Studies on Neotropical Fauna and Environment Vol. 47, No. 3, December 2012,157–170 Faunal nestedness and species–area relationship for small non-volant mammals in “sky islands” of northern Venezuela Robert P. Anderson a,b,c *, Eliécer E. Gutiérrez a,b , José Ochoa-G. d , Franger J. García e & Marisol Aguilera f a Department of Biology, City College of the City University of New York, New York, NY, USA; b Graduate Center, City University of New York, New York, NY, USA; c Division of Vertebrate Zoology (Mammalogy), American Museum of Natural History, New York, NY, USA; d Cabañas Bougainvillae, Los Taques, Paraguaná, Falcón, Venezuela; e Departamento de Biología, Universidad de Carabobo, Valencia, Carabobo, Venezuela; f Departamento de Estudios Ambientales, Universidad Simón Bolívar, Caracas, Venezuela (Received 28 October 2011; accepted 26 October 2012) We study the biogeography of small non-volant mammals in mesic montane sky islands of northern Venezuela. Fieldwork, examination of museum specimens, and critical use of literature yielded species lists for the Cordillera de Mérida, Cordillera de la Costa, Serranía de San Luis, and Cerro Santa Ana. Fieldwork confirmed the species known from Cerro Santa Ana and added 12 species for the Serranía de San Luis. Richness decreases with smaller area. Furthermore, the faunas are highly nested, with taxa dropping out at successive depressions. Species deviating from nestedness provide a signal indicative of in situ speciation in rodents but not in marsupials. Keywords: biogeography; cloud forest; Didelphimorphia; endemism; Rodentia; Venezuela Introduction Islands provide key insights into ecology and evolu- tion (Lomolino & Heaney 2004). Furthermore, many similarities exist between real islands and disjunct patches of particular habitat types in terrestrial sys- tems. Often, such naturally fragmented habitats corre- spond to what have been termed sky islands – montane forests that transition abruptly into drastically dif- ferent, typically drier, vegetation in the surrounding lowlands (e.g. Brown 1971; Patterson 1982). Studies of these naturally fragmented systems can lend insight into important current environmental issues (Knowles 2001; Peterson 2003). A fascinating system of montane sky islands exists in north-central South America, where successive depressions separate various ranges of the Andes and several associated mountain chains (Figure 1). The first of these breaks occurs in northwestern Venezuela, where the Depresión del Táchira divides the Cordillera Oriental from the Cordillera de Mérida. The Depresión de Barquisimeto lies to the north of the Cordillera de Mérida and separates it from various sections of the Cordillera de la Costa and other smaller ranges that run roughly parallel to the Caribbean. Each of these disjunct ranges harbors montane evergreen forest, including cloud forest at higher elevations; in contrast, most of the vegetation in *Corresponding author. Email: anderson@sci.ccny.cuny.edu the surrounding lowlands originally corresponded to drier vegetation types (deciduous forests, thorn forests, natural savannas, and deserts; Huber 1997; Ataroff-S 2003; IGVSB 2003). Two especially isolated elements – the Serranía de San Luis and Cerro Santa Ana – hold particu- lar biogeographic interest (Matteucci 1987). To the north of the Cordillera de Mérida and northwest of the Cordillera de la Costa, the Serranía de San Luis (=San Luis) runs ca. 50 km and rises to an elevation of 1501 m (Steyermark 1975). Cerro Santa Ana (=Santa Ana) lies on the Península de Paraguaná approxi- mately 70 km north of the Serranía. Only ca. 4 km long, the Cerro rises abruptly from the lowlands and reaches an elevation of 830 m (supplementary Figure S2; Tamayo 1941, 1971). Although broad connections existed in earlier periods of lower sea level (e.g. the Last Glacial Maximum), the Península de Paraguaná was an island during marine introgressions such as at the Last Interglacial and is linked to the rest of the mainland today only by the narrow and sparsely vegetated Istmo de los Médanos (Lara & González 2007). Here, we study the biogeography of small non- volant mammals in this system, giving special empha- sis to the Serranía de San Luis and Cerro Santa Ana. Small non-volant mammals (in the Neotropics: ISSN 0165-0521 print/ISSN 1744-5140 online © 2012 Taylor & Francis http://dx.doi.org/10.1080/01650521.2012.745295 http://www.tandfonline.com Downloaded by [Smithsonian Institution Libraries] at 06:28 13 December 2012