Introduced fish assemblages in a mosaic of urban ponds: evidence for species-area and diversity-dominance patterns

We studied species-area and diversity-dominance patterns in fish communities of a mosaic of urban ponds (Rome, Italy). We detected 10 fish species (all introduced) in 40 isolated ponds (12.9% of the total; n = 311). The log-transformed species-area relationship (logS = 0.04 logA + 0.16) was significant. Assuming the lack of mechanisms of natural immigration between totally isolated ponds, the number of fish species in this mosaic of ponds may depend exclusively on progressive extinctions and on random and arbitrary events of introduction (acting as human-mediated immigration), these latter explaining the apparently low taxon-related isolation indicated by a low z value (= 0.04). We observed a significantly lower number of species in the smallest ponds and a further threshold under 1 ha in size: these values could represent an interesting threshold for pond management. The diversity-dominance approach evidenced pond size effect acting as a factor of stress on these assemblages