NORTH AMERICAN PREDATOR FUNCTIONAL DIVERSITY AND NOVEL NICHE EXPLORATION AFTER THE EOCENE

The North American landscape of mammalian carnivores has shifted over the last 40 million years as prey resources have changed and genera have come and gone. In order to maximize energetic usage and reduce competition, we would expect co-occurring taxa to divide up the total functional niche space available into different functional categories, while accounting for shifts in the environment and diversity of taxa. This broad diversification into different functional categories should occur fairly quickly as taxa move into available functional niches to reduce competition, after which we expect a period of stability in functional richness and further sub-stratification and specialization within functional categories. To test this, we assembled a dataset consisting of body mass calculated from m1 length and relative blade length (RBL) of the largest lower molar (carnassial) for 339 North American predator species from the Oligocene to the present. To quantify predator niche exploration, we assigned each species into two functional categories: body mass and diet. We mapped the occupancy of these functional groups across each of the North American land mammal ages from the Orellan through the Holocene. Using functional diversity metrics, we found discordance between predator diversity and functional richness or evenness, where periods of maximum taxonomic diversity exhibit low functional richness and evenness. We also uncovered a prolonged initial period of low functional richness, indicating a potential lag between taxonomic and functional diversification in North American over tens of millions of years. Functional richness and evenness of North American predators peak in the Pliocene, despite a major loss of taxa, in contrast with the low functional evenness of the depauperate North American carnivore fauna today. Contrary to our predictions, North American predators took much of the last 30 million years to accumulate maximal functional richness. Moreover, it appears that uneven or skewed distributions of species among functional groups may be stable and persist despite expectations of niche partitioning.