Seed fate in an ant-dispersed sedge, Carex pilulifera L.: recruitment and seedling survival in tests of models for spatial dispersion.

The spatial pattern of recruitment and seedling survival was studied in an ant-dispersed sedge (Carex pilulifera L.) in a forest clearing in Denmark. Seedlings were generally more aggregated than juvenile and adult plants. Recruitment distances were skewed towards larger values. While 72% plants of presumably ant-dispersed origin survived for 5 years, only 13% auto-dispersed plants were still alive, predominantly as persistent seedlings. The survivorship showed a negative exponential decrease (Deevey type II) with an expected half-life of 17 months for auto-, and 10 years for ant-dispersed plants. Growth-rate and fecundity were significantly larger for ant-dispersed plants than for auto-dispersed plants. Computer simulation was used to test three different dispersal models and two mortality types on the recruitment pattern observed in the field. The simulations confirmed the importance of ant dispersal for recruitment, but gave no conclusive evidence for evaluating recruitment from ant-nests. High mortality levels, comparable to observed predation levels, were needed to simulate field conditions. Density-dependent mortality proved more powerful than distance-dependent mortality in the simulations. Results are discussed in the context of current hypotheses of seed dispersal. While the directed dispersal hypothesis could not be rejected, results were generally more favourable to the escape hypothesis.