Bear Lake, Utah and Idaho, is one of only a few lakes worldwide with endemic ostracode species. In most lakes, ostracode species distributions vary systematically with depth, but in Bear Lake, there is a distinct boundary in the abundances of cosmopolitan and endemic valves in surface sediments at ~7 m water depth. This boundary seems to coincide with the depth distribution of endemic fish, indicating a biological rather than environmental control on ostracode species distributions. The cosmopolitan versus endemic ostracode species distribution persisted through time in Bear Lake and in a neighboring wetland.

The endemic ostracode fauna in Bear Lake...