PARENT SESSION
Oral Session # 34: Plant Ecology II: Pollination and Dispersal.
Presiding: A McEuen
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 202.

Can one plant species rescue another from low-density effects on pollinator visitation and fruit set?

Feldman, Tracy ^*,1, ¹ Biology Department, Duke University, Durham, NC, USA

ABSTRACT- Plants occurring at low densities may receive fewer visits by pollinators, and may produce fewer seeds than plants occurring at higher densities. These low density effects may be altered by co-flowering plants if these plants increase or decrease attractiveness of a focal species to pollinators. Even if pollinator visits increase, reproductive success of focal plants could either decrease or increase if co-occurring plants compete for or facilitate pollination, respectively. I conducted a large scale spatial experiment to test whether one plant species can rescue another from low-density effects on pollinator visitation and fruit set, using the common perennial plant Piriqueta caroliniana as a focal species, and Coreopsis leavenworthii as a co-flowering species. I set up eight artificial arrays of 10 P. caroliniana plants each, at four different densities, either alone or evenly interspersed with the co-flowering species. On each of five days, I recorded all pollinator visits to each patch in 15-minute observation periods, and visitation sequences of all pollinators within each patch. After each of five temporal replicates, I counted the number of fruits on each P. caroliniana plant. I used these data to calculate visitation rate to patches, visitation rate to individual plants, and percent fruit set, and conducted Analyses of Deviance to test for effects of density and co-flowering species on these variables. The visitation rate of pollinators to patches, the visitation rate of pollinators to plants within patches, and fruit set all increased with increasing plant density. However, I detected no effect of the co-flowering species, perhaps due to lower than predicted overlap among pollinator species, or to high pollinator constancy. Low density effects may have serious consequences for populations (e.g., Allee effects) if plants at low densities do not produce enough seeds to replace dying individuals.

Key words: pollinator visitation, low density effects, facilitation for pollination