When top-down becomes bottom up: behaviour of hyperdense howler monkeys (Alouatta seniculus) trapped on a 0.6 ha island.
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Predators are a ubiquitous presence in most natural environments. Opportunities to contrast the behaviour of a species in the presence and absence of predators are thus rare. Here we report on the behaviour of howler monkey groups living under radically different conditions on two land-bridge islands in Lago Guri, Venezuela. One group of 6 adults inhabited a 190-ha island (Danto) where they were exposed to multiple potential predators. This group, the control, occupied a home range of 23 ha and contested access to food resources with neighbouring groups in typical fashion. The second group, containing 6 adults, was isolated on a remote, predator-free 0.6 ha islet (Iguana) offering limited food resources. Howlers living on the large island moved, fed and rested in a coherent group, frequently engaged in affiliative activities, rarely displayed agonistic behaviour and maintained intergroup spacing through howling. In contrast, the howlers on Iguana showed repulsion, as individuals spent most of their time spaced widely around the perimeter of the island. Iguana howlers rarely engaged in affiliative behaviour, often chased or fought with one another and were not observed to howl. These behaviors are interpreted as adjustments to the unrelenting deprivation associated with bottom-up limitation in a predator-free environment.
Published Version (Please cite this version)
Orihuela, Gabriela, John Terborgh, Natalia Ceballos and Kenneth Glander (2014). When top-down becomes bottom up: behaviour of hyperdense howler monkeys (Alouatta seniculus) trapped on a 0.6 ha island. PLoS One, 9(4). p. e82197. 10.1371/journal.pone.0082197 Retrieved from https://hdl.handle.net/10161/16153.
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John W. Terborgh is a James B. Duke Professor of Environmental Science and is Co-Director of the Center for Tropical Conservation at Duke University. He is a member of the National Academy of Science, and for the past thirty-five years, he has been actively involved in tropical ecology and conservation issues. An authority on avian and mammalian ecology in neotropical forests, Dr. Terborgh has published numerous articles and books on conservation themes. Since 1973 he has operated a field station in Peru's Manu National Park where he has overseen the research of more than 100 investigators. Dr. Terborgh earlier served on the faculties of the University of Maryland and Princeton University. In June 1992 he was awarded a John D. and Catherine T. MacArthur Fellowship in recognition of his distinguished work in tropical ecology, and in April 1996 he was awarded the National Academy of Science Daniel Giraud Elliot medal for his research, and for his book Diversity and the Tropical Rainforest. He has served on several boards and advisory committees related to conservation, including the Wildlands Project, Cultural Survival, The Nature Conservancy, The World Wildlife Fund and both the Primate and Ecology Specialist Groups of the International Union for the Conservation of Nature.
Primate ecology and social organization: the interaction between feeding patterns and social structure; evolutionary development of optimal group size and composition; factors affecting short and long-term demographic changes in stable groups; primate use of regenerating forests.
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