Nischendifferenzierung zweier nah verwandter Neophyten im urbanen Raum

The alien Galinsoga ciliata and G. parviflora are widely distributed in Switzerlandin rural as well as urban areas. They are both regarded as weeds, are oftensympatric and grow in similar ecological settings. In urban environments, the otherwiseslight ecological differences between species appear to be more expressed,but quantitative studies analyzing the distribution pattern, habitat and substratepreferences of both species were missing. In the city of Basel (Switzerland) Galinsogaciliata (Raf.) Blake and G. parviflora Cav. were mapped onto a 500 m3500 mgrid. 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 Baselmuch later than G. parviflora.In contrast to G. parviflora, which was absent in the peripheral areas of thetown, the stands of G. ciliata were spread over the whole town area. Despite thefact that both species prefer nutrient- and humus-rich soil and coexisted in nutrientrichhabitats in the city of Basel, G. parviflora grows more often in pavement gapsand crevices of stones, concrete or asphalt than G. ciliata. The lower frequency ofG. parviflora, its smaller aggregations, and the exploitation of the most extremehabitats demonstrate the weak competitiveness compared with G. ciliata.Hence, in urban areas, where the growth conditions for the two weed speciesare not optimal, G. parviflora could maintain its presence by showing a clear nichedifferentiation compared to G. ciliata. Betr. die Ausbreitung von zwei Galinsoga-Arten in Basel