Coexistence of Salamanders in the Genus Plethodon: A Variation of the Santa Rosalia Theme

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Abstract
Two sympatric species of Plenthodon (P. hoffmani and P. punctatus), dissimilar in size as adults, were used to investigate the general problem of how two species that differ in size as adults but overlap in certain life history stages may avoid significant, size—related overlap in ecological requirements. The following three hypotheses were tested: (1) that size differences between adults lead to resource partitioning adequate to explain the coexistence of adults; (2) that co—occurring, similarly sized juveniles of the large species and adults of the smaller lack significant resource partitioning; and (3) that alternatives to resource partitioning are likely to be of importance in promoting coexistence in these salamanders. Analysis of food and surface habitat utilization shows overlap values that are low enough for adults of the two species to coexist but too high for coexistence between juveniles of the larger species and adults of the smaller. Because subadults and juveniles make up a substantial proportion of the population of the largest species, it appears that salamanders with long developmental periods and without temporal staggering during periods of development, probably cannot use adult size differences alone as an avenue along which to ameliorate interspecific competition for food or space. On the other hand staggered feeding schedules (noncoincident feeding) in all individuals, coupled with the partioning of the structural habitat by adults of the two species, appear to be factors of major importance in reducing inter— and intraspecific competition.