PARENT SESSION
Oral Session #19: Plant Competition. Presiding: N. Slade.
Monday, August 6, 2001. 1:00 PM to 5:15 PM. Hall of Ideas J.
The role of intraspecific competition in size and fecundity variation in Draba verna L.
Mulroy, Juliana1, Emery, Sarah2, 1 2
ABSTRACT- Draba verna L. (Erophila verna CAM) is a small winter annual plant of particular ecological interest. A seven-year study in Poland demonstrated strong effects of density on plant size, including overcompensating density dependence in a two-year cycle. An Allee effect on fecundity unrelated to pollination vector has been suggested in a North American population. The Polish study did not track the fate of individual plants, but instead measured average local density from year to year; the North American study looked at density at time of reproduction only. Earlier we suggested that the reported overcompensation might be an artifact of scale and/or due to genetic similarity (inferred from classic genetic studies, hybrid crosses, and phenotypic similarity) of competing individuals. Individuals from 20 North American sites, including several in the area of our study, now have been determined to be genetically indistinguishable within sites using ISSR markers. To measure intraspecific competition, we established common garden populations with a homogeneous substrate and seeds from a single site, and tracked individual growth over time in relation to neighbors using repeated photography and image analysis. Size and distance of neighbors early in the life cycle account for more variation in final size and fecundity than do size and distance of neighbors at or near reproduction, yet 70% of variation in final size and fecundity variation remains unexplained. We now are investigating whether maternal effects play a significant role in the outcomes reported in previous studies.
KEY WORDS: Draba verna, Erophila verna, intraspecific competition, image analysis, maternal effects