We examined stomach contents of preserved specimens of larval Pacific giant salamander (Dicamptodon tenebrosus) and Cope's giant salamander (D. copei) collected from sympatric and allopatric stream populations. The dietary components of these specimens were used to calculate dietary overlap between the 2 species and to determine if changes in overlap existed between sympatric and allopatric populations. To statistically test overlap values, a randomization algorithm was used to construct a simulated data matrix (i.e., null model) in order to compare observed values of dietary overlap to a distribution of overlap values from the null model. Significant levels (P < 0.05) of dietary overlap occurred in all cases of sympatry as well as allopatry. Average dietary overlap in sympatry was significantly lower than in allopatry, suggesting a dietary shift when in sympatry to reduce competition. Diet composition also differed between sympatric and allopatric populations of each species, further suggesting a partitioning of food resources by one or both species when in the presence of its congener.
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Vol. 66 • No. 1