Urbanization and biotic homogenization.
Klotz, Stefan*,1, Kuehn, Ingolf1, 1 UFZ-Centre for Environmental Research Leipzig-Halle, Halle, Germany
ABSTRACT- The translocation of organisms across biogeographical barriers leads inevitably to the homogenization of formerly distinct biota on global scale as global species pool and area are limited. This means, that biota of separated biogeographic regions become more similar due to an increasing number of shared species.We tested whether biological invasions would lead to biotic homogenization in local floras in Germany. We randomly selected 30 grid cells (ordnance survey maps, 10 min. longitude by 6 min. latitude, c. 130 sqkm) and calculated the similarities for native species, archaeophytes (pre 1500 aliens) and neophytes (post 1500 aliens) among the grid cells. Then we calculated the differences between the particular native and alien floristic similarities. Significance was assessed by Fisher paired comparison test (with 999 randomizations). The complete procedure was repeated 1000 times. As indices of similarities are influenced by species richness, we choose Simpson Similarity (S= a/[a+min(b,c)], where a is the number of common species while b and c are those unique to one grid cell or the other). This is probably the similarity index which is least influenced by species richness.We further tested the effect of urbanization on biotic homogenization, i.e. we wanted to know whether urbanized areas are more similar than rural areas. We choose all grid cells with more than 1/3 urbanized areas (60 grid cells) and compared the results to 1000 x 60 randomly selected grid cells (using the methods described above). As cities are not randomly spread across Germany and as similarities are influenced by the distance among compared floras, we had to correct similarities by distance using residuals of ordinary least square regressions. We found that urbanized areas do not differ significantly in their floristic similarities from rural areas. Partitioning this into the different groups according to the immigration status, we get a different picture: Native and archaeophytic floras of urbanized areas are more similar than those of rural areas. Neophytic and alien (pooling archaeophytes and neophytes) floras of urbanized areas are less similar (i.e. more distinct) than those of rural areas.
Key words: biotic homogenization, urbanization, alien species
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