Distribution of Waterfowl Broods in Sudbury Area Lakes in Relation to Fish, Macroinvertebrates, and Water Chemistry

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Abstract
We studied habitat selection by insectivorous waterfowl in 65 small lakes near Sudbury, Ontario. Data on environmental variables (pH, alkalinity, conductivity, calcium, total phosphorus, dissolved organic carbon (DOC), and area), fish, and littoral macroinvertebrates indicated that the distribution of broods was influenced by differences in invertebrate prey assemblages in lakes with differing degrees of acid stress and types offish predation. Lakes ranged in pH from 4.2 to 7.7 (mean = 5.8); 40% were fishless, 43% were dominated by yellow perch (Perca flavescens) or white sucker (Catostomus commersoni) (YP/WS), and the remainder contained only small cyprinids, sticklebacks, or darters (C/S). Fishless lakes were more acid than lakes with fish. Compared with fishless lakes, C/S lakes had higher levels of DOC and YP/WS lakes were larger. Macroinvertebrate composition was strongly related to fish composition and suggested increasing predation along a gradient: fishless < C/S < YP/WS. pH-related variables distinguished lakes with a taxonomically rich benthos from those with a taxonomically poorer fauna. Insectivorous waterfowl selected fishless lakes over lakes with fish and C/S over YP/WS lakes. Lakes with species-rich, acid-sensitive invertebrate assemblages were not selected over those typified by species-poor, acid-tolerant ones.