Density-dependent population regulation in a Texas grassland

This study examines the extent to which plant population dynamics are affected by density—dependent processes, and at what stage(s) in the life cycle density—dependent effects occur. A natural population of Bouteloua rigidiseta, a perennial grass, was subjected to two changes of density, the addition of seeds and the removal of 30—40% of the adult plants. Censuses were conducted before and after these treatments, one year apart. Survival, growth, and reproduction were all highly size dependent. Seed additions increased proportionately the number of new recruits to the population, indicating that the size of this age class was limited by seed input; seed additions decreased the size of new recruits. Adult removal tended to increase the sizes of both new recruits and adults. Thus competition among adults, among recruits, and by adults against recruits, but not competition by recruits against adults, affected this population in a density—dependent fashion. No density—dependent treatment effects involving rep...