Nischendifferenzierung zweier nah verwandter Neophyten im urbanen Raum

Abstract

The alien Galinsoga ciliata and G. parviflora are widely distributed in Switzerland in rural as well as urban areas. They are both regarded as weeds, are often sympatric and grow in similar ecological settings. In urban environments, the otherwise slight ecological differences between species appear to be more expressed, but quantitative studies analyzing the distribution pattern, habitat and substrate preferences of both species were missing. In the city of Basel (Switzerland) Galinsoga ciliata (Raf.) Blake and G. parviflora Cav. were mapped onto a 500 m x 3500 m grid. At each locality population density, habitat and substrate type were recorded. G. ciliata was more wide-spread and seven times more frequent than G. parviflora. These differences existed despite G. ciliata being introduced to Europe and to Basel much later than G. parviflora.

In contrast to G. parviflora, which was absent in the peripheral areas of the town, the stands of G. ciliata were spread over the whole town area. Despite the fact that both species prefer nutrient- and humus-rich soil and coexisted in nutrient-rich habitats in the city of Basel, G. parviflora grows more often in pavement gaps and crevices of stones, concrete or asphalt than G. ciliata. The lower frequency of G. parviflora, its smaller aggregations, and the exploitation of the most extreme habitats demonstrate the weak competitiveness compared with G. ciliata.

Hence, in urban areas, where the growth conditions for the two weed species are not optimal, G. parviflora could maintain its presence by showing a clear niche differentiation compared to G. ciliata.