Mastozoología Neotropical ISSN: 0327-9383 [email protected] Sociedad Argentina para el Estudio de los Mamíferos Argentina Mena, José L.; Medellín, Rodrigo A. HABITAT COMPLEXITY AND SMALL MAMMAL DIVERSITY ALONG AN ELEVATIONAL GRADIENT IN SOUTHERN MEXICO Mastozoología Neotropical, vol. 24, núm. 1, julio, 2017, pp. 121-134 Sociedad Argentina para el Estudio de los Mamíferos Tucumán, Argentina Available in: http://www.redalyc.org/articulo.oa?id=45753369010 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Mastozoología Neotropical, 24(1):121-134, Mendoza, 2017 Copyright ©SAREM, 2017 http://www.sarem.org.ar Versión impresa ISSN 0327-9383 http://www.sbmz.com.br Versión on-line ISSN 1666-0536 Artículo HABITAT COMPLEXITY AND SMALL MAMMAL DIVERSITY ALONG AN ELEVATIONAL GRADIENT IN SOUTHERN MEXICO José L. Mena1 and Rodrigo A. Medellín2 1 Museo de Historia Natural Vera Alleman Haeghebaert, Universidad Ricardo Palma, Lima, Perú. [Correspondencia: José L. Mena <[email protected]>] 2 Instituto de Ecología, Universidad Nacional Autónoma de México, Ciudad Universitaria, D. F., México. ABSTRACT. We tested the hypothesis that habitat complexity explains alpha diversity of nonvolant small mammals along an elevational gradient in southern Mexico. During October-November 2003, we conducted fieldwork on the Pacific slope of El Triunfo Biosphere Reserve. Small mammal trapping was conducted using standardized techniques (trap lines and pitfalls) along an elevational gradient between 500 and 2100 m elevation. Habitat assessment as indicated by vegetation complexity and diversity was conducted at each site (N = 12). Nine species and 148 individuals were captured in 8400 trap-nights. Results indicate that non volant small mammal diversity increases with habitat complexity. In addition, our study shows that the spatial pattern of diversity cannot be attributed to spatial autocorrelation. RESUMEN. Complejidad de hábitat y diversidad de mamíferos pequeños en un gradiente altitudinal en el sur de México. Probamos la hipótesis de que la complejidad del hábitat explica la diversidad (diversidad alfa) de mamíferos pequeños no voladores a lo largo de un gradiente de elevación en el sur de México. El trabajo de campo se realizó entre octubre y noviembre de 2003, en la vertiente del Pacífico de la Reserva de la Biosfera El Triunfo. La captura de mamíferos pequeños se llevó a cabo utilizando técnicas estandarizadas (líneas de trampeo y trampas de caída) a lo largo del gradiente de 500 a 2100 m de elevación. El hábitat fue evaluado con base en la complejidad y diversidad de la vegetación en cada sitio evaluado (N = 12). Nueve especies y 148 individuos fueron capturados en 8400 noches-trampa. Los resultados indican que la diversidad de mamíferos pequeños aumenta con la complejidad del hábitat. Además, nuestro estudio muestra que el patrón espacial de la diversidad encontrado no está influenciado por la autocorrelación espacial. Key words: Alpha diversity. Elevational gradient. Habitat complexity. Mexico. Small mammals. Palabras clave: Complejidad de hábitat. Diversidad alfa. Gradiente de altitud. Mamíferos pequeños. México. Recibido 30 enero 2017. Aceptado 27 marzo 2017. Editor asociado: J Morrone 122 Mastozoología Neotropical, 24(1):121-134, Mendoza, 2017 JL Mena and RA Medellín http://www.sarem.org.ar - http://www.sbmz.com.br INTRODUCTION taposition), source-sink dynamics and habitat heterogeneity (Brown, 2001; Lomolino, 2001; The study of local elevational gradients has Grytnes and McCain, 2007). However, eleva- great potential for increasing our knowledge tional gradients in species richness result from about both regional and global scale diver- a combination of ecological and evolutionary sity processes and the implications of climate processes, and thus, may not reflect one over- change. Indeed, elevational gradients have been riding force (Lomolino, 2001; Wu et al., 2013). reassessed in recent years (Brown, 2001; Lo- Certainly, habitat heterogeneity has a large molino, 2001; Mena and Vázquez-Domínguez, effect on species richness, but the relevant type 2005; McCain, 2007b; Guo et al., 2013) due to of heterogeneity will depend on the species changing perspectives on their interpretation. group and the scale of study (Brown, 2001; Elevational gradients can be used as natural Grytnes and McCain, 2007; Rowe et al., 2015). experiments, allowing for rigorous testing of Specifically, habitat structure appears to be hypotheses elicited by specific questions, such the most important factor describing diversity as effects of small spatial scale or elevational of terrestrial small mammals (August, 1983; trends in abiotic factors (Grytnes and Mc- Medellín and Equihua, 1998; Lambert et al., Cain, 2007). 2006; Mena and Medellín, 2010); however, There are two ways to quantify elevational this hypothesis has not been tested rigorously patterns in species richness: alpha and gamma along elevational gradients. Specifically, the diversity studies (McCain, 2005). Alpha diver- habitat complexity or habitat structure hy- sity studies use local field sampling of plots pothesis predicts that alpha diversity should along a transect, usually on one mountain slope, vary with local habitat complexity, and peak preferably with equal sampling effort at each at elevations characterized by higher habitat elevational band; and gamma diversity studies complexity (MacArthur, 1964; MacArthur, use regional data from previously collected 1972; Rosenzweig, 1992). Here, we examine specimens and field records from an entire this hypothesis in order to understand if this mountain or mountainous region (McCain, explains species richness along an elevational 2005; McCain, 2007a). Clearly, the observed gradient in southern Mexico. In addition, we elevational trend in species varies among groups explore whether the spatial autocorrelation of organisms. The most commonly observed (Koenig and Knops, 1998; Overmars et al., patterns are decreasing richness with increas- 2003) can influence the resulting elevational ing elevation (amphibians, bats and reptiles) gradient in species richness. Testing spatial (Sánchez-Cordero, 2001; Patterson et al., 1996; autocorrelation is helpful to address an essen- Sergio and Pedrini, 2007; Chettri et al., 2010), tial question for this type of studies: method- a low plateau (high diversity across most of the ologically, what elevational interval is useful to lower portion of the gradient then decrease assess elevational patterns in species richness [birds, reptiles]) (McCain, 2009; McCain, 2010), (e.g., 250 or 500 m intervals). This approach or a humped pattern with a richness peak at can be very helpful for selection of sites along intermediate elevations (mainly in nonvolant elevational gradients where researchers will small mammals and plants) (Kessler, 2001; conduct small mammal inventories. Usually, McCain, 2005; Cardelús et al., 2006). sampling sites along elevational gradients are The explanations commonly offered for selected as vegetation changes; however, there elevational patterns in species richness can are other ways to determine their location. In be grouped into four categories: climatic hy- this context, spatial correlation analysis is a potheses based on current abiotic conditions, useful tool to investigate mechanisms operating spatial hypotheses of area and spatial constraint, on species richness at different spatial scales historical hypothesis invoking processes occur- (Diniz-Filho et al., 2003). Indeed, this method ring across evolutionary timescales, and biotic is often used to assess the relationship between hypotheses such as community overlap (jux- variables along gradients. SMALL MAMMALS AND ELEVATIONAL GRADIENT IN MEXICO 123 MATERIAL AND METHODS 20 °C and annual precipitation between 2500-4500 mm (Williams-Linera, 1991; INE, 1998; Morón-Ríos Study area and Morón, 2001). Annual mean temperature at elevations between 1000 and 2000 m is 18-22 °C, The study was carried out in the El Triunfo Bio- with annual precipitation between 2000-3000 mm; sphere Reserve and its buffer zone (Fig. 1), on below 1000 m, annual mean temperature is 26 °C, the Pacific slope of the Sierra Madre de Chiapas, and annual precipitation between 2500-4000 mm southeastern Mexico (15° 09’10’’-15° 57’02’’N, 92° (INE, 1998). 34’04’’-93° 12’42’’W). This reserve is one of the Long and Heath (1991) and Williams-Linera few relatively undisturbed Mexican cloud forests. (1991) provide detailed information on vegetation The Pacific slope descends from the highest peak, and climate at El Triunfo. This reserve protects Cerro El Triunfo (2450 m a.s.l.), with steep slopes 10 of the 19 vegetation types found in Chiapas, influenced by erosion and landslides. Slopes level including large areas of the remaining stands of off somewhat at mid-elevations; below 800 m, land Central American cloud forest (Breedlove, 1981). is more influenced by agriculture (mainly coffee The vegetation types that cover the Pacific slope of plantations), ranching, and human settlement. The El Triunfo are tropical evergreen forest (< 800 m), wet season extends from May to October and the oak forest (800-1200 m), montane rainforest (1200- dry season from November to April. Annual mean 1600 m), pine forest (1600-1800 m), and upper cloud temperature above 2000 m elevation is between