title: When top-down becomes bottom up: behaviour of hyperdense howler monkeys (Alouatta seniculus) trapped on a 0.6 ha island.
abstract: 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.
authors.affiliation: Fairchild Tropical Botanical Garden, Coral Gables, Florida, United States of America.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Orihuela
authors.affiliation: Center for Tropical Conservation, Nicholas School of the Environment and Earth Sciences, Duke University, Durham, North Carolina, United States of America.
authors.forename: John
authors.initials: J
authors.lastname: Terborgh
authors.affiliation: Wildlife Research Group, The Anatomy School, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Natalia
authors.initials: N
authors.lastname: Ceballos
authors.affiliation: Department of Evolutionary Anthropology, Duke University, Durham, North Carolina, United States of America.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Glander
mesh_terms: D000374:Aggression; D000508:Alouatta / Q000254:growth & development / Q000502:physiology* / Q000523:psychology*; D000818:Animals; D001522:Behavior, Animal; D001835:Body Weight; D004032:Diet; D005260:Female; D006702:Homing Behavior; D062312:Islands; D008297:Male; D011156:Population Density
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