Seed dispersal mutualism and the population density of Asarum canadense, an ant-dispersed plant

Abstract

The dispersal of seeds from Asarum canadense by ants was studied to quantify variation in mutualistic benefits and to test the hypothesis that this mutualism has effects on population density. Six populations of A. canadense were monitored in SE West Virginia, in the Monongahela National Forest. The rate of seed removal, dispersal distance, microhabitats of dispersed seeds and disperser species were determined in each study site. I measured ovule production and factors causing loss of ovules and the seeds resulting from them through the stage of dispersed seeds. The proportion of seeds removed from the area under the parent plant was the best indicator of dispersal benefits. Few components of dispersal varied among the six sites, but significant variation was observed for capsule formation, ovule development, and pre-dispersal seed predation. Key factor analysis showed pre-dispersal seed predation to be the major factor influencing spatial variation in seed production. Seedling density in 1984 was directly related to seed production in 1983. No population feedback for mutualism was detected.