PARENT SESSION
Oral Session # 5: Biogeography I: Community Structure and Diversity.
Presiding: B Enquist
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 104.
Assembly of woody plant communities: Patterns of functional trait diversity.
Cornwell, William*,1, Ackerly, David*,1, 1 Dept. of Biological Sciences, Stanford, CA, USA
ABSTRACT- The controls on functional diversity of communities are crucial to ecosystem function and have received relatively little attention. The persistence of a species at a site is determined by the species' functional traits, the abiotic conditions, and species interactions. If a trait is strongly associated with habitat tolerance, only species that possess a narrow range of that trait value can establish and persist. Alternatively, if a trait is associated with resources that are being divided among species—a niche axis—species with similar values of that trait will be excluded and the spread of trait values will be large. Here, we quantify the functional diversity of communities using the variance in functional trait values of species. We present a study of woody plant communities across a topographically-mediated gradient in water availability in coastal California. We measured leaf and xylem functional traits for every woody species that occurred at our sites (including measures of intraspecific variation across sites for widespread species). We then constructed a null model in which we selected species randomly from the pool of species in the study. The variance of the observed distribution of functional trait values, relative to the null model, provides a test for non-random assembly processes. Overall, the observed variances of leaf and xylem traits were significantly lower than in the null model, suggesting a dominant role of habitat tolerance. However, there were contrasting trends in trait variance across the abiotic gradient. At the dry end of the gradient, variance of wood density decreased and variance of leaf size increased suggesting inverse shifts in the relative importance of habitat and niche partitioning for each trait. Future work will incorporate multivariate models examining shifts in the distributions of trait combinations associated with different plant strategies.
Key words: functional diversity, niche, plant functional traits, null model