REPRODUCTIVE HIERARCHIES IN ERODIUM - EFFECTS OF VARIATION IN PLANT-DENSITY AND RAINFALL DISTRIBUTION

In populations of Erodium botrys and E. brachycarpum, reproductive inequality within monocultures of both species increased with increasing plant density and plant productivity. Plant productivity (measured by seed production) was determined by rainfall distribution. The magnitude of reproductive inequality was dependent on the interaction of sowing density and rainfall distribution. At the highest sowing density, reproductive inequality was greatest in populations that experienced early autumn precipitation and lowest in populations exposed to drought during flowering. At the lowest sowing density there was no significant effect of rainfall pattern on reproductive inequality. Effective population number was relatively insensitive to increases in population density because of increased inequality in reproduction at higher population densities. Reproductive variance could be a major contributor to drift variance in dense populations. -from Author