Document: FRA-3-42-4

Trade-offs between plant growth and defense: A test using big sagebrush.

MESSINA, F.J.* ¹, J.H.RICHARDS ² and E.D.MCARTHUR ³

Utah State University, Logan, UT 84322 USA ¹
University of California, Davis, CA 95616 USA ²
USDA Forest Service, Provo, UT 84606 USA ³

Abstract:
We used intraspecific variation in big sagebrush, Artemisia tridentata, to examine the proposed trade-off between plant growth and defense. Seeds were obtained from seven geographic populations (including three subspecies) and an artificial hybrid, and 1,120 seedlings were established in a common garden. Plants in one set of plots were either unmanipulated, sprayed with insecticide, or clipped in a way that simulated moderate or severe browsing by ungulates. A second set of plots was used to measure ambient growth and reproduction, as well as natural colonization by herbivorous insects. Plant growth varied considerably among ecotypes; we observed two-fold variation in mean relative growth rates and more than seven-fold variation in mean aboveground mass after the first growing season. All ecotypes showed compensatory growth (but not overcompensation) in response to clipping. Contrary to prediction, the degree of compensation was unrelated to growth rate in the absence of herbivory. There was also no consistent relationship between plant growth and patterns of insect colonization, which were highly species-specific. At the level of geographic populations, we found little evidence of a built-in trade-off between inherent growth rate and the ability to tolerate or resist herbivory.

Keywords: plant defense, herbivory, relative growth rate, sagebrush, compensatory growth

This abstract is being presented at: 4:45 PM in session:
Oral Session #48: Anti-Predator Responses: Fish to Sagebrush.