Influences of natural acidity and introduced fish on faunal assemblages inCalifornia alpine lakes

In an alpine area of the Sierra Nevada of California, naturally acidic wate rs and introduced fishes both strongly affect the distributions of native a mphibians, zooplankton, and macroinvertebrates. The study area in Kings Can yon National Park contains 104 lakes with pH values between 5.0 and 9.3, in cluding 10 lakes with pH < 6.0 (defined here as acidic lakes) and 18 lakes with introduced trout. We surveyed 33 of these lakes (8 acidic, 7 non-acidi c with trout, 18 non-acidic without trout) for water chemistry and faunal a ssemblages. Yellow-legged frog tadpoles (Rana muscosa), common microcrustac eans (Daphnia, Hesperodiaptomus, Diaptomus), and larvae of a caddisfly (Hes perophylax) were rare or absent in acidic lakes but common in non-acidic la kes, and microcrustacean and macroinvertebrate species richness decreased w ith decreasing pH. Large and (or) mobile, conspicuous taxa, including tadpo les, large-bodied microcrustaceans (Hesperodiaptomus, Daphnia middendorffia na), and many epibenthic or limnetic macroinvertebrates (baetid and siphlon urid mayfly nymphs, notonectids, corixids, limnephilid caddis larvae, and d ytiscid beetles), were rare or absent in trout lakes but were relatively co mmon in lakes lacking trout, and the taxon richness of macroinvertebrates w as reduced by trout.