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 implies a complex ecosystem that evolved in a hydrologically stable, but not invariant, environmental setting that was long lived. Long-lived (geologic time scale) hydrologic stability implies the lake persisted for hundreds of thousands of years despite climate variability that likely involved times when effective moisture and lake levels were lower than today. The hydrologic budget of the lake is dominated by snowpack meltwater, as it likely was during past climates. The fractured and karstic bedrock in the Bear Lake catchment sustains local stream flow through the dry summer and sustains stream and ground-water flow to the lake during dry years, buffering the lake hydrology from climate variability and providing a stable environment for the evolution of endemic species.