PARENT SESSION
Contributed Oral Session 85: Mutualism: Pollination
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 520 C, Level 5, Palais des congrès de Montréal
Causal models of pollination in a montane herb: Scale matters!.
Waser, Nickolas*,1, 2, 6, Price, Mary 1, 2, 6, Irwin, Rebecca1, 3, Campbell, Diane1, 4, Brody, Alison1, 5, 1 Rocky Mountain Biological Laboratory, Crested Butte, CO, USA2 University of California, Riverside, CA, USA6 School of Natural Resources, Tucson, AZ, USA3 Dartmouth College, Hanover, NH, USA4 University of California, Irvine, CA, USA5 University of Vermont, Burlington, VT, USA
ABSTRACT- Most angiosperms depend on animal visitors for pollination, but variation in pollinator services to individual species is poorly understood. We censused pollinators and floral "larcenists" visiting the semelparous montane herb Ipomopsis aggregata over seven summers at permanent study sites separated by several hundred m, and counted pollen delivered to flowers on a subset of plants observed for visitation. Species composition of the visitor community varied significantly across years and within the flowering season, sites did not vary except except in the magnitude of parallel annual changes in their visitor communities. Total rates of flower visitation fluctuated over an order of magnitude or more. Variation in mean stigma pollen load among plants flowering in a given site and year was explained by a causal path model in which visitation rates by pollinators and larcenists had linear positive and negative effects, respectively. However, qualitatively different parameter estimates were produced by an analogous causal model based on population means across site-year combinations. This discrepancy of results from within- and between-population levels of analysis suggests that pollen receipt is influenced by environmental factors that vary among sites and years, in addition to variable pollinator visitation. We propose a heuristic causal model that includes such factors, and note some implications for ecological and evolutionary studies of pollination.
Key words: pollination, Ipomopsis aggregata, long-term study, temporal-spatial variation