Dominance rank differences in the energy intake and expenditure of female Bwindi mountain gorillas
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Socioecological models predict that contest competition for clumped foods can lead to higher energy intake and lower energy expenditure for higher-ranking individuals. Here, we examine the relationships between dominance rank and energy intake and expenditure of female mountain gorillas in Bwindi Impenetrable National Park, Uganda (Gorilla beringei beringei). Bwindi gorillas have weak dominance relationships, feed on nonreproductive plant parts throughout the year, and consume fruit when it is seasonally available. We used behavioral observations on one group of gorillas and nutritional analysis of their major food items to calculate energy intake rates and estimated energy expenditure. Using linear mixed models, we found a significant positive relationship between dominance rank and energy intake rates, due to higher-ranking females having faster ingestion rates, rather than consuming foods with higher energy concentrations. Lower-ranking females did not spend significantly more time feeding to compensate for their lower energy intake rates. Lower-ranking females spent significantly more time traveling than higher-ranking females, leading to a negative relationship between dominance rank and energy expenditure. The combined results revealed a significant positive relationship between dominance rank and energy balance. Higher-ranking females did not spend longer feeding on fruit than lower-ranking ones, and the relationship between dominance rank and energy intake rates was not stronger when fruit was available. According to socioecological models, these results suggest that contest competition may be occurring with both fruit and nonreproductive plant parts, which would be consistent with growing evidence that nonreproductive plant parts can be contestable.
KeywordsDominance rank Energy balance Energy intake Energy expenditure Mountain gorillas
We thank the Ugandan Wildlife Authority and the Ugandan National Council of Science and Technology for permission to conduct research in Bwindi Impenetrable National Park. The Institute for Tropical Forest Conservation provided logistical support. We would like to thank all the field assistants for their dedication in the field, especially Dennis Musinguzi, Beda Turyananuka, Emmanuel Tibenda, Ngamganeza Caleb, Byaruhanga Gervasion, and Edson Nzabarinda. Robert Barigira assisted in plant identification. We are grateful to Sylvia Ortmann and her lab for plant nutritional analysis and Jessica Ganas for her work on the nutritional analysis. We also thank Roger Mundry and Colleen Stephens for statistical advice. We thank Christophe Boesch, Cyril Grueter, and Jessica Rothman for helpful discussion. This project was funded by the Max Planck Society.
This study complied with all Uganda Wildlife Authority regulations.
Conflict of interest
The authors declare that they have no conflict of interests.
- Baayen RH (2011) languageR: Data sets and functions with “analyzing linguistic data: a practical introduction to statistics.” R package version 1.4. http://CRAN.R-project.org/package=languageR
- Bates D, Maechler M, Ben B (2012) lme4: linear mixed-effects models using S4 classes. R package 0.999999-0. http://CRAN.R-project.org/package=lme4
- Committee on Animal Nutrition, Ad Hoc Committee on Nonhuman Primate Nutrition, National Research Council (2003) Nutrient requirements of nonhuman primates: second revised edition. The National Academies Press, Washington, DCGoogle Scholar
- Conklin-Brittain NL, Knott CD, Wrangham R (2006) Energy intake by wild chimpanzees and orangutans: methodological considerations and a preliminary comparison. In: Hohmann G, Robbins MM, Boesch C (eds) Feeding ecology in apes and other primates: ecology, physiology and behavioural aspects. Cambridge University Press, Cambridge, pp 445–471Google Scholar
- Field AP (2005) Discovering statistics using SPSS. SAGE Publications, LondonGoogle Scholar
- Fox J, Weisberg S (2011) An R companion to applied regression. SAGE, Thousand Oaks, CAGoogle Scholar
- Pusey A (2012) Magnitude and sources of variation in female reproductive performance. In: Mitani JC, Call J, Kappeler PM, Palombit RA, Silk JB (eds) The evolution of primate societies. University of Chicago Press, Chicago, pp 343–366Google Scholar
- R Development Core Team (2012) R: a language and environment for statistical computing. R foundation for statistical computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www.R-project.org/
- Robbins MM (2010) Gorillas - Diversity in ecology and behaviour. In: Campbell C, Fuentes A, MacKinnon K, Bearder S, Stump R (eds) Primates in perspective, 2nd edn. Oxford University Press, New York, pp 326–339Google Scholar
- Schülke O, Ostner J (2012) Ecological and social influences on sociality. In: Mitani JC, Call J, Kappeler PM, Palombit RA, Silk JB (eds) The evolution of primate societies. University of Chicago Press, Chicago, pp 196–219Google Scholar
- Schülke O, Chalise MK, Koenig A (2006) The importance of ingestion rates for estimating food quality and energy intake. Am J Primatol 68:951–965Google Scholar
- Sokal RR, Rohlf FJ (1995) Biometry: the principles and practices of statistics in biological research, 3rd edn. W. H, Freeman, New YorkGoogle Scholar
- van Schaik C (1989) The ecology of social relationships among female primates. In: Standen V, Foley R (eds) Comparative socioecology, the behavioral ecology of humans and other mammals. Blackwells, Oxford, pp 195–218Google Scholar