PARENT SESSION
Symposium 22: Expanding Scales, Expanding Perspectives: New Insights into Marine Ecosystem Dynamics
Organized by: P Raimondi and B Menge
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Oglethorpe Auditorium.

Latitudinal diversity gradients: Percolating up from small scales.

Russell, R¹, Allison, Gary^{*,2, 101}, Menge, Bruce¹, ¹ Oregon State University, Corvallis, OR² Department of Evolution, Ecology, and Organismal Biology, Columbus, OH¹⁰¹

ABSTRACT- Latitudinal gradients in diversity have provided important patterns for ecological debate. Such patterns are often estimated from species ranges or other indirect means. Because patterns span such large areas, they are rarely verified with on-the-ground measurements. Because of this lack of verification, the reliability of macroecological datasets and their usefulness in both quantifying pattern and evaluating mechanisms can be uncertain. We have begun to address this and related issues by establishing an extensive and intensive monitoring program of rocky intertidal community structure. Here we use this dataset to evaluate a purported gradient of macroalgal diversity across the west coast of the continental US. This survey quantifies abundance of 250 taxa in 5000 quadrats annually. Sampling is spatially nested and includes both biotic and physical measurements to help determine the primary physical predictors of community structure. Across this large area, the direction of the gradient we find in macroalgal diversity contradicts what was expected based on range data: higher diversity is found at higher latitudes. Among the primary explanations for this unexpected diversity pattern are, with increasing latitude: increasing tidal excursion, increasing wave force (both potential proxies of or influence on total habitat area), decreasing temperature, and increasing nutrient availability. Although many of the potential factors co-vary across the survey, we matched scales of variation in diversity with the variation in these factors to help us identify the best predictors. Preliminary analyses suggest that area is a major determinant of the diversity pattern. Although funding agencies avoid supporting "monitoring" programs, our results suggest that such programs are critical for the development of rigorous databases that will be useful in accurately quantifying macroecological patterns, and for pointing the way towards evaluation of likely mechanisms.

Key words: rocky intertidal, latitudinal gradient of diversity, macroalgae, species-area