Habitat Separation Between Sympatric Snake Populations

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Abstract
Quantitative data consisting of 14 structural habitat variables and 5 climatic variables were obtained from 505 telemetric relocations of 21 timber rattlesnakes (Crotalus horridus) and 20 northern copperheads (Agkistrodon contortrix mokeson) in eastern Pennsylvania. Multivariate analysis of variance revealed that the habitats utilized by the two species differed significantly. The single discriminant function generated by a discriminant analysis was highly correlated with variables describing structural features of the forest floor and canopy. A. c. mokeson utilized relatively open areas with higher rock density and less surface vegetation than did C. horridus. The discriminant function correctly classified 76% of the samples. The 24% overlap consisted largely of locations from gravid C. horridus whose habitat preference closely paralleled A. c. mokeson. Measurements of habitat overlap indicated that the separation of the two species along the habitat axis was theoretically sufficient for competitive avoidance. Although the observed species separation can be interpreted as reflecting interspecific competition, an alternate explanation based upon inherent physiological differences is also presented.