The Experimental Test of an Analysis of Field Distributions: Competition In Terrestrial Salamanders

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Abstract
Experimental removal of the terrestrial salamander Plethodon jordani from marked plots in the Great Smoky Mountains and the Balsam Mountains of North Carolina, USA resulted in statistically significant increases in the abundance of P. glutinosus in both areas. The increase appeared earlier in the Smokies, where the two species overlap by only 70—120 m. Removal of P. glutinosus the less abundant species, did not result in a statistically significant increase in P. jordani, but did increase the proportion of young in that species. Again, the effect was more pronounced in the Smokies than in the Balsams, where the altitudinal overlap is 1220 m (4000 ft). Stronger competition in the narrow zone of overlap had been predicated on the basis of field distributions, but a measurable level of competition in the wide zone of overlap was surprising. The experiments permitted the direct calculation of coefficients of competition and carrying capacities for both species in both areas. Competition coefficients were higher in the Smokies, but carrying capacities were very similar in the two areas. The experimental approach eliminated the assumptions required for calculating competition coefficients by resource partitioning, and since the experimental design was published before the experiments were begun, the circularity implicit in retrospective analyses was avoided.