Methodological Detail from David Lewis' Ph.D. Dissertation and Lewis and Magnuson (2000)

We surveyed each lake once for snails and several variables that potentially influence snail distribution. Prior to sampling, lake habitat was determined by mapping around the entire shoreline of a lake at 30 m intervals or by consulting habitat maps (Petrie et al. 1993) that we confirmed for accuracy. Sample sites were chosen randomly, stratifying by habitat type.

During the summer of 2006, we collected snails at 4 to 6 sites in each of 44 focal lakes. Survey lakes ranged in surface area from 14 to 1400 ha (median = 130 ha), and were selected to span broad gradients of landscape position, water chemistry, human use, and other characteristics, and to maximize overlap with lakes where Morrison (1932) has previously described snail assemblages (see below).