PARENT SESSION
Oral Session #30: Landscape Ecology: Dynamics and patterns. Presiding: A. Hansen.
Tuesday, August 7, 2001. 1:00 PM to 5:00 PM. Madison Ballroom D.

Species richness and geographic range boundaries of benthic marine algae of the Pacific coast of North America.

Sax, Dov¹, Gaines, Steven¹, Thornber, Carol¹, ¹

ABSTRACT- Examining patterns of species distributions at biogeographic scales are critical to understanding the ultimate mechanisms that limit species distributions and abundance. To facilitate this we have compiled a database of species distributions of benthic marine algae from the Pacific coast of North America, from Cook Inlet, Alaska, to San Diego, California. Within this region species richness increases with decreasing latitude. In addition to this latitudinal gradient, there are also several extra-gradient peaks in richness. These peaks are coincident with regions of high species turnover. These regions contain more species range boundaries than are expected by chance and can therefore be considered to be biogeographic boundaries. These boundaries are bi-directional and are the limit of both northern most and southern most species distributions. They occur at 33, 34, 36 and 48 degrees of latitude. Within California, intertidal invertebrate distributions show coincident boundaries with algae at 34 and 36, but not at 33 degrees. Boundaries that are consistent across taxa suggest regions where more focused field experimentations could be done to elucidate the causal mechanisms for these patterns.

KEY WORDS: benthic marine algae, diversity, species richness, biogeographic boundaries