Field tests of interspecific resource-based competition among phytoplankton.

The hypothesis that interspecific resource-based competition caused the spring and summer vertical segregation of phytoplankton species was tested in Lake Tahoe (California/Nevada). Two species (Cyclotella glomerata Bachmann and Synedra radians Kütz.) became dominant at different depth intervals (0-30 m and 60-90 m, respectively). Experimental transplants of assemblages between depths demonstrated asymmetrical competition. In the phosphate-limited region near the surface, growth of S. radians declined in the presence of C. glomerata. However, growth of C. glomerata was not affected by the presence of S. radians in the light-limited region at depth. This study provides field verification of resource-based competition theory.