Like the other two salamanders endemic to Austin, Texas, there are several different reasons why the Jollyville Plateau Salamander is threatened.
First, the species is found in a very narrow geographic area. While not as restricted as the Barton Springs or Austin Blind salamanders that only are found in one closely spaced group of springs, the Jollyville Plateau Salamander is confined to the springs, spring-fed streams, and wet caves in and around northwest Austin, which is still a relatively small area for the entire worldwide distribution of one species (range map). Having a small range makes it inherently more susceptible to extinction because catastrophic events (natural or anthropogenic) can have a much larger impact on population size than they would for a wide-ranging species.
Second, increasing development has negatively affected salamander habitats and thus relative abundance has decreased in the recent past. Finding a direct cause and effect relationship between salamander population declines and the multitude of changes that occur with development is difficult to do, in part because of the complexity of the problem, but also because proper scientific rigor requires ample sample sizes, replication, and often experimental modification: three things conservation biologists do not usually have when studying threatened or endangered species. However, it is clear that sites with the most urban development support the fewest number of salamanders, and that several of these sites have experienced declines since monitoring began in 1996. Salamander deformities have also been observed at one urban monitoring site that has exhibited unusually high levels of nitrates.
The figure below shows the results from direct count surveys between 1997 and 2008. The Bull Creek Tributary 6 site was an area of increasing development, with a 10 percent increase in impervious cover between the years 1995 and 2003. You can see that between 2002 and 2008, counts are on average lower than those from previous years. Although there are many factors that could cause this observed decline in counts, this trend has also been observed at several other monitoring sites that are within urbanized watersheds, but has not been observed within rural ones.
One effect urban development has on the aquifer and watersheds of these salamanders is an increase in frequency and velocity of stormwater runoff during rain events. You might think that more water would be good for an animal that spends its life in water. However, increased flow can the effect of scouring a stream, removing the cobble and gravel substrate the salamanders use for cover and to lay their eggs. Runoff also brings a plethora of contaminants from the roadways and people’s yards, including increased sediment loads from construction projects and dangerous chemicals found in gasoline, motor oil, lawn care products, and driveway sealants.