Stable Isotope Ecology of Extant Tapirs from the Americas

Understanding the ecology of modern and ancient forests can help clarify the evolution of forest dwelling mammals. It is first necessary, however, to elucidate the source and extent of stable isotope variation in forest taxa. Tapirs are of particular interest because they are model organisms for identifying forest environments due to their highly conservative diet and habitat preferences. Here, stable carbon and oxygen isotopic compositions of extant tapirs are quantified to test hypotheses regarding ontogenetic diet shifts, stable isotope variation at the population level, and relationships between stable isotopes and climatic variables. A population of extant tapirs (Tapirus bairdii) demonstrates low delta C-13 variation (similar to 2-3%) and increased delta C-13 values in late erupting teeth, indicating that juveniles consume C-13 deplete milk and/or browse in denser forests. Disparate delta O-18 values of late erupting teeth are instead reflecting seasonal variation. Extant tapir (T. bairdii, Tapirus pinchaque, Tapirus terrestris) delta O-18 values are constrained by climatic and geographic variables. Most notably, delta O-18 values of T. bairdii decrease with decreasing precipitation frequency. Tapirus terrestris is typically present in areas with greater precipitation than T. bairdii and delta O-18 values instead positively correlate with delta C-13 values. These data indicate that tapirs in wetter areas are getting a larger proportion of their water from leaves experiencing less evaporation in denser canopies, while T. bairdii is interpreted to increase its consumption of water via drinking when present in drier areas. An understanding of extant tapir stable isotope ecology improves ecological interpretations of these elusive mammals both today and in the past.