Wright BW, Ulibarri L, O'Brien J, Sadler B, Prodham R, Covert HH, Nadler T. 2008. It's tough out ... Paul Opere and John Ndege for their help in behavioral data ...
Leaf fracture toughness and foraging efficiency in Angola black and white colobus monkeys from the Diani Forest of Kenya Noah Dunham 1 and Alexander Lambert 2 1Department of Anthropology, The Ohio State University; 2 Independent
Introduction
Methods
• Behavioral ecologists and functional morphologists are increasingly interested in relationships between food mechanical properties and oral processing behaviors for insight into masticatory morphology. 1, 2 • While investigations of dietary toughness typically focus on explaining behavioral and morphological differences between primate taxa, considerably less attention has been given to examining how food items of varying toughness influence foraging efficiency within a taxon. 3, 4 • The purpose of this study was to assess the relationships among leaf toughness, ingestion rate, and mastication by a highly folivorous African colobine monkey. • We hypothesize that foraging efficiency will decrease as toughness values increase such that leaf toughness will: 1) negatively correlate with ingestion rate (g/min) 2) positively correlate with masticatory frequency (chews/g) 3) positively correlate with masticatory rate (chews/min).
Behavioral Measures • Data on adults from three groups Colobus angolensis palliatus from the Diani Forest of Kenya from July 2014 – December 2015. • Ingestion rates: Calculated by counting number of food items ingested x the mass of a given item during 3-5 minute focal periods. 5 • Masticatory frequency (chews/g) and masticatory rate (chews/ min): Number of mastications counted during 3-5 minute focal periods. Toughness Measures • Toughness measured on young leaves (YL = 27 species) and mature leaves (ML = 13 species). • Samples collected from trees and strata where monkey fed. • Toughness = (force x displacement of cutting) / area of cut. • Toughness units = J m-2 • Cuts (n = 351 tests) made perpendicular and across midrib.
Mechanical toughness instrument
Results
(r2 = 0.72; p < 0.01)
(r2 = 0.73; p < 0.01)
(r2 = 0.09; p = 0.07)
Ingestion Rate
Masticatory Frequency
Masticatory Rate
• Ingestion rate negatively correlates with leaf toughness
• Masticatory frequency positively correlates with leaf toughness
• No significant correlation between masticatory rate and leaf
• Mean = 5.57 ±1.64 g/min; Range = 2.50 - 8.62 g/min.
• Mean = 18.68 ± 7.00 chews/g; Range = 10.64 - 38.05 chews/g.
• YL ingestion rate significantly higher (5.98 ±1.58 g/min) than
• ML (23.83 ± 8.26 ) > YL (15.92 ±4.25 ) chews/ g (p < 0.01).
ML (4.67 ±1.46 g/min) (p < 0.01).
Leaf Toughness
toughness • Mean = 91.08 ± 7.17 chews/min; Range = 74.32 - 107.7 chews/min.
• Mean = 183.4 ± 83.04 J m-2; Range = 71.4 J - 388.5 J m-2. • YL significantly lower toughness values (155.3 ± 87.29 J m-2) than
• YL (91.12 ± 6.91 chews/min) and ML (91.01 ±7.46 chews/min) were not significantly different (p = 0.48).
ML (237.5 ± 64.27 J m-2) (p < 0.01). References
Discussion • Leaf toughness was highly variable among commonly consumed leaves and significantly influenced foraging efficiency. 6 • Mature leaves were tougher than young leaves when comparing across all plant species and within a given plant species. • More time and energy are required to comminute and ingest tougher leaves. Foraging on tougher leaves is potentially costly: expedites tooth wear 7and vulnerable to predation while foraging. 8
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Wright BW, Ulibarri L, O’Brien J, Sadler B, Prodham R, Covert HH, Nadler T. 2008. It’s tough out there: variation in the toughness of ingested leaves and feeding behavior among four Colobinae in Vietnam. Int J Primatol 29:1455-1466.
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Juvenile male feeding on Thevetia peruviana YL.
• Estimates of nutritional intake should factor in differences in ingestion rates not only among different plant items (e.g., fruits vs. leaves) but also among different leaf species. • Research that examines the relationships among food mechanical properties, foraging efficiency, and oral processing behaviors will provide valuable context for interpreting masticatory morphology.2, 4, 9 • Future work will examine C. a. palliatus dental microwear, mandibular morphology, and mandibular remodeling in relation to foraging behavior and dietary toughness.
Acknowledgements
Adult female feeding on Trema orientalis YL.
Supported by the National Science Foundation Graduate Research Fellowship under Grant No. 2012136655, Columbus Zoo and Aquarium, Nacey Maggioncalda Foundation, National Geographic Society, and Pittsburgh Zoo & PPG Aquarium. We recognize the Kenya Wildlife Society and National Commission for Science, Technology, and Innovation for permission to conduct this research. Thanks to Paul Opere and John Ndege for their help in behavioral data collection and plant sample collection.
