Which types of species tend to dominate river ecosystems? how do conditions between fast-moving 'headwaters' (or sources) of rivers differ from slow-moving 'mouths' of rivers? where are the majority of producers in a lake located? where would you expect to find the largest food webs - oligotrophic, mesotrophic, or eutrophic lakes? explain. what characteristic defines a wetlands? why are wetlands so ecologically productive, and what valuable ecosystem services do they provide to humans? where are coral reefs generally found, how are they built, and why are they under heavy threat from bleaching? do the vast open oceans areas deeper than ~200 meters and away from coastlines support much life? explain