Population dynamics of the annual plant Senecio vulgaris in ruderal and agricultural habitats

The annual plant Senecio vulgaris has migrated from ruderal to agricultural habitats resulting in weed populations. The population dynamics of S. vulgaris and its naturally associated rust fungus Puccinia lagenophorae were investigated as a basis for the biological control of S. vulgaris with the rust. A detailed basic study at a single ruderal site and a parallel investigation at each five ruderal and five agricultural sites were conducted from April to November 1997. During the whole period of study the spatial distribution of plants was aggregated and plants showed a relatively large size hierarchy as indicated by mean values of the Gini coefficient higher than 0.5. Seedling establishment appeared to be a major factor influencing the dynamics of S. vulgaris. The importance of seedling establishment, together with the observed short generation time of 5 weeks and the broad range of plant sizes at reproduction classifies S. vulgaris as a ruderal strategist. The population dynamics of S. vulgaris differed between the ruderal and the agricultural habitat. Plants of S. vulgaris at the ruderal habitat survived over winter, resulting in greater population sizes (0.1 to 1 of the maximum) and a majority of plants in flower and seed set (81.9%) in spring. At the agricultural habitat, where only a few S. vulgaris winter due to weed control measures, population sizes in spring were smaller (0 to 0.16 of the maximum) with mainly vegetative plants (66.7%). The limited number of suitable hosts at the agricultural habitat in spring lead to a delay of rust infection until August, in contrast to the ruderal habitat where the rust was already present in April. In both habitats mature plant stages were more susceptible to rust infection than vegetative stages. Manipulating the dynamics of the host over winter may enhance rust epidemics in spring serving as biological control of S. vulgaris. S. vulgaris und ihres natürlich vorkommenden Rostpilzes Puccinia lagenophorae in bezug auf die biologische Kontrolle von S. vulgaris mit dem Rost untersucht. Es wurden eine detailierte Basisstudie an einem ruderalen Standort sowie parallel dazu verlaufende Untersuchungen an je fünf ruderalen und landwirtschaftlichen Standorten von April bis November 1997 durchgeführt. Während des gesamten Beobachtungszeitraumes war die räumliche Verteilung der Pflanzen aggregiert, und die Pflanzen wiesen eine relative starke Größenhierarchie, angezeigt durch Durchschnittswerte des Gini Koeffizienten grö