When adults of a species defend feeding territories, juveniles may benefit from access to those territories during periods when prey decline between territorial spaces. Adults may either deny or allow such access, thus impacting the foraging success of the juveniles. We examined a dense population of the terrestrial red—backed salamander (Plethodon cinereus) in which male and female adults hold territories (cover objects on the forest floor that act as patches of moisture and prey during rainless periods) that should be attractive to juveniles as the surrounding leaf litter dries. The purpose of our research was to determine whether adults of P. cinereus exclude juveniles from their territories, as they do consexual adults, and to explore how juveniles respond to adult territoriality. We found that adults were uniformly distributed intrasexually under cover objects but positively associated intersexually, during the summer when courtship does not occur. Juveniles entered territories of some adults during dry weather, when foraging in the leaf litter was difficult (out of territories) during rainy periods, when prey were more available. Adult ingested significantly larger prey than juveniles but food niche overlap was larger between juveniles and adults, suggesting that competition for limited prey occurs when they share territories during rainless periods. In laboratory experiments, juveniles were attracted to territorial pheromones of adult males and females, and males were less aggressive toward such juveniles than toward intruding adult males. Adults were more tolerant of juveniles with which they had cohabited previously in the forest than of juveniles that were "strangers."; in turn, juveniles spent more time near and less time escaping from previously cohabiting adults than from adult "strangers" Thus, adults appeared to tolerate territorial intrusions by juveniles but were more tolerant of juveniles than of others. We examine several hypotheses that may explain why adults might allow certain juveniles into their feeding territories during stressful periods. Our data best fit a "kin recognition" hypothesis. Kin recognition is known to occur in other species of salamanders and, in our study, adults and juveniles that had previously cohabited on the forest floor were more benign toward each other than were those had not cohabited. Our data do not favor the "no competition" hypothesis because juveniles entered adult territories just when both adults and juveniles were able to ingest fewer prey (dry weather). Our results do not favor the hypothesis that juveniles sneak into adult territories undetected because juveniles more into adults' territories when adults are present, and histological evidence suggests that juveniles possess glands used in social communication. We do not favor the hypothesis that adult habituate to cohabiting juveniles because habituation is not likely to occur between food competitors when the adults can easily defeat the juveniles. The hypothesis of "dear enemy" (neighbor) recognition, w...

In terrestrial plethodontid salamanders, aggressive behaviour is thought to function in the spacing of territorial residents among contested cover objects on the forest floor. Such behaviour, when exhibited toward heterospecifics, plays an important role in the competitive interactions between species. We compared levels of aggressive behaviour in intra- and interspecific contexts in two species of sympatric salamanders (Plethodon ouachitae and P. albagula) that have similar ecological requirements but differ in adult size. We also tested the effectiveness of such behaviour in holding cover objects (territorial foci) in the laboratory and on the forest floor. We predicted that if one species were more aggressive than the other, then that species would have greater success in obtaining and holding cover objects. In laboratory trials, residents of P. ouachitae (the smaller species) were extremely aggressive in both intra- and interspecific contexts. Individuals of P ouachitae delivered bites at a rate 14 times that of previously studied species of Plethodon and were significantly more likely to escalate to biting when tested as territorial residents (in intra- and interspecific trials) and as intruders (in interspecific trials). Plethodon albagula exhibited a lower level of aggression, similar to other species of Plethodon. In laboratory trials, in which salamanders competed for cover objects of differing quality, residents of P. ouachitae were effective in expelling conspecific intruders, and they were marginally effective at expelling intruding P. albagula. Residents of P. albagula were less effective in expelling conspecific intruders and did not expel intruding P. ouachitae. We conclude that the extreme aggression exhibited by P. ouachitae enabled it to expel intruders from artificial cover objects and to invade cover objects held by larger heterospecific residents. Field data supported intraspecific defence of cover objects by P. ouachitae, but results for P. albagula were inconclusive. These results are consistent with the geographic distributions of these species (P. ouachitae typically outnumbers P. albagula in the Ouachita Mountains) and provide an example of a behavioural mechanism overcoming a size-related disadvantage.

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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