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

Pollen limitation by pollinator and mate scarcity in fragmented Echinacea populations: individual- and population-based spatial perspectives.

Wagenius, Stuart^*,1, Pimm, Stephanie¹, ¹ Institute for Plant Conservation, Chicago Botanic Garden, Glencoe, IL

ABSTRACT- Reproductive failure due to pollen limitation is a consistent consequence of isolation for Echinacea angustifolia plants growing in a fragmented prairie landscape. Using this common, self-incompatible purple coneflower, we conducted two experiments to examine the contributions of pollinator visitation and mate availability to pollen limitation. In each experiment, we characterized the spatial pattern of nearby flowering conspecifics at a population scale (population size) and at individual scales (distance to the nth nearest neighbor for n = 1 - 8). In the study area in western Minnesota, USA, population sizes ranged from 2 to 4500, and distance to the first nearest neighbor ranged from 0.1 m to 127 m. In the first experiment, we focused on sixteen remnant populations. In each population, we determined compatibility between six focal plants and each of their six-closest flowering neighbors. We found that mean compatibility between pairs of plants increased with population size over the range of sizes found in our study area. Preliminary results showed a relationship between isolation of individual Echinacea plants and compatibility at some spatial scales. In the second experiment, we observed and collected insect visitors of 254 flowering Echinacea plants in 20 prairie remnants. We visited each site 3-4 times during the flowering season, and observed 5 randomly selected plants during each visit. Echinacea appears to be pollinated primarily by native bees, with 8 genera of bees from 4 different families (Halicitidae, Anthophoridae, Andrenidae, Megachilidae) represented. We were unable to detect any clear relationship between the frequency of bee visitation and Echinacea population size, or between the frequency of bee visitation and the isolation of individual Echinacea plants. We discuss the roles of pollinator scarcity and mate availability as factors limiting the reproduction of Echinacea in fragmented landscapes by comparing the spatial patterns observed with both individual- and population-based perspectives.

Key words: habitat fragmentation, pollen limitation, bees, self-incompatibility