Fig. 1From: Ongoing niche differentiation under high gene flow in a polymorphic brackish water threespine stickleback (Gasterosteus aculeatus) populationGeographical location of the brackish water Lake Engervann; a) location in Norway, b) location within the marine Oslofjord Fjord, and c) location within the Sandvikselva River drainage. In c) the upper (* close to the River Øverlandselva; freshwater influenced) and the lower (* close to the outlet river; saltwater influenced) sampling sites are given. Symbol * denotes also sampling stations of stable isotopes from putative prey items. Number 1–4 refers to the two replicate sampling sites for a benthic invertebrate survey by Halvorsen et al. [33] (data modified by us and presented in Additional file 8: Table S5). Salinity is illustrated as colors; dark grey = salt water, light grey = brackish-salt water and light grey = brackish-freshwaterBack to article page