Food mechanical properties and isotopic signatures in forest versus savannah dwelling eastern chimpanzees

Adam Van Casteren,Fiona A Stewart,Mohamed Kambi,Christophe Boesch,Samuel Angedakin,Hjalmar S Kühl,Kornelius Kupczik,Ammie K Kalan,Vicky M Oelze,Kevin E Langergraber,Alexander K Piel

doi:10.1038/s42003-018-0115-6

Abstract

Chimpanzees are traditionally described as ripe fruit specialists with large incisors but relatively small postcanine teeth, adhering to a somewhat narrow dietary niche. Field observations and isotopic analyses suggest that environmental conditions greatly affect habitat resource utilisation by chimpanzee populations. Here we combine measures of dietary mechanics with stable isotope signatures from eastern chimpanzees living in tropical forest (Ngogo, Uganda) and savannah woodland (Issa Valley, Tanzania). We show that foods at Issa can present a considerable mechanical challenge, most saliently in the external tissues of savannah woodland plants compared to their tropical forest equivalents. This pattern is concurrent with different isotopic signatures between sites. These findings demonstrate that chimpanzee foods in some habitats are mechanically more demanding than previously thought, elucidating the broader evolutionary constraints acting on chimpanzee dental morphology. Similarly, these data can help clarify the dietary mechanical landscape of extinct hominins often overlooked by broad C3/C4 isotopic categories.

Highlights

Chimpanzees are traditionally described as ripe fruit specialists with large incisors but relatively small postcanine teeth, adhering to a somewhat narrow dietary niche
Data on the mechanical properties effectively hail from one tropical forest[18], and it is doubtful these values accurately reflect the dietary variance of the species
Continued isotopic research has indicated that across chimpanzee habitats, from rainforest to savannah, the values of δ13C and δ15N vary significantly[21,22]. These patterns are thought to occur because savannah chimpanzees rely more on plant foods produced under drier environments with reduced canopy cover compared to those of their forest counterparts. It remains unclear if utilising foods from different environments affects food material properties in different chimpanzee populations and how this is related to isotopic signatures

Summary

Introduction

Chimpanzees are traditionally described as ripe fruit specialists with large incisors but relatively small postcanine teeth, adhering to a somewhat narrow dietary niche. These patterns are thought to occur because savannah chimpanzees rely more on plant foods produced under drier environments with reduced canopy cover compared to those of their forest counterparts It remains unclear if utilising foods from different environments affects food material properties in different chimpanzee populations and how this is related to isotopic signatures. The instigation of this adaptive morphology predates the incorporation of large amounts of C4 resources into the hominin diet[11,24,30,31,32] This may indicate that the dietary mechanical pressures that predisposed early hominins to increased craniodental robusticity are to be found in C3 as well as C4 food resources of the mosaic woodland environment

Methods

Results

Conclusion