Diversity of deep-water cetaceans and primary productivity

Recently, it has been suggested that mammal diversity both on land and in the sea is controlled by patterns of primary productivity. Here we tested the hypotheses that large-scale patterns of marine mammal diversity are linked to primary productivity, sea surface temperature (SST) or a combination of these 2 factors. We used a consistently sampled sightings database of deep-water cetaceans in the Atlantic and Pacific Oceans, along with in situ SST measurements and 3 satellite-derived productivity measures matched spatially and temporally to available sightings. Cetacean genus richness peaked in regions of high primary productivity (>1000 to 1500 mg C m^-2 d ^-1), but most of this effect is captured by optimal SST in those same regions. Our results show that the best-supported, explanatory models of cetacean diversity included SST, while the addition of satellitederived measures of productivity did not improve predictive capacity. Marine mammal richness globally peaks around 40°N and S, and may result more directly from optimal SST at these latitudes rather than high oceanic productivity.