Population dynamic consequences of habitat heterogeneity: an experimental study

Rainfall fluctuations affect the dynamics of the desert annual Stipa capensis population studied in the Jordan Rift Valley by influencing both the percentage of germination and the number of seeds produced per germinated plant. However, the effect of changes in rainfall on both demographic parameters depends on habitat conditions, with slope subpopulations exhibiting the largest, and wadi subpopulations the smallest, effects. Subpopulations inhabiting different habitats show considerable differences in their year-to-year fluctuations in density. Since seed production per seedling is habitat dependent, the distribution of the seedling population among the various habitats is a major determinant of the total number of seeds produced by the population in a given year. Most of the seeds (75-99.9%, depending on rainfall conditions) are produced in the depressions and the wadis, which taken together account for only 10% of total area. -from Author