Pati Vitt, Ph.D.
Susan and Roger Stone Curator, Dixon National Tallgrass Prairie Seed Bank
Teaching and Research Affiliations
Adjunct Assistant Professor, Plant Biology and Conservation, Northwestern University
Selected Professional Associations
My research interests are focused on the reproductive ecology and population demographics of rare and threatened plants.
I am particularly interested in how populations of rare and threatened plants fare under management schemes that are often targeted at community structure and ecosystem functioning, rather than on maintaining occurrences of any individual species. I work on several species of state and federally listed plant species (Cirsium pitcheri, Platanthera praeclara, Viola conspersa, Lespedeza leptostachya), attempting to elucidate the effects of management which include grazing, burning and invasive species removal.
Conservation research on rare species has also provided a framework within which to understand the biological consequences of small and fragmented populations. In this way, rare plants can serve as model species as we strive to understand how continued habitat fragmentation will affect more common species.
Sometimes, however, rare species don't lend themselves to experimental manipulation, and more common model species may be used to elucidate patterns of resource allocation and how demographic trade-offs may influence vital rates and population trajectories.
In addition, I am interested in elucidating the multiplicative impacts of climate change in the context of fragmented landscapes, and how species will respond to these challenges over time. For example, many species are contending with both rapid climate change and barriers to migration on top of other anthropogenic influences such as habitat conversion and pollution.
Arisaema triphyllum (Jack-in-the-Pulpit) — This gender-switching species, though common, serves as a model species to understand the effects of reproductive choices on population dynamics. Reproductive individuals in this species may be either male or female, depending upon size, with the largest plants expressing as female. Environmental conditions are known to effect the expression of gender and we completed a two-year study in 2011 looking at the effects of pollen load on the sex ratio of two populations in Lake County Illinois. This study also examined the effects of habitat management on gender choices and population sex ratio. Management for an open-canopy, particularly by removing invasive buckthorn, appears to increase the number of females in population. (Vitt and Tienes)
Cirsium pitcheri (Pitcher's thistle) — In 2011 we completed work on a five-year grant to study the demography and genetics of Cirsium pitcheri, a threatened species that occurs around Lake Michigan. We found that the species is in decline, all monitored populations are below replacement rate due to numerous threats including invasive species, predation by goldfinches and predation by a biocontrol weevil introduced to control weedy thistles. In 2011 we began demographic monitoring of the weevil-infested population in Wisconsin to track weevil effects (Havens-Young, Fant, Vitt and outside collaborators).
Lespedeza leptostachya (Prairie Bush Clover) — We have been monitoring populations of this Federally Threatened gravel-hill prairie species at Nachusa Grasslands in Franklin Grove, IL and Harlem Hills Nature Preserve, part of Rock Cut State Park in Rockford, IL, to determine best management practices since 2000. In 2011, we completed 4 years of an experimental demography study to elucidate the role of grass competition on vital rates, and have determined that reducing competition increase seedling recruitment, as does limited cattle grazing. In response, the stewards at Nachusa Grasslands are in the process of writing a management plant that will include bison. We will conduct an exclusion study at the time of bison introduction to determine the efficacy of this approach. (Vitt, Havens-Young and outside collaborators).
Viola conspersa — Using ten years of volunteer-collected data, we have created a regional model of the state-threatened Viola conspersa to determine the effects of habitat management on vital rates and population viability, particularly removal of invasive buckthorn canopy. Invasion by buckthorn forms a densely closed canopy that reduces reproduction via open-pollinated flowers in favor of production of closed-pollinated flowers. The shade created by a buckthorn canopy also affects survivorship and patterns of seed set, potentially causing local extinction. Using ten years of "before and after" data from six populations of Viola conspersa, which had undergone buckthorn canopy removal at various points throughout the decade, we created integral projection models to understand the effects of management. Because management affects the ratio of open- to closed-floral ratio, we were able to explicitly model the effects of management on patterns of genetic diversity as well as population growth rate in light of the frequency of habitat restoration activities. Results showed that more open-pollinated flowers were produced when buckthorn canopy was removed periodically (every few years), suggesting that restoration activities such as removal of invasive species is favorable both to population size and to maximizing genetic diversity. Such results show that management may result in populations with greater genetic diversity and therefore more resilience to more effectively respond to environmental changes, such as a warming climate.
Ex Situ Conservation
Seed banking both rare and common species is an important aspect of plant conservation. I curate the Dixon National Tallgrass Prairie Seed Bank at the Chicago Botanic Garden, which has a collection focus of native prairie species. We target the tallgrass prairie, because it is the most endangered ecosystem in North America, having lost approximately 96 percent of its former extent to habitat conversion. I am particularly interested in applying GIS tools to create effective seed collection strategies.
Species Range Shifts
Many plant species will experience significant range shift as climate change proceeds over the coming decades. I have been using Species Distribution Modeling approaches such as MaxEnt and BioClim to model potential shifts of rare species across the Midwest. I am currently working with my postdoc Shannon Still on a project which examines the impact of global climate change on the species distribution of rare plants in the Great Basin. With this work we are examining the current distributions of rare plants and then making projections as to how these distributions will change between now and the year 2080.
Havens, K., C. Jolls, J. Marik, P. Vitt, A, K. McEachern, and D. Kind. Effects of an introduced biocontrol weevil, Larinus planus, and other emerging threats on populations of the federally threatened Pitcher's thistle, Cirsium pitcheri, In review, Biological Conservation.
Havens, K., P. Vitt and S. Masi. Citizen Science on a Local Scale: The "Plants of Concern" Program Undertakes Rare Plant Monitoring. In review, Frontiers in Ecology and the Environment.
Schwartz, M.W.1, Hellmann, J.J.2, McLachlan, J.M.2, Sax D.F.3, Borevitz, J.O.4. Brennan, J.5 Camacho, A.E.6, Ceballos, G.7, Doremus, H.8, Early, R.3, Etterson, J.R.9, Gill, J.10, Gonzalez, P.11, Green, N12, Hannah, L.13 Jamieson, D.W.14, Javeline. D.2, Minteer, B.A.15, Odenbaugh, J.16, Polasky, S17., Richardson, D.M.18, Root, T.L.19, Safford, H.D.1,20, Sala, O.15, Schneider, S.H.21, Thompson, A.R.24, Williams, J.W.10, Vellend, M.23, Vitt, P.24, Zellmer, S.25. Integrating the scientific, regulatory and ethical challenges posed by managed relocation. In review, BioScience.
Knight, T.M., K. Havens and P. Vitt. 2011. Will the use of less fecund cultivars reduce the invasiveness of perennial plants? BioScience 61(10): 816-822.
Fant, J.B., A. Banai and P. Vitt. Morphological and molecular evidence of hybridization between the federally threatened Lespedeza leptostachya Englem. and its co-occurring congener Lespedeza capitata Michx. Conservation Genetics 11(6): 2195-2205.
Vitt, P., K. Havens, A.T. Kramer, D. Sollenberger, and E. Yates. 2010 Assisted Migration of Plants: Changes in Latitudes, Changes in Attitude. Biological Conservation 143 (1): 18-27.
Vitt, P. K. Havens and O. Hoegh-Guldberg. 2009. Assisted migration: part of an integrated conservation strategy. Trends in Ecology and Evolution 24: 473-474.
Vitt, P., T. Knight, and B.P. Kendall. 2009. Effects of Community Level Management on Agalinis auriculata, a Rare Non-Target Prairie Annual. Biological Conservation 142 (4): 798-805.
Vitt, P. and K. Havens. 2004. Integrating quantitative genetics into ex situ conservation practices. In: Saving the Pieces: The value, limits, and practice of off-site plant conservation, E.O. Guerrant, K. Havens, M. Maunder (eds).
Vitt, P., K.E. Holsinger, and C.S. Jones, 2003. Local differentiation and phenotypic plasticity of size and gender change in Arisaema triphyllum. Am. J. Bot.
Vitt, P. 2001. Gender-related and genotypic differences in gas exchange of male and female clones of the gender-switching species Arisaema triphyllum (Araceae). Rhodora. 103: 387-404.
Vitt, P. and C.S. Campbell, 1997. The Reproductive Biology of Isotria medeoloides (Pursh) Raf. Orchidaceae. Rhodora.
Holsinger, K.E. and P. Vitt, 1996. The future of conservation biology: what's a geneticist to do? in Enhancing the Ecological Basis of Conservation: Heterogeneity, Ecosystem Function and Biodiversity. Proceedings from the Carey Conference VI, 1995.
Alona Banai (Master’s degree completed)
Rachel Olson (Master’s degree completed)
Melissa Tienes (Master’s degree student)