AN EXPERIMENTAL-STUDY OF THE ROLE OF SEEDLING DENSITY AND NEIGHBOR RELATEDNESS IN THE PERSISTENCE OF RUMEX-ACETOSELLA IN AN OLD-FIELD SUCCESSION

Patterns in flowering and biomass allocation in seedlings of Rumex ace tosella L. collected from five successional old fields, from 1 year ol d to 15 years old, have been examined in experimental pots varying in density (1, 2, and 4 plants/pot) and neighbor relatedness (sib, nonsib , other population) to determine the effects of successional habitat v ariation on patterns of resource allocation. The flowering of seedling s from the successionally young populations was not affected by densit y, whereas for seedlings from the older populations, increased density was correlated with increased variation in flower and seed production both within and between populations. At high density, seedlings from the successionally youngest population showed the greatest allocation of resources to flowering. As a result, differentiation along the succ essional gradient was such that the younger populations invested a gre ater proportion of resources to aerial biomass, while the older popula tions allocated relatively more resources to vegetative propagation. T hese trends were maintained at high density. The results of the siblin g competition treatment showed no consistent trend related to the age of the populations but were density dependent. At high density, sexual biomass was higher between nonsibs than between sibs of the same popu lation, suggesting greater competition among related plants. Finally, the sexual biomass of individual plants was less in competition with s eedlings from a different population than with seedlings from the same population. Sprout biomass showed the reverse trend. The observed dif ferentiation between successionally different populations in resource allocation irrespective of density may account for these results. Over all, our results provide evidence for biotic specialization of R. acet osella in relation to successional habitat change.