R. Tucker Gilman

Tucker Gilman

Contact Information:
Institute for Mathematical and Biological Synthesis (NIMBioS)
Blount Hall
1534 White Ave., Suite 400
University of Tennessee
Knoxville, TN 37996-1527
Phone: (865) 974-4892
Fax: (865) 974-9300
email: rtgilman@nimbios.org

Research Interests:
It has traditionally been assumed that ecology and evolution operate on different time scales, and that ecological systems can be adequately understood when the character of species is assumed to be constant.  However, a growing body of research suggests that evolution can interact directly with population dynamics on a time scale that has often been considered ecological, and so may play an important role in structuring and maintaining ecological communities.  My fundamental research interest is in understanding how species evolve in response to changes in their environments, including evolutionary changes in the species with which they interact, and in understanding how such evolution can affect community structure.  I have used mathematical models to focus on three distinct questions: 

How will evolution affect the persistence of mutualisms in a changing environment?
Climate change is altering the phenologies of both plants and animals.  There is growing evidence from the field that climate-induced phenological change can desynchronize the activity periods of interdependent species, with potentially catastrophic effects on populations.  Evolution can allow populations to persist though climate change events when they would otherwise be extirpated.  I have used mathematical models to investigate the conditions that make the evolution of mutualist species in a changing environment more or less likely.  Mutualisms may be more likely to survive climate change when one or both species have alternative mutualist partners.  However, if alternative partners are abundant, focal mutualists may be less likely to evolve together and the focal mutualism may be more likely to be disrupted.  In collaboration with colleagues I am currently developing a framework to expand these results to more complex ecological communities.

Gilman. R. T., N. S. Fabina, K. C. Abbott, and N. E. Rafferty. 2011. Evolution of plant-pollinator mutualisms in response to climate change.  Evolutionary Applications. Published [Online] Sept. 7, 2011.
Fabina, N. S., K. C. Abbott, and R. T. Gilman. 2010. Sensitivity of plant-pollinator-herbivore communities to changes in phenology.  Ecological Modelling 221(3):453-458. [Online]

How do processes of adaptive divergence respond to environmental change?
There are now a number of well-documented cases in which hybridization between incipient species has increased, sometimes resulting in the replacement of parental populations by a hybrid swarm.  Several potential explanations for these events have been proposed, including resource homogenization, reduced signal transduction, and increased cost of choosiness in mating.  I have used individual-based models to simulate the effect of these disturbances on incipient species pairs.  While each mechanism is capable of disrupting speciation, the species collapse process and the expected phenotypes of the hybrid population after collapse are different in each case.  Moreover, in some cases incipient species may be able to rapidly re-evolve, while in other cases the collapse is likely to be permanent.

In addition to the effects of environmental change on incipient species, I am interested in the more fundamental question of how and when reproductive isolation can evolve in a panmictic population.  I am currently working with colleagues to investigate cases in which reproductive isolation and adaptive divergence through sexual dimorphism might evolve concurrently or sequentially in sympatry.

Gilman, R. T. and J. E. Behm. 2011. The collapse of speciation processes in response to environmental change.  Evolution 65(9):2592-2605. [Online]
Cooper, I. A., R. T. Gilman and J. W. Boughman. 2011. Sexual dimorphism and speciation on two different ecological coins: patterns from nature and theoretical predictions. Evolution 65(9):2553-2571.[Online]

How does environmental variability affect the evolution of dispersal?
When habitat quality varies in space but not in time, theory suggests that dispersing phenotypes should not evolve.  In nature habitat quality does vary in time, and one of the most important sources of variation is seasonality.  I have used mathematical models to investigate the conditions under which evolution can lead to dispersal from a permanent range to a seasonal range.  For species with short generation times, selection can favor multiple dispersing phenotypes with distinct mean dispersal distances.  As the number of generations achieved in the seasonal range in each year increases, the mean dispersal rate in the population increases as well.  Many crop pests in the northern United States and Canada are seasonal residents with overwintering ranges limited to the southern United States, Mexico, and the Caribbean region.  If climate change increases the length of the “summer” season, my results suggest that dispersal rates and distances of some insects may increase.  This may affect the range and density of some economically important insect pests.

Other interests:
In addition to evolutionary theory, I am also interested in the statistical analysis of ecological data.  In one example, I have worked with movement and mortality data on an urban white-tailed deer population undergoing management with female sterilization.  The data set was challenging because range size estimators are known to be biased and because only a small number of highly non-random mortalities were recorded.  Using a combination of parametric and non-parametric approaches, I was able to show that sterilization increases the home range size of does, and that mortality rate is positively correlated with home range size.  This result has implications for management of overabundant urban and suburban deer populations.

Gilman, R. T., Skinner, B. G., Frank, E. S., Julis, V. B., Paul-Murphy, J., and Mathews, N. E. 2010. Effects of Maternal Status on the Movement and Mortality of Sterilized White-tailed Deer Does.  Journal of Wildlife Management 74(7):1484-1491. [Online]