PARENT SESSION
Oral Session # 65: Herbivory V: Deer, Geese, and Chemistry.
Presiding: K Bjorndal
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 103.

Can evolution by natural selection rescue declining Trillium grandiflorum populations?

Knight, Tiffany^*,1, Holt, Robert¹, Barfield, Michael¹, ¹ University of Florida, Gainesville, FL, USA

ABSTRACT- Rapid changes to the environment create novel selective pressures for species, which could cause them to decline towards extinction, unless they rapidly evolve to a new phenotype. Although demographic analyses are often used to project the rate of decline for many species of concern, these analyses have not heretofore incorporated the potential for natural selection to alter those projections. Here, we estimated the degree to which natural selection on flowering time can rescue declining populations of the native wildflower, Trillium grandiflorum, that are experiencing novel levels of herbivory by white-tailed deer. We found that individuals flowering early in the season were much more susceptible to deer herbivory than those flowering later, and thus flowering time may be a trait that both would be under strong selection and could alter the rates of decline of this species. We employed two approaches to examine whether or not evolution of flowering time might rescue these declining populations from extinction. First, we coupled demographic and selection analyses (elasticities and mean standardized selection gradients) to project change in the population growth rate as mean flowering time changes. Second, we used individual-based simulations to determine the probabilities of adaptation and extinction, assuming flowering time is a heritable, quantitative trait. We compared the predictions of these two modeling approaches and relate these results to natural Trillium grandiflorum populations at risk of extinction.

Key words: demography, flowering time, herbivory, white tailed deer