The distribution of four Chaoborus species (Diptera: Chaoboridae) along an elevation gradient in Canadian Rocky Mountain lakes

Abstract

We tested the hypothesis that the distribution of four species of Chaoborus is limited by water temperature in Rocky Mountain lakes. Midsummer surface water temperature (MSSWT) of Rocky Mountain lakes varied between 25 and 5 °C along an elevation gradient spanning 600–2400 m above sea level. Chaoborus (subgenus Chaoborus) americanus and C. (C.) flavicans were collected in lakes with MSSWT ≥ 16 °C, generally corresponding to lakes at elevations lower than 1600 m above sea level. Chaoborus (Sayomyia) punctipennis was only collected in warm lakes (MSSWT ≥ 21 °C). Species of the subgenus Schadonophasma (C. trivittatus and possibly C. cooki) were not commonly collected, but preliminary data suggest that they may be more tolerant of low water temperatures than the other species. On a qualitative basis, the distribution of these chaoborids in the Rockies is similar to their latitudinal distribution. However, MSSWT as a valid predictor of Chaoborus species distribution with latitude remains to be tested. The gradient in lake temperature found in mountainous environments appears to be a useful gauge for obtaining information about the distribution of invertebrates relative to temperature.