PHENOTYPIC PLASTICITY AS RELATED TO TRAMPLING WITHIN A NATURAL-POPULATION OF POLYGONUM-AVICULARE SUBSP-AEQUALE

Phenotypic and genotypic differentiation was investigated in a natural population of the annual weed Polygonum aviculare subsp. aequale experiencing heterogeneous trampling intensity. Sixteen morphological and life history characters were studied. Cultivation in untrampled conditions suggested that the differentiation observed in the field could be entirely accounted for by phenotypic plasticity. A principal component analysis revealed that shoot length and all the variables describing metamer components were highly positively correlated with each other. Moreover, they showed a similar plastic response, i.e. a marked decrease in relation to trampling intensity. In contrast, biomass allocation to reproduction showed a positive response to trampling, while the total number of metamers and total weight showed no significant response to trampling. It is suggested that the norms of reaction observed in the field are of adaptive value.