34.3 Thursday, Jan. 5 Do clams of a feather arise together? Evolutionary dynamics, latitudinal gradients, and the global deployment of bivalve life habits BERKE, Sarah K*; JABLONSKI, David; KRUG, Andrew Z.; University of Chicago; University of Chicago; University of Chicago email@example.com
Functional diversity (i.e. the variety of life habits) is a critical component of overall biodiversity, with important implications for ecosystem function and the nature of adaptive radiations. Here we investigate the macroecological patterns in functional diversity for marine bivalves worldwide, using a database of occurrences for >5,000 species worldwide. We define functional groups by trophic mode, exposure on the seafloor, locomotory mode, and body size, using counts of trait combinations as well as distance-based metrics to assess latitudinal trends in functional diversity. Unsurprisingly, functional richness is a saturating function of taxon richness. However, we find an inverse latitudinal diversity gradient (LDG) for functional evenness (the distribution of taxa in niche space), even when taxon richness is controlled for. Thus, clustering in functional space increases at lower latitudes. This trend is likely driven by different origination rates among functional groups, working in concert with an LDG in origination rates. Younger genera, reflecting high origination rates, are disproportionately represented in the tropics. Functional groups with a greater proportion of young genera consequently come to represent a larger fraction of low-latitude faunas, increasing the uneven distribution of taxa among functional groups there. Surprisingly, originations do not show a recent downturn, and thus provide no evidence of saturation in any functional traits, despite the fact that the area of tropical habitats has shrunk over the past 5 my. Crowding of taxa into spatial bins and functional categories has evidently not impeded continued diversification for the most prolific bivalve clades and modes of life.