ESS germination strategies in randomly varying environments. II. Reciprocal Yield-Law models

Abstract

The study of ESS germination fractions in S. Ellner (1985, Theor. Pop. Biol. 27, 000-000) is applied and extended in the case of annuals obeying the Reciprocal Yield Law. The effects of parameter changes on the value of the ESS germination fraction are determined in some limiting cases by analyses of approximations. Numerical solutions of the ESS criterion are used to check the robustness of the conclusions and the accuracy of the approximations. In general, the ESS germination fraction decreases with an increased survivorship of buried seeds and with increased "variability" of seed yields. However, different measures of "variability" are appropriate in different circumstances. To avoid the possibility of conflicting predictions depending on the measure of variability, it is suggested that tests of the theory be limited to co-occurring species, and to variability due to climatic fluctuations. The ESS theory based on the Reciprocal Yield Law is compared with D. Cohen's (1966, J. Theor. Biol. 12, 119-129; 1968, J. Ecol. 56, 219-228) density-independent theory of "optimal" germination. The theories differ qualitatively and quantitatively regarding the influence of mean yield, seed survivorship, and the frequency of favorable years on the predicted germination fraction.