INTRA- AND INTERSPECIFIC CHARACTERIZATIONS OF BURROW USE AND DEFENSE BY JUVENILE AMBYSTOMATID SALAMANDERS

We conducted two laboratory experiments with juveniles of Ambystoma opacum and A. maculatum to test for intra- and interspecific competition for burrows. Experiment 1 examined how the behavior of an intruder (i.e., an individual that enters an occupied burrow) was influenced by the presence of a resident salamander that had been placed in the test chamber 5 d earlier. In Experiment 2, we investigated patterns of cohabitation when salamanders were introduced singly, as conspecific pairs, or as heterospecific pairs during a 7-d test period. The results of these experiments indicate that (1) when maintained alone, juvenile A. opacum were observed more frequently outside of the burrow than were juvenile A. maculatum; (2) A. maculatum were more likely to enter unoccupied burrows compared to burrows that were occupied by conspecific or heterospecific salamanders; (3) A. maculatum intruders were bitten more frequently by resident A. opacum than by resident A. maculatum; (4) when two individual salamanders shared a burrow, A. maculatum were more likely to leave a cohabited burrow whereas use of shared burrows by A. opacum was not influenced by the presence of another salamander in the burrow. These experiments demonstrate that juvenile A. opacum may defend burrow space by excluding heterospecific salamanders. However, our results also indicate that species-specific behavioral differences may influence patterns of burrow use, which may reduce the importance of agonistic interactions under natural conditions.