Robert G. Jaeger
We can find the thesis statement of the article at the end of the abstract. The author of the article “Distributions of two species of terrestrial salamanders” supposes that the competitive exclusion by cinereus restricted the distribution of Shenandoah to the suboptimal talus refugium. That means that according to Jaeger the salamander Plethodon richmondi shenandoah is excluded from the soil by another species of salamander, P. cinereus.
To test the hypothesis that the former species is restricted from the habitat by another one, the researcher constructed enclosures in the four habitats in Shenandoah National Park, Virginia. The study area of the article involves the discussions of different researchers about the competitive exclusion principle among the species in the environment. The interspecific competition plays a vital role in the distribution of species in the nature as we can conclude basing on the article.
To draw conclusions, the researchers suggested testing four different habitats:
Type-I talus composed of bare rock slides where no soil was present between the rocks.
Type-II talus, where the surface of the ground was rocky but soil had settled only between rocks. There was some shade provided by a few canopy trees and vegetation on the ground. The temperatures were stable and moisture was retained much longer than in Type-I talus.
Type-III talus consisted of rocks mixed with shallow soil, moisture was retained for a long time due to the presence of soil, and the vegetation was similar to that outside the talus.
The soil outside the talus that averages 3.5 times as deep as soil in Type-III talus.
To prove the hypothesis the researcher compared the survivorship of the two species. For this purpose they were put in three enclosures with isolated shenandoah, isolated cinereus and one with mixed type for each of the habitats (Type-I, Type-II, Type-III and soil outside the talus). Jaeger used an exclusion experiment on the north-facing slope of the Hawksbill Mountain and the one-tailed Kolmogorov-Smirnov two-sample test to analyse the data as the methods for their research.
For the experiment and on having collected the data for analysis, Jaeger checked the number of salamanders remaining in each enclosure every week and took notes for twelve weeks. This period of time was enough to provide sufficient information for conclusions concerning the distribution of salamanders. Jaeger placed salamanders in enclosures in June 1967 after a heavy rain and expected to terminate the experiment at the end of August or if all the species died before the scheduled time.
The data recorded each seven days was analysed by one-tailed Kolmogorov-Smirnov two-sample test. According to the test, the animal which survived for a longer time scored higher than the one that survived for a shorter time. Here are the brief conclusions that we can see from the figures in the article:
No animals survived in the extremely dry talus. That means that both species cannot survive in this particular habitat for a long time.
Shenandoahs’ mortality was less in relatively dry talus for both isolated and mixed groups. That means that such …