JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. We report on the bird communities of a set of 12 7-yr-old forested landbridge islands in Lago Guri, a 4300 km2 hydroelectric impoundment in the State of Bolivar, Venezuela. Birds were censused on all islands and at mainland control sites by spot mapping in 1993, and via point counts in 1995. Instead of orderly "nested sets" of species on landmasses of graded size, the species composition of small (-1 ha) and medium (11-12 ha) islands was highly variable. Spot mapping substantiated the occurrence of 58 species of forest-nesting birds, collectively, on the 11 small and medium islands, which supported means of only 9 and 12 resident species, respectively. No species was found on all islands, and only five species were found on as many as 7 of the 11 small and medium islands. The mean number of islands per resident species was 3.0 for the 11 islands. Transients of many species were detected on all islands, but were more frequent on near ('0.5 km from a larger landmass) than on far islands (?1.0 km from a larger landmass). A large majority of the populations on the 1-ha islands consisted of a single pair, implying that few such populations could have survived since isolation without new colonizations to replenish individuals lost to dispersal and mortality.Notwithstanding low species numbers, both census methods indicated that avian densities were approximately twice as high on the 1-ha islands as on the mainland. In contrast, two of three medium-sized islands supported anomalously low densities of approximately one-fifth the mainland level. Both islands retain relict populations of capuchin monkeys (Cebus olivaceus). One hundred percent of artificial nests set out on one of these islands were raided, whereas no more than 30% of nests were lost on any of the other islands or on the mainland. For small and medium islands, we conclude that the founding communities present when the waters of Lago Guri reached their final level have already collapsed and been reconstituted. Species loss on some islands may have been accelerated by relict populations of predators, such as capuchins. Changes in composition thus appear to have been driven by a combination of biological (nest predation) and stochastic processes (high turnover).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.