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Is the proportion of alien species in urban habitats influenced by city size?



Rok publikování 2015
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Popis Although cities are centres of introduction of alien species, the role of their dispersal limitation compared to invasibility of urban habitats is still unknown. We assume that city size could be used as a proxy for dispersal limitation. We suppose that large cities with high traffic, industry and high population density will host on comparable plots more alien species than small cities due to higher availability of dispersal vectors and of seed sources. Data sampling was carried in three types of human settlements – cities with more than 100 000 inhabitants, towns with population between 20 to 50 000 inhabitants and villages with less than 5 000 inhabitants. All settlements are situated in Central Europe. In each settlement, three habitat types were chosen – paved settlement centre, residential area and abandoned area with perennial grassland and shrubs. Plots of 1-ha size were sampled in each habitat type by recording all spontaneously occurring taxa of vascular plants. Recorded species were divided according to their origin and residence time to native species, archaeophytes and neophytes. We found that total species number in studied habitats is affected by city size. The proportion of neophytes increases with city size especially in residential areas, where human activities serve as a source of propagules of neophytes. In contrast, the proportion of archaeophytes does not vary with size of the settlement. Archaeophytes are well established part of flora of cities and their surroundings and as such they are not dependent on the repeated human introduction to urban habitats. Proportion of native species varies according to habitat type. In centres native species are underrepresented in large settlements, we suppose that this is result of isolation from surrounding landscape. The opposite pattern was recorded in residential areas and abandoned areas, which are situated closer to the edge of settlements.
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