PARENT SESSION
Oral Session # 32: Herbivory II: Grasslands.
Presiding: K Suttle
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 200.
Direct and indirect effects of extreme drought on compensation following herbivory in Ipomopsis aggregata (Polemoniaceae).
Levine, Mia*,1, Paige, Ken1, 1 University of Illinois at Urbana-Champaign, Urbana, IL
ABSTRACT- Compensation following herbivory is now appreciated as an important element of plant defense; however, variation in compensation under naturally stressful conditions has yet to be evaluated directly. During Arizona's worst drought on record, a typically overcompensating population of Ipomopsis aggregata severely undercompensated through female function. We tested two factors that potentially contributed to this atypical pattern of undercompensation: 1) The direct effect of extreme water stress on the capacity to compensate (following the typical single bout of herbivory) and 2) The indirect effect of water-stress on compensation through drought-associated ungulate browsing. We assessed the direct effect of water stress using a 2 x 2 fully factorial experiment with treatments: +/- supplemental water, +/- clip (simulating the typical single bout of herbivory). We found a significant clip x water interaction for female fitness, suggesting that water limits compensation through female function. Simulated herbivory had a larger detrimental effect on female fitness in the nonwatered plants than on the watered treatment plants. Moreover, watered plants equally compensated (similar seed production in unclipped and clipped treatments) while water-stressed plants undercompensated (fewer seeds in clipped treatment) through female function. In the second experiment, we examined the indirect effect of drought on compensation through ungulate browsing by comparing 1) unbrowsed plants (caged), 2) clipped plants (simulating typical single bout of herbivory, caged), and 3) unprotected natural controls (open to natural browsing levels). The natural controls suffered unprecedented levels of herbivory, resulting in severe undercompensation. We conclude that although water was an important limiting factor for compensation during the drought year, the overriding factor determining fitness achieved through compensation was the indirect effect of drought-- drought-associated ungulate browsing. Implications for plant-animal interactions under future climate change are discussed.
Key words: compensation, drought, ungulate herbivory, Ipomopsis aggregata