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A and B: Stable isotope bi-plots for the 20 study lakes, with δ15N on the Y-axis and δ13C on the X-axis. Lakes are sorted by salinity (see Table 1), increasing within rows from row 1 to row 10. Data are averaged over the four sampling dates (June 2007, August 2007, June 2008, August 2008). Fish taxa are indicated by crosses (+), zooplankton by squares (□), and littoral invertebrate by triangles (Δ). Zooplankton is further separated into cladocerans (black squares, ■), copepods (open squares, □), invertebrate predators (i.e., Leptodora or Chaoborus; dark grey squares, ■) and other macroinvertebrates (e.g., corixids; light grey squares, ■). Within littoral invertebrates, amphipods are indicated by black triangles (▲).