Summary 1.When studying speciation, researchers commonly examine reproductive isolation in recently diverged populations. Polymorphic species provide an opportunity to examine the role of reproductive isolation in populations that may be in the process of divergence. 2. We examined a polymorphic population of Plethodon cinereus (red-backed salamanders) for evidence of sympatric ecological separation by colour morphology. Recent studies have correlated temperature and climate with colour morphology in this species, but no studies have looked at differences in diet or mate choice between colour morphs. We used artificial cover objects to assess salamander diet, mating preference and surface activity over a 2-year period at a field site in northeastern Ohio. 3. We detected differences in diet between two colour morphs, striped and unstriped. The diets of striped individuals were significantly more diverse and were made up of more profitable prey than the diets of unstriped salamanders. 4. Opposite sex pairs were made up of individuals of the same colour morph and striped males were found more often with larger females than were unstriped males. 5. We corroborate findings of earlier studies suggesting that the unstriped form is adapted to warmer conditions. Unstriped individuals were the first to withdraw from the forest floor as temperatures fell in the late fall. We found no evidence that the colour morphs responded differently to abiotic factors such as soil moisture and relative humidity, and responses to surface temperatures were also equivocal. 6. We conclude that the two colour morphs exhibit some degree of ecological separation and tend to mate assortatively, but are unlikely to be undergoing divergence given the observed frequency of intermorph pairings.

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Red-backed salamanders, Plethodon cinereus, use territorial advertisement in the form of agonistic displays and pheromonal scent marking as a mechanism for intraspecific interference competition. Although ecological and behavioral interactions among species of salamanders have been well studied, little is known about the interactions between territorial P. cinereus and other ecologically similar species, such as large predatory invertebrates. Our field data indicate that P. cinereus and a large syntopic centipede, Scolopocryptops sexspinosus, exhibit negative spatial associations in natural habitats, possibly indicating interspecific territoriality. Only seven instances of salamander/centipede co-occurrence were recorded from a field sample of 247 occupied cover objects. Cover object size was positively correlated with salamander SVL (tip of the snout to the anterior end of the cloaca), but there was no correlation of cover object size to centipede length. Data on the ability of P. cinereus to differentiate among chemicals on the substrate suggest that visual cues are not necessary to elicit a territorial response from intruding salamanders. Although in laboratory trials salamanders behaved similarly toward intruders of both species, biting was directed only toward centipedes. Salamanders spent significantly more time approaching centipedes than they did approaching other salamanders. Approach behavior was often associated with nose tapping and may be an investigative, rather than aggressive, behavior. We suggest that territorial P. cinereus respond similarly to intruding salamanders and centipedes, but that they escalate more readily to biting centipedes because S. sexspinosus is sightless and thus unable to respond to visual signals.

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