title: Food mechanical properties, feeding ecology, and the mandibular morphology of wild orangutans.
abstract: Bornean orangutan mandibular morphology has been functionally linked to the exploitation of hard and tough foods, based on evidence that Pongo pygmaeus wurmbii spends a greater percentage of time feeding on bark, seeds and vegetation compared with Pongo abelii (Sumatran orangutans) and the assumption that these tissues are more challenging to process than fruit pulp. We measured and compared toughness (R) and Young's modulus (E) of ripe and unripe foods exploited by P. abelii and P. p. wurmbii. Additionally, we recorded and compared the percentage of time these orangutans fed on plants/plant parts of varying degrees of R and E. Compared with P. abelii, P. p. wurmbii consumed significantly tougher and more displacement limited (R/E)(0.5) fruit parts, leaves and inner bark, and spent a significantly greater percentage of time feeding on immature leaves, unripe fruit and other vegetation. Modulus did not vary as expected between species, likely because we failed to capture the high-end range of modulus values for tissues consumed by P. p. wurmbii. Notably, P. p. wurmbii spent ∼40% of its feeding time on the toughest foods consumed (between 1000 and 4000 J m(-2)). Thus, the hypothesis that mandibular robusticity in P. p. wurmbii is functionally linked to feeding on tough foods is supported and is likely related to countering relatively larger external forces and/or repetitive loads required to process the toughest tissues. The importance of elastic modulus on morphological divergence awaits future studies capturing the full range of this material property for P. p. wurmbii. Finally, phenophase and fruit availability influence orangutan species differences in food material properties and percentage of time spent feeding on various foods, emphasizing the importance of incorporating these variables in future studies of feeding ecology and craniodental morphology in extant taxa.
authors.affiliation: Department of Anthropology and Center for Human Evolutionary Studies, Rutgers, The State University of New Jersey, 131 George Street, Ruth Adams Building Suite 306, New Brunswick, NJ 08901-1414, USA. Electronic address: erin.vogel@rutgers.edu.
authors.forename: Erin R
authors.initials: ER
authors.lastname: Vogel
authors.affiliation: Universitas Nasional Jakarta, Jakarta, Indonesia.
authors.forename: Astri
authors.initials: A
authors.lastname: Zulfa
authors.affiliation: Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Madeleine
authors.initials: M
authors.lastname: Hardus
authors.affiliation: School of Natural Sciences and Psychology, Liverpool John Moores University, Liverpool, UK.
authors.forename: Serge A
authors.initials: SA
authors.lastname: Wich
authors.affiliation: Department of Anthropology, 6047 Silsby Hall, Dartmouth College, Hanover, NH, USA.
authors.forename: Nathaniel J
authors.initials: NJ
authors.lastname: Dominy
authors.affiliation: Department of Community and Family Medicine, Duke University School of Medicine, Box 104002, Durham, NC 27708, USA; Department of Evolutionary Anthropology, Duke University, 104 Biological Sciences Building, Box 90383, Durham, NC 27708-9976, USA.
authors.forename: Andrea B
authors.initials: AB
authors.lastname: Taylor
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001696:Biomechanical Phenomena; D055119:Elastic Modulus; D005247:Feeding Behavior / Q000502:physiology*; D005260:Female; D005638:Fruit / Q000502:physiology; D008334:Mandible / Q000502:physiology*; D057079:Pongo / Q000502:physiology*
keywords: Diet; Feeding behavior; Mandibular morphology; Pongo; Toughness; Young's modulus