Document: ALA-3-37-5

The role of interspecific competition in the distribution of Aeschynomene virginica (Fabaceae).

GRIFFITH, A.B.* and I.N.FORSETH

University of Maryland, College Park, MD 20742 USA ¹

Abstract:
Aeschynomene virginica (Fabaceae) is an annual, wetland plant often found on accreting sandbars and muskrat "eatout" areas. We hypothesized that competition plays a key role in the distribution of this threatened plant. A replicate, block design showed significant differences in several demographic parameters. Seeds were sown in plots with naturally occurring vegetation removed or left standing. Individual plants were monitored monthly for germination, survivorship, growth, and reproduction. In 1998, mean germination was 21.6% versus 8.7% in low and high competition plots, respectively. Germination rates were 46.7% versus 26.3% in 1999. Mean survivorship to reproduction was 17.4% versus 3.9% in 1998 and 25.3% versus 0.3% in 1999. Mean seed set per plant was 111.5 versus 31.1 in 1998 and 155.0 versus 1.6 in 1999. Competition placed multiple pressures on A. virginica populations. While establishment probability varied between years, fewer seeds established under competitive pressure both years. Even after successful establishment, fewer seedlings survived to reproduce. Finally, plants growing under competitive conditions were smaller and produced less seeds. Thus, several stages of this plant's life cycle contributed to greater population growth under a low competition environment. These results strongly suggest the distribution of A. virginica may be linked to disturbance regimes in its marsh habitat, like muskrat activity and newly deposited sediments.

Keywords: competition; distribution; rare plant; threatened plant; demography; wetland

This abstract is being presented at: 10:30 AM in session:
PLANT DEMOGRAPHY