SPECIES RICHNESS, ENDEMISM AND ECOLOGY OF CRUSTACEAN ASSEMBLAGES IN NORTHERN CALIFORNIA VERNAL POOLS

Ephemeral pools occur worldwide, provide habitat for organisms with a variety of life history strategies, and may have served as evolutionar y refugia for some taxa since Mesozoic times. Yet, our understanding o f the ecology and evolutionary history of ephemeral pool communities i s hampered by a paucity of such basic data as the species composition of pool assemblages. We surveyed 58 vernal (ephemeral spring-time) poo ls from 14 sites in northern California for crustaceans, and found div erse assemblages composed largely of endemic and rare species. Sixty-s even species of crustaceans were found, and as many as 30 of these may be new, undescribed species. Differences in species composition among pools correspond with physical and chemical aspects of the habitat (d epth, solutes concentration, elevation, biogeographic region), and wit h existing geologic/floristic-based habitat descriptions. Species rich ness is positively correlated with both depth and surface area. This r elationship can be explained in terms of hydroperiod (accommodation of species with slower developmental rates in long-lived pools, greater time for temporal resource partitioning) and size (spatial habitat het erogeneity). High species richness and numerous co-occurrences of cong eneric species in temporary pools may be due to super-abundant resourc es, low levels of predation, and annual truncation of the community wh ich prevents ecological interactions from going to completion. The res ults of this survey underscore the need for conservation of the vernal pool habitat and endemic vernal pool species in California. The best preservation strategy will include many pools at each site, multiple s ites of each habitat type, and all identified habitat types.