Effects of Conspecific Density on Habitat Assessment and Exploratory Behavior in Eastern Red-backed Salamanders (Plethodon cinereus)
Territory selection is critical to foraging, courtship, and numerous other aspects of vertebrate ecology. We tested the effect of conspecific density on territory choices and exploratory behavior in Eastern Red-backed Salamanders (Plethodon cinereus) given choices of unfamiliar territories marked by single, multiple, or no conspecifics. We tested two alternative hypotheses: 1) the presence of conspecifics signals high-quality habitat, because it appears to support one or more individuals, and 2) the presence of conspecifics signals effectively low-quality habitat, because that habitat is already occupied and therefore subject to higher levels of competition. Focal salamanders tended to enter unoccupied territories more frequently than those marked by an individual conspecific, but did not spend more time in unoccupied territories than those marked by individuals or groups. However, they spent more time in individual-marked territories than group-marked territories. Intruding salamanders exhibited a lower head move rate in individual-marked territories than in group-marked or unoccupied territories. Intruding females were more likely to enter shelters within territories, regardless of whether they appeared to be occupied, and made fewer large movements while in territories, than intruding males. These results suggest there is a greater perceived cost to intruding P. cinereus of inhabiting territories occupied by multiple conspecifics than territories occupied by individual conspecifics. Our study suggests that the net benefit of entering an occupied territory is lower for male salamanders compared to females and this difference likely stems from the greater value of shelters to females or a higher risk of competition for males.Abstract
Schematic scale drawing of the arenas used for experimental trials as viewed from above. Distances from the lower left corner of the arena are in centimeters. Partial circles at each end represent choice areas, hatched rectangles represent cardboard shelters, and small black rectangles represent fecal pellets.
Effect of territory social status on territory preference of focal salamanders as indexed by number of times a salamander entered a choice area (A–C) and amount of time spent in a choice area (D–F). Each panel presents results of choice trials under each treatment condition (control vs. individual; control vs. group; individual vs. group) for all focal salamanders in the experiment (A and D), for females only (B and E), and for males only (C and F). Each data point represents the difference between choices exhibited by an individual salamander as indicated by the x-axis labels, which are to be read as control minus individual (C − I), control minus group (C − G), and individual minus group (I − G). For example, positive values for C − I indicate higher values for the C treatment than the I treatment. Overlapping points are jittered on the x-axis to improve visibility. Sample sizes for each analysis are indicated above the top panels. P values are from permuted paired tests.
Variation in exploratory behavior among focal salamanders once inside a choice area. Means and 95% confidence intervals are shown; these values are from raw data and are not adjusted for effects of other variables in the models. Open circles = females; closed circles = males. Asterisks indicate significant effects based on permuted linear mixed effects models. In the case of treatment, a Bonferroni correction was applied to account for tests of each level of treatment, and where applicable, the level that was found to be significant after the Bonferroni correction is indicated in parentheses. See Table 1 for statistical details.
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