Notes on the distribution of the mayfly Caudatella edmundsi (Allen, 1959) (Ephemeroptera: Ephemerellidae)

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During the summers of 1988 and 1989 the authors made extensive collections of benthic invertebrates from 45 streams located throughout the Sierra Nevada, the Klamath Mountains, and the North Coast Range of California. They also quantified the physical and biological environments at these sites. Larvae of Caudatella edmundsi were found in in 4 of these streams draining the western slope of the central and southern Sierra Nevada. Observations indicate that streams with C. edmundsi were deeper, steeper, lower in substrate diversity, and higher in cascade habitats than streams without this species. Caudatella edmundsi larvae were also more likely to be collected from streams sampled early in the summer than those sampled later. Streams with this mayfly also tended to have lower mean summer temperature, higher amounts of moss, and occurred at higher elevation. Furthermore, C. edmundsi larvae appear to be restricted to the aquatic moss Fontinalis Hedwig (Fontinalaceae). Inspection of all other known collection records indicates that, as in most western North American mayfly species, C. edmundsi occurs at progressively lower elevations with increasing proximity to the Pacific coast, but there is no apparent relationship between elevation and latitude. Furthermore, the distribution of this species now best matches the Northwest and Coast Ranges Distribution Pattern of the Western North American Subdivision of mayfly distributions that is comprised of the mountainous regions of northern Baja California, California, Oregon, Washington, Idaho, western Montana and Wyoming, and southern British Columbia and Alberta. The authors suspect this mayfly will be found in other high-gradient, cold, mountainous streams throughout this region in microhabitats dominated by aquatic moss.

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ELECTRONIC FILE - Zoology: Invertebrates