Zooplankton community composition of lakes in the Yukon and Northwest Territories (Canada): relationship to physical and chemical limnology

We analysed associations between zooplankton species composition and local abiotic factors in 30 lakes located along a 900 km south-north transect fro m Whitehorse (Yukon Territory) to Inuvik (Northwest Territories). The lakes were situated in three broadly defined vegetation zones: (i) Boreal forest (between Whitehorse and Dawson City), (ii) alpine tundra (Ogilvie mountain s north of Dawson City) and (iii) subarctic forest-tundra (near Inuvik). La kes in the alpine tundra were characterised by lower conductivity, temperat ure, chlorophyll a and nutrients than those in the other two zones. Those i n the forest-tundra were generally small and shallow, and had higher chloro phyll a concentrations than lakes further south. Lakes in forested catchmen ts spanned a larger latitudinal range and exhibited a greater variety of ph ysical and chemical characteristics. However, they were generally deeper, w ith higher conductivity, temperature and ionic concentrations. Forty-one zo oplankton taxa were identified from the 30 lakes, of which the most frequen tly occurring were the rotifers Conochilus unicornis, Kellicottia longispin a, Keratella cochlearis and Polyarthra vulgaris, the cladocerans Daphnia mi ddendorffiana and Bosmina longirostris, and the copepods Leptodiaptomus pri bilofensis, Heterocope septentrionalis and Cyclops spp. The lakes contained between two and fifteen species (mean = 6.9). Alpine tundra lakes containe d slightly less species (mean = 5.8) than those at lower elevations; in par ticular the cladoceran fauna was depauperate or absent. Relationships among the lakes, species and environmental factors were examined using canonical correspondence analysis, with forward selection and associated Monte Carlo permutation tests. Chloride, silica and temperature showed statistically s ignificant relationships with species distribution, and together these abio tic factors explained 25% of the variation in zooplankton communities withi n Yukon and Northwest Territories lakes.