Stable isotope canopy effects for sympatric monkeys at Taï Forest, Côte d'Ivoire

This study tests the hypothesis that vertical habitat preferences of different monkey species inhabiting closed canopy rainforest are reflected in oxygen isotopes. We sampled bone from seven sympatric cercopithecid species in the Taï forest, Côte d'Ivoire, where long-term study has established taxon-specific patterns of habitat use and diet. Modern rib samples (n = 34) were examined for oxygen (δ18Oap) and carbon (δ13Cap) from bone apatite (‘bioapatite’), and carbon (δ13Cco) and nitrogen (δ15Nco) from bone collagen. Results are consistent for C3 feeders in a closed canopy habitat. Low irradiance and evapotranspiration, coupled with high relative humidity and recycled CO2 in forest understory, contribute to observed isotopic variability. Both δ13Cco and δ13Cap results reflect diet; however, δ13C values are not correlated with species preference for canopy height. By contrast, δ18Oap results are correlated with mean observed height and show significant vertical partitioning between taxa feeding at ground, lower and upper canopy levels. This oxygen isotope canopy effect has important palaeobiological implications for reconstructing vertical partitioning among sympatric primates and other species in tropical forests.