THE STATUS OF INDIVIDUALS WITHIN A CHANGING PLANT POPULATION AND COMMUNITY: THE EXAMPLE OF SENECIO RIVULARIS (ASTERACEAE)

摘要

A population of Senecio rivularis (Waldst. & Kit.) DC. in the Roztocze National Park (SE Poland) was studied in 1987-2002 for the following purposes: (1) to estimate the absolute age of individuals in different parts of the population, their fecundity, and contribution to the reproduction of the whole population; (2) to assess the stability or variability of the size and stage structures over time; and (3) to find out whether simple measures such as means, variance, skewness and kurtosis can be usedto characterize the dynamics of the plant size distribution. The absolute age and fecundity of individuals were higher at the population margins, suggesting that those plants make a greater contribution to the total reproduction of the population, and thus are responsible for genet abundance and population dynamics. Over the study period, a significant decrease of juvenile genets was observed in the whole population, accompanied by changes in the fraction of generative plants. Changes in the share of juvenile and flowering ramets varied between parts of the population area. This means that the studied population may be divided into small-scale patches with their own dynamics. Size structure, characterized by such parameters of flowering plants as stemheight, leaf rosette dimensions and number of heads per umbel, was determined to be a very dynamic property. All the differences between years were statistically significant, but a temporal trend of changes was observed only for rosettes.