Author: Matthew Samuel Pugh

Decline of the Green Salamander: Corser’s Study on Aneides aeneus

Posted on by Matthew Samuel Pugh


In Corser’s (2001) peer-reviewed article regarding Aneides aeneus, a green salamander species found in the Appalachian Mountains, he found that the species suffered critical population declines during different periods spanning across multiple decades. The first decline was noticed in the 1970s, with another major decline found in the late 1990s. Corser attributed these population losses to habitat destruction, overcollection, climate change, and epidemic diseases.

Most amphibian species that have declined in North America are those found in mountainous regions experiencing localized population decreases. These are typically isolated populations, separate from others, representing a localized population decline rather than a species-wide collapse. Additionally, other amphibian species outside of salamanders were found to have even worse population declines due to their (at the time) lack of understanding regarding salamander populations. During the 1990s, following reports of amphibian declines, many researchers were first introduced to the concept of amphibian decline as a present conflict in wildlife ecology (Corser, 2001).

This article focused on a specific species throughout the 1990s when this new issue was brought to the forefront of the wildlife conservation community. Corser chose to study Aneides aeneus, a green salamander found in the “Blue Ridge Escarpment” or BRE. The Blue Ridge Escarpment, according to VisitGreenvilleSC.com, is “the line at which…the Blue Ridge Mountain range plunges down towards the rolling foothills of South Carolina,” which illustrates the interesting ecological niche that these salamanders play a role in. According to Corser (2001), they “occupy one of the most specialized and xeric niches of any eastern salamander.” They live in crevices and short outcroppings along tributaries and gorges of the BRE.

Due to the increased observation of salamander decline apart from the first observed drops in 1970, Corser (2001) chose to observe and collect data to determine the population sizes in the BRE. In areas found along the BRE in Georgia, North Carolina, and South Carolina, Corser located the previous scientist’s survey locations from the 1970 study and attempted to recreate the same observations. Corser found thirteen locations to monitor the green salamander populations, seven of which were exactly from Snyder (1971). This gave Corser both new and previous observational areas to research the rock crevices for brooding females. This method was proven to be significant for Snyder’s (1971) research. Corser surveyed these areas once a year from 1991 to 1999, during the last week of July or the first week in August. This provided a great opportunity to locate brooding females and estimate both population size and fecundity.

By using the MONITOR Monte Carlo linear regression model, Corser (2001) was able to determine that the population decline at the historic sites from Snyder’s (1971) paper remained low and continued to decline. In contrast, the new populations found during the 1991 to 1999 survey period were not significantly declining when compared to the already decimated populations from the 1971 observations.

Finally, Corser (2001) was able to conclude that a myriad of factors—whether that be clear-cutting, habitat loss, increased levels of DDT in salamander systems, or other anthropogenic influences seen in nearby amphibian species—might be contributing to the decline and lack of population rebound. With the limited number of sample sites and a rejection of the null hypothesis for the green salamander populations, one could conclude that there are likely many unknown areas Corser was not able to find, since their ecological niche is so specific and difficult to locate within rock crevices. If more samples were found and observed over longer periods of time, future studies could see more significant results, one way or another. This could further prove that their populations are, in fact, declining and are unable to rebound from ongoing environmental and human-caused stressors.

References: Corser, J. D. (2001). Decline of disjunct green salamander (Aneides aeneus) populations in the southern Appalachian Mountains. Biological Conservation, 97(2), 119–126. https://www.sciencedirect.com/science/article/pii/S0006320700001002?via%3Dihub

Snyder, D. H. (1971). The function and evolution of brooding behavior in the plethodontid salamander Aneides aeneus. Copeia, 1971(2), 385–390. www.visitgreenvillesc.com/listing/blue-ridge-escarpment/6237/

Urban Waterfowl Population Management

Posted on by Matthew Samuel Pugh

Overview & Background: In the peer-reviewed journal article Urban waterfowl population: Ecological evaluation of management and planning (Greer, 1982), we see urban ducks observed and studied in order to determine early morning congregation habits and location. This study followed these populations, which consisted primarily of mallards, in Puyallup, WA. As we see more and more urban development in areas with adjacent rural habitats, waterfowl and other vertebrates are forced to adapt to stricter conditions. In these areas, waterfowl struggle with several habitat-related issues, such as habitat size and nesting condition/success. Many factors play into these aspects of survival in urban environments. Without proper habitat size or conditions that resemble the complexity of more rural areas, we see less species diversity.
Methods: The researchers took vegetation surveys and waterfowl counts in four locations in the Washington area. The four locations were: Dairy Stream, Pumphouse, Dairy Lagoons, and DeCoursey Pond. The vegetation surveys showed an abundance of reed canarygrass, turf grass, and pasture grass. Cover, frequency, and dominance were values that Greer calculated from these surveys. Along with the vegetation sampling, there were waterfowl head counts and monitored nesting success observations. Over the course of 14 months, Greer counted and collected data on the number of waterfowl found in these four locations at predictable times in the morning. The Shannon Index was used to determine the species diversity in these areas. For statistical analysis, ANOVA, Duncan’s multiple range test, and discriminant and cluster analysis were utilized.
Results: Over the course of the survey, Greer observed 13 different species of waterfowl, with mallards being the most abundant. They were also found to be the only species nesting locally. Other species, such as American wigeon, bufflehead, scaup, and gadwall, were present seasonally but did not nest in the study area.

The Dairy Stream location was somewhat supportive of several species such as mallards, wigeons, and buffleheads. However, the most supportive location was DeCoursey Pond. It had the highest species diversity and supported both dabbling and diving ducks due to the pond’s size and complexity compared to the others. The Dairy Lagoons primarily housed mallards, with low diversity for other species, though diversity improved slightly when mallard numbers were less dominant. Finally, the Pumphouse had the lowest species richness and was mostly dominated by mallards when feeding occurred. There was very little nesting success overall, and nesting was only attempted by mallards. This was due to low nesting cover, disturbance, and intraspecific aggression from other mallards. In all, DeCoursey Pond was the most complex and deep site, resembling rural environments that waterfowl were more adapted to, which provided a greater opportunity for them to thrive. By contrast, the lower diversity areas such as the Pumphouse were more frequently disturbed by humans and interfered with the natural behavior of more sensitive species.

Reflection/ Critique: After reading over the study and its findings, I have a few comments and possible improvements. I thought the vegetation sampling was conducted well and helped contextualize the environments these waterfowl were around and what they were interacting with. This gives clues to how and why species diversity might be so different in one area compared to the next. However, one area I thought was understudied was the possible predator or human interaction with the waterfowl. Predators, especially urban wildlife predators, could be a significant factor influencing lower species diversity in some locations. If predators were observed, one could determine if this was a factor in the counts of waterfowl in these areas. Artificial feeding also seemed to alter species composition at the Pumphouse, and this might have been worth more systematic study. For the most part, I thought it was a great survey that was done several decades ago but still represents a classic observation-based study that gives insightful data for those looking at how waterfowl might use urban corridors to live in.
Citation:
Greer, D. M. (1982). Urban waterfowl population: Ecological evaluation of management and planning. Environmental Management, 6, 217–229. https://doi.org/10.1007/BF01866885