Environmental Profile of Tricorythodes minutus Traver (Ephemeroptera: Tricorythidae) in the Western United States

ABSTRACT

Based on data from 892 stations in 11 western states two geographic populations of Tricorythodes minutus Traver are described. The Great Basin population was found in streams that had sedimented substrate, sparse riparian vegetation, low channel gradients, and moderate to high concentrations of alkalinity and sulfates. The other population, found in California and Oregon, commonly occupied streams with moderate siltation, dense riparian vegetation, and low alkalinity and sulfate concentrations. The differences between the two populations could be the result of competitor or predator avoidance by one or both populations, or different limiting seasonal or irregular events may cause the separation. It is possible that the two populations represent subspecies or even two distinct species.