Landscape spatial patterns in freshwater snail assemblages across NorthernHighland catchments

1. Limnologists and landscape ecologists have illustrated how the spatial p osition of a lake in a landscape influences many of its properties, from th e physical to the social. Taking a community ecology perspective, we invest igated whether freshwater gastropod assemblages respond to lake landscape p osition. 2. We determined: (a) whether there is any spatial pattern among lakes in e ither the species richness or composition of gastropod assemblages; (b) the form of any spatial pattern; and (c) if any explanatory variables (e.g. di spersal corridors and limiting local conditions) show a similar pattern. 3. In three different hydrological catchments, snail species richness incre ased from isolated highland lakes to stream-connected lowland lakes, probab ly reflecting increased colonization potential and less limiting local fact ors for lowland drainage lakes. Catchments appear to differ from one anothe r with regard to relative species abundance, both in terms of macrophyte-as sociated snail fauna and snails from all habitats aggregated. One or more h istorical events, such as chance dispersal, may have produced this pattern. Taken together, these results suggest that within-catchment constraints pr oduce repeated gradients in species richness, regardless of what species co mposition persists in the catchment.