Evolution of the grazing niche in Pleistocene mammals from Florida: evidence from stable isotopes

Previous isotopic studies of herbivorous mammals suggested that the dispersal of the grazing mammals, Mammuthus and Bison resulted in the endemic grazers incorporating more browse into their diets. In order to test this hypothesis, we analyzed 84 bulk enamel samples from six co-occurring genera from the Pleistocene of Florida to determine their carbon isotopic composition, We also analyzed 145 samples taken from along the growth axis of the tooth (serial sampling) from 12 specimens of three co-occurring genera in order to investigate seasonal resource partitioning. Our results suggest that: 1. There were no inter-generic or intra-generic differences in feeding strategy for Equus, Bison, and Mammuthus throughout the Pleistocene of Florida. 2. Significant isotopic differences observed in the feeding strategy of Hemiauchenia and Platygonus are due to floral shifts or to interactions with other grazers in Florida. 3. The three late Pleistocene sympatric grazers displayed similar seasonal carbon isotopic variations, suggesting either the lack of forage specificity or abundant resources making forage partitioning unneccessary. 4. Because these organisms did coexist, niche partitioning must have occurred by some aspect not discernible through analyzing stable carbon and oxygen isotopes. Stable isotopic analysis of herbivore tooth enamel allows for the quantitative understanding of specific paleoecological interactions among ancient animals. Further analysis of seasonal-scale changes of ancient ecosystems will bring us closer to the scale of understanding seen in present-day ecosystems. (C) 2000 Elsevier Science B.V. All rights reserved.