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Jollyville Plateau salamanders are currently listed as threatened under the Endangered Species Act as of September 2013. Populations have declined in urbanized watersheds but remain stable in undisturbed portions of their range.
The ideal habitats for the Jollyville Plateau Salamander are springs, spring-fed streams, and caves with flowing water. Most of the known populations are surface dwelling, or epigean, although this can be somewhat of a misleading classification because the salamanders will retreat to underground refugia during dry periods when the springs no longer flow at the surface.
There also are at least a half dozen caves in the Buttercup Cave system inhabited by salamanders. These salamanders are called troglobites because they spend their entire lives underground (although many may be able to survive on the surface, in which case they would be considered troglophiles). It is unclear whether all cave populations are more closely related to each other than to surface populations, but it is clear that there is variation in morphological appearance among the different populations of cave-dwelling E. tonkawae. Researchers currently are examining the population genetics of this species, which will give more insight into the relationships among the cave and surface populations.
This is a picture of the cross-section of a stream bed when there is no surface flow and the water table has retreated to a sub-surface level. The salamanders retreat with the water level and live under the stream bed until the stream begins to flow again. Down there, they can move between the interstitial spaces created by larger stones below the surface of the stream, as shown in this picture.
The City of Austin initiated an intensive two-year study in 1997 and 1998 to collect baseline information about the JPS. This effort established nine monitoring sites in three watersheds (Bull, Long Hollow, and Shoal) where transects were searched periodically and all salamander observations were recorded (direct count survey). From 1999 to 2003, City of Austin biologists continued to conduct direct count surveys at some of these original monitoring sites, but on a less frequent basis. Beginning in 2004, City of Austin biologists expanded monitoring efforts to include all nine long-term monitoring sites as well as new sites in other watersheds (Cypress, Walnut, and West Bull). The purpose of these surveys was to assess trends in relative abundance, habitat conditions, and seasonal variation in reproduction.
Recent efforts to understand the population dynamics of Jollyville Plateau salamanders began in response to the City’s plan to build a water treatment plant (WTP4) at the headwaters of Bull Creek, an ecologically-sensitive area and home to many large populations of salamanders. This included a mark-recapture survey that tagged salamanders so they could be studied at three different sites to compare the effects of the proposed water treatment plant before and after construction. In the past, all monitoring was conducted by periodically counting all salamanders observed in a given area. However, this method did not take into consideration capture probability (the likelihood of capturing an animal that is present), which can have a large effect on estimated population size. Mark-recapture allows for estimation of capture probability, and thus, much more accurate approximations of population size in addition to estimates of survival and migration.
In December 2007, the City Council voted to purchase an alternate site to move WTP4 out of the Bull Creek watershed. However, the mark-recapture portion of the study is still ongoing, although with less frequent sampling.
Most of what we know about the ecology of Austin’s aquatic salamanders is from studies conducted by the City of Austin on the more easily accessible surface populations. Their diet, like most salamanders, is entirely carnivorous. Based on field observations, fecal content analysis, and new radio-isotope data, they eat a variety of prey that is likely based on both what is available and what fits in their mouth. This includes a variety of snails (Gastropoda), seed shrimp (Ostracoda), copepods (Copepoda), amphipods, insects (such as midge, mayfly, and damselfly larvae, aquatic beetles, etc.), flatworms (Planaria), segmented worms (Annelida), and others.
Amphipods in Eliza Spring.
Barton Springs Salamander eating Amphipods
Relationships between the salamanders and their predators are not well understood. Some evidence suggests freshwater sunfish and basses opportunistically feed on salamanders. In the past, many salamander habitats were too shallow to harbor these fish species. Now these fishes have more available permanent and stable habitat in salamander streams because of direct and indirect stream channel modification by humans (e.g. dams creating Barton Springs Pool). Predatory fish presence may hinder dispersal where unnatural intermittent pools intercept the stream pathways that were once more shallow riffles or runs. Recent evidence clearly shows that chemical cues from predatory fish can negatively affect salamander activity.
Crayfish are common in both shallow and deep waters and can be found in nearly every salamander habitat. Crayfish are generalist predators, eating a variety of things from fish and tadpoles to plants and detritus, and have been observed feeding on juvenile Barton Springs Salamanders.
So, it is not unlikely that they are also a common Jollyville Plateau Salamander predator. Interestingly, the burrows created by crayfish may be beneficial in some ways to Jollyville Plateau Salamanders. One theory is that crayfish burrows may act as a path for salamanders to retreat through dense sediment and gravel to reach subsurface waters during dry periods.
Other large invertebrates have been observed feeding on salamanders. Giant water bugs (Lethocerus uhleri) are large ambush predators (up to 65mm) and have been seen at several monitoring sites preying on salamanders, ranid tadpoles, and mosquito fish (Gambusia affinis).
Damselfly larvae of the genus Archilestes are long and slender ambush predators that prey on very small juveniles if given the opportunity.
Cannibalism has also been documented in this species. Adults have been observed regurgitating the remains of juvenile salamanders when captured. This in part helps to explain why juveniles are often found in areas where adults are not, such as in very shallow water on the edge of the stream.
Unlike the surface populations, cave-dwelling Jollyville Plateau salamanders are the top predators of that ecosystem. The downside, however, is that prey availability is much lower. Because all troglobitic organisms live in total darkness, there are no primary producers, so they must rely on nutrient input from the surface. The salamanders likely feed on available troglobitic and troglophilic (can live inside and outside caves) crustaceans and insects and potentially accidental prey washed into the caves during rain events.
WQRS COA-ERM 1999-01 Jollyville Plateau Water Quality and Salamander Assessment
SR-03-02 Jollyville Salamander Analysis
CM-07-01 Mark Recapture Study 2007
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.