected data on insect movement rates on plants growing at different densities (analysis in progress). These results (in prep, and presented at meetings) lay the foundation for understanding demographic effects of insect herbivores on populations of weedy plants. The second objective of this project is to determine interactive effects of insect herbivory and plant density on plant vital rates. I planted experimental populations in field demography plots in spring 2007, and will collect data related to vital rates starting this May. The data from these demography plots also will be useful in parameterizing preliminary models testing for effects of herbivores in plant population regulation (a third long-term goal not funded under this grant). In addition to the work planned under this project, colleagues and I have completed two related studies. First, my collaborator (Dr. Underwood) and I refined and published analytical methods to determine the herbivore effects on plant demography using density-dependent matrix population models; this methods paper was in a special feature on invasions in the Journal of Applied Ecology in fall 2006. Second, a graduate student in the Underwood lab has initiated studies of induced resistance and genotypic variance in resistance in Solanum carolinense. The information from these studies will provide information that may be useful in interpreting any genotypic or induced responses I observe in our field demography plots.

Impacts
Broadly, this project is developing new methods to evaluate the effects of natural enemies on pest plant populations. These new methods will make it possible to better evaluate control techniques for weedy and invasive plants, including biological control. Pest plant management has enormous economic costs (ranging from crop yield losses to money spent on control strategies), so determining the most effective approaches is important. In addition, some control strategies can have environmental costs, ranging from pesticide contamination to spread of biological control agents to non-target species. By providing new tools for evaluating the effects of a particular control strategy on a target species, this work will help scientists and managers better use limited control dollars and better manage associated risks. Specifically, these studies focus on a noxious weed that can infest fields and orchards, particularly in the southeastern United States. Thus, the results from this work will also provide data useful to understanding and managing this problem plant.

Publications

• Halpern, S. L. and N. Underwood. 2006. Approaches for testing assumptions about the role of herbivores in plant population dynamics. Journal of Applied Ecology 43: 922-929.