As urbanization increases across the globe, more ecologists have taken note of its consequences to stream systems. Sufficient data have been collected to document repeated patterns in urbanized streams for many abiotic parameters, aquatic insects, and fish. For example, we now know that urbanized streams experience more frequent and intense spates as a result of increased runoff form impervious surfaces in the urban watershed. The spates eventually lead to a more incised and wider stream bed. Such abiotic shifts consistently result in decreased aquatic invertebrate and fish diversity. More recently, stream-breeding salamanders have been observed to decrease in density in urban areas. We monitored the density of southern two-lined salamanders for the duration of two cohorts in 12 streams in western Georgia, USA. We then used path analysis to determine the relationships between land-use change, abiotic shifts in the stream environment, and larval salamander density.

Results/Conclusions

We found that southern two-lined salamanders in the streams we monitored exhibited no change in reproductive output between urban and reference habitats. However, repeated sampling throughout the larval period revealed a large decline in density of larvae in urban areas prior to metamorphosis, while a similar decline was not seen in reference habitats. We evaluated several hypotheses that might explain the observed decline in urban areas, and a model in which increased impervious surface causes an increase in spate frequency and magnitude, which then leads to decreased larval density had the most support. This is the first attempt to compare multiple plausible hypotheses as to why salamander density and diversity decreases in urban habitats. By describing larval density at the beginning and end of the larval period, and by identifying a likely mechanism for the observed decline in density, species-specific and stream restoration efforts can be enhanced.