POPULATION AND GENOTYPE NICHE WIDTH IN CLONAL PHLOX PANICULATA

We use a model population comprised of five genotypes of Phlox paniculata L. to investigate the contribution of individuals to the response breadth (niche) of the population on a light gradient and a moisture gradient. Analysis of within- and between-genotype components of population response width showed up to 20% of the response is due to between-genotype effects, depending upon the character considered. Since the only way a sedentary organism can deal with a variable environment is through plasticity of response, differences in levels of phenotypic plasticity between genotypes on the two resource gradients were also investigated. There was no correlation between level of phenotypic plasticity and success over a range of environments. Niche breadth calculated as Levins' (B) and Roughgarden's (w²) indicated that flowering, and hence sexual reproduction, was limited to a much narrower range of environments than was vegetative growth. We also found significant genotype × environment interactions on both gradients, indicating differences in genetic response to the environment.