VARIATION AND COVARIATION AMONG LIFE-HISTORY TRAITS IN RUMEX-ACETOSELLA FROM A SUCCESSIONAL OLD-FIELD GRADIENT

In this study morphological variation and the potential for competitio n to affect biomass and seedling selection of the families of five pop ulations of Rumex acetosella L. sampled along a successional old-field gradient have been investigated. Seeds from 25 families were submitte d to four competitive regimes: no competition (one plant per pot), med ium competition (two plants/pot taking plants from the same population ), high within-population competition (four individuals from the same population in a pot) and high between-population competition (four ind ividuals from two different populations in a pot). Eight traits were a nalysed after 3 months of growth for variation among families within p opulations. A significant difference among families within the two old er populations was recorded for sexual biomass and related components. High sensitivity of these traits to density was observed in all popul ations except the youngest, suggesting specialization to particular en vironmental conditions in late successional populations, and a good ad aptive capacity to buffer environmental variation in the pioneer popul ation. Little significant interaction between competitive regimes and families within populations was found, i.e. genotypes within each popu lation showed little variation in their response to environmental vari ation, Genotypic variance decreased with increasing competitive condit ions for the majority of the traits. However, the percentage of varian ce in sexual reproduction explained by family was stable among treatme nts. Tradeoffs between vegetative reproduction and sexual reproduction were recorded at the population level along the successional gradient , with increasing competitive conditions. As succession proceeds, we o bserved a decrease in sexual reproduction and an increase in vegetativ e reproduction. At the family level, correlation among traits were sim ilar when plants were grown in the absence of competition and at high density, with a significant negative correlation between sexual reprod uction and vegetative reproduction. For both sprout number and sexual biomass, the performance of families grown under all the treatments wa s positively correlated. Together these results indicate allocational constraints on the reproductive biology of R. acetosella that may be f avoured by natural selection and have influenced population differenti ation along the successional gradient, However, they also revealed tha t the potential exists for evolutionary specialization through plastic ity, in response to variation in environmental conditions.