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Notes on the Food Habits of the Salamanders of Crater Lake, Oregon

1947; American Society of Ichthyologists and Herpetologists; Volume: 1947; Issue: 4 Linguagem: Inglês

10.2307/1438923

1938-5110

Donald S. Farner,

Insect and Arachnid Ecology and Behavior

C RATER Lake is situated in the caldera of an extinct Pleistocene Volcano, Mount Mazama, of the high Cascade Mountains in southern Oregon. The surface of the lake is 6,177 feet above sea level; the surface area is approximately 21 square miles, and the maximum depth is slightly less than 2,000 feet. In most places at the edge of the lake sheer cliffs or steep talus slopes rise to between 500 and 2,000 feet above the surface. Much of the shoreline consists of irregular wave-washed fragments of andesite, dacite, and to a lesser extent other lava fragments varying in size from a few inches to several feet in diameter. Beneath these fragments, where there is dampness due to wave action, are found the adults of the two species of Crater Lake salamanders, Ambystoma macrodactylum Baird and Triturus granulosus mazamae Myers. The subspecies mazamae is, insofar as now known, endemic to Crater Lake. The adults of the two species occur in approximately equal numbers and apparently in precisely the same daytime habitat since I have found many times individuals of both species under the same rocks. In August, 1946, I collected 56 salamanders for purposes of stomach examinations. Of these, 27 were Ambystoma macrodactylum and 29 were Triturus granulosus mazamae. The identifications were made by Dr. Edward H. Taylor, Museum of Natural History, University of Kansas, in which museum specimens have been deposited. Specimens of both species were almost invariably taken from beneath the same rocks. Of the 27 stomachs from Ambystoma macrodactylum, 19 contained food material. Fourteen of these (74 per cent) contained terrestrial arthropods, almost always in fragments. These were mostly pieces of ants, beetles, and flies. Around and beneath the rocks under which the salamanders were taken I found many fragments of these terrestrial arthropods; entire individuals were rarely found. The stomachs of Triturus granulosus mazamae contain whole individuals of fresh-water amphipods, aquatic arthropods of more delicate nature than the above-mentioned terrestrial arthropods. These fresh-water amphipods are available alive and presumably are taken alive by mazamae. Because of the almost constantly fragmentary nature of the terrestrial arthropods found both in the stomachs and the environment of macrodactylum, and because the more delicate amphipods occur as entire individuals in the stomachs of mazamae, I infer that macrodactylum obtains terrestrial arthropods primarily as fragments by scavenging. Seven stomachs (37 per cent) of Ambystoma macrodactylum contained the larvae of coleopterous, dipterous, and trichopterous aquatic insects, two stomachs held unidentifiable material and one only a fragment of andesite about one centimeter in length. Of the 29 stomachs of Triturus granulosus mazamae examined, there