Associate Professor of Biology
Office: Reem-Kayden Center 211
Home Page: http://biology.bard.edu/faculty/keesing/
Ph.D., Integrative Biology (1997), University
of California, Berkeley
B.S., Symbolic Systems (1987), Stanford University
Biodiversity, Ecology, Ecology of African Savannas I and II, Sex and Gender
Research on African Savannas
My scientific research focuses on networks of interactions among species, and particularly on the consequences of these interactions for ecological communities. I currently have two primary research projects. The first is on how the loss of large mammals in Kenya influences savanna community dynamics, and the second is on how biodiversity influences Lyme disease risk in the eastern U.S.
My project in Kenya began in 1995 and took advantage of an experiment that was being set up at that time to exclude different combinations of large mammals from savanna habitat. My dissertation research focused on how the exclusion of large mammals in this system influenced small mammal diversity and abundance, and how small mammals in turn influenced vegetation. I found that when large mammals were absent, small mammal populations exploded in abundance, and that these high densities of small mammals were capable of keeping the vegetation at levels similar to those when large mammals were present. This compensatory herbivory by small mammals had not been documented before, and was particularly surprising in African savannas where the large, charismatic mammals like zebras and wildebeests were considered to be by far the most important herbivores. These results have conservation implications because large mammals are disappearing from vast areas of Africa, which may cause compensatory responses by herbivorous rodents. A savanna over-run with rodents rather than herds of antelopes would likely have a higher incidence of diseases (for which rodents are often reservoirs) and a predator community dominated by poisonous snakes such as puff adders and cobras. Preserving large mammals in Africa, therefore, may be a critically important means of protecting human health in savannas.
In the last several years, my Kenya project has expanded to include a suite of other effects of the removal of large mammals. For example, my graduate student, Darcy Misurelli, has found that songbird diversity is particularly high when elephants and giraffes are excluded. Together with students and my colleague, Rick Ostfeld, I am investigating how tick populations respond to the loss of large mammals. I am also studying how the plant community is influenced by the large-mammal removal treatments. Margey Shaw ('01), Ostfeld, and I completed a study that suggests that when large mammals are absent, mortality of tree seedlings actually increases as a result of an indirect interaction between invertebrates and large mammals. Jacob Goheen, a Ph.D. student, recently conducted a large-scale study of this effect that was published in Ecology.
This work is currently supported by a five-year $500,000 CAREER grant from the National Science Foundation. This grant also provides funding for me to take seven students to Kenya for each of four years so that these students can conduct research on savanna ecology under my supervision. To date, 20 Bard students have completed projects in this program.
Research on Disease Ecology
My second primary research program is based at the Institute of Ecosystem Studies in Millbrook, NY. Together with my colleague, Rick Ostfeld, I am investigating how the risk for humans of contracting Lyme disease is influenced by interactions among forest vertebrates, the causative agent of Lyme disease, and its vector, the blacklegged tick (Ixodes scapularis). Lyme disease is caused by a bacterium (Borrelia burgdorferi) which is passed between hosts through the bite of an infected tick. Hosts vary in their ability to infect ticks, or their reservoir competence. For example, white-footed mice (Peromyscus leucopus) transmit the Lyme bacterium to 90% of ticks that feed on them; they have extremely high reservoir competence. On the other hand, very few ticks that feed on deer (Odocoileus virginianus) pick up the infection, even if the deer are infected. Ostfeld and I have developed a conceptual model called the dilution effect, which suggests that when the diversity of hosts for ticks is high, Lyme disease risk is low, because the presence of a rich assemblage of hosts dilutes the impact of the high reservoir competence of white-footed mice. Together with a summer undergraduate research student, Brian Allan, we have demonstrated that the fragmentation of forest into small patches causes a dramatic increase in Lyme disease risk because non-mouse hosts disappear from small areas of forest, a study that appeared in Conservation Biology. Together, these results demonstrate that biodiversity and the preservation of intact forests can protect human health.
My research on Lyme disease is supported by grants from the National Institutes of Health, with Ostfeld and several other collaborators, including Ken Schmidt (Texas Tech University) and Kathleen LoGiudice (Union College).
As part of my NSF grant for the Kenya research, I am also conducting educational research on student learning. Students who participate in my "African Savannas" program are simultaneously subjects in a project to understand how the conduct of research influences their understanding of the nature of knowledge.
I am also a co-director of the Research Experiences for Undergraduates (REU) program at the Institute of Ecosystem Studies in Millbrook. This program, which has been running since the inception of the REU program by NSF, is characterized by its emphasis on the social contexts in which ecological research takes place. In addition to conducting their own individual projects, students in this program conduct a group investigation into an ecological issue with societal implications (e.g. PCBs in the Hudson River, control of West Nile Fever virus), develop an ecology experience for underprivileged kids, explore alternative careers in ecology through a day-long career forum, and have regular workshops and roundtables on other issues. I have mentored students in this program each summer for a number of years, and I assist in the oversight, assessment, and development of the program itself
- Keesing, F. 1998. Impacts of ungulates on the demography and diversity of small mammals in central Kenya. Oecologia 116:381-389.
- Keesing, F. 2000. Cryptic consumers and the ecology of an African savanna. BioScience 50:205-215.
- Ostfeld, R.S. and F. Keesing. 2000. Biodiversity and disease risk: the case of Lyme disease. Conservation Biology 14(3): 1-7.
- Ostfeld, R.S. and F. Keesing. 2000. Pulsed resources and community dynamics of consumers in terrestrial ecosystems. Trends in Ecology and Evolution 15: 232-237.
- Ostfeld, R.S. and F. Keesing. 2000. The function of biodiversity in the ecology of vector-borne zoonotic diseases. Canadian Journal of Zoology 78:2061-2078.
- *Shaw, M.T., F. Keesing, and R.S. Ostfeld. 2002. Patterns of predation on Acacia seedlings in an African savanna. Oikos 98(3): 385-392.
- *Allan, B.F., F. Keesing, and R.S. Ostfeld. 2003. The effect of habitat fragmentation on Lyme disease risk. Conservation Biology 17:267-272.
- LoGiudice, K., R.S. Ostfeld, K. Schmidt, and F. Keesing. 2003. The ecology of infectious disease: Effects of host diversity and community composition on Lyme disease risk. Proceedings of the National Academy of Sciences 100: 567-571.
- *Shaw, M.T., F. Keesing, R. McGrail, and R.S. Ostfeld. 2003. Factors influencing the distribution of larbal blacklegged ticks on rodent hosts. American Journal of Tropical Medicine and Hygiene 68:447-452.
- Ewing, H., K. Hogan, F. Keesing, H. Bugmann, A. Berkowitz, L. Gross, J. Oris, and J. Wright. 2003. The role of modeling in undergraduate education. Pages 413-427 in: C.D. Canham and J. Cole, eds., Models in Ecosystem Science. Princeton University Press.
- Goheen, J., F. Keesing (corresponding author), B. Allan, D. Ogada, and R.S. Ostfeld. 2004. Net effects of large-mammal exclusion on Acacia seedling survival in an East African savanna. Ecology 85:1555-1561.
- Ostfeld, R.S., P. Roy*, W. Haumaier, L. Canter, F. Keesing, and E. Rowton. 2004. Sandfly (Lutzomyia vexator) populations in upstate New York: abundance, microhabitat, and phenology. Journal of Medical Entomology 41(4): 774-778.
- Ostfeld, R.S. and F. Keesing. 2004. Oh the locusts sang, then they died. Science 306:1488-1489. [Perspective]
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