Density-Dependence in Salvia Lyrata: Experimental Alteration of Densities of Established Plants

Abstract

(1) Two experiments were conducted in a natural population of Salvia lyrata to investigate the effects of conspecific density on survival, fecundity and growth of established individuals. In both experiments, the density around monitored Salvia individuals was altered, either by removal of surrounding Salvia individuals within a specified distance, or by planting Salvia in as neighbours. (2) In both experiments, survival, fecundity and growth showed small responses to the density manipulations. The responses varied with individual size. In large individuals these traits tended to decrease with increasing density, whereas small plants were in several respects favoured by more crowded conditions. (3) The weakness of the responses to neighbours suggests that the population of mature Salvia is not strongly self-regulating at typical natural densities or that marked effects of crowding appear only after a delay of more than two years. Mortality at the seedling stage as well as density-independent determinants of growth appear to maintain the adult population below the threshold at which neighbour interactions have strong effects.