The role of forest structure, fragment size and corridors in maintaining small mammal abundance and diversity in an Atlantic forest landscape Renata Pardini a,*, Sergio Marques de Souza a, Ricardo Braga-Neto a, Jean Paul Metzger b a Departamento de Zoologia, Instituto de Biociencias, �� Universidade de Sa ��o Paulo, Rua do Mata ��o, Travessa 14, 101, CEP 05508-900, Sa ��o Paulo, SP, Brazil b Departamento de Ecologia, Instituto de Biociencias, �� Universidade de Sa ��o Paulo, Rua do Mata ��o, Travessa 14, 321, Cidade Universitaria, �� CEP- 05508-900, Sa ��o Paulo, SP, Brazil Received 13 October 2004 Abstract Using the abundance and distribution of small mammals at 26 sites in an Atlantic forest landscape, we investigated how species abundance and alpha and beta diversity are affected by fragment size and the presence of corridors. To account for the variability in forest structure among fragments, we described and minimized the influence of foliage density and stratification on small mammal data. Sites were distributed among three categories of fragment size and in continuous forest. For small and medium-sized catego- ries, we considered isolated fragments and fragments connected by corridors to larger remnants. Small mammal abundance and alpha and beta diversity were regressed against site scores from the first axis of a Principal Component Analysis on forest structure variables. Residuals were used in analyses of variance to compare fragment size and connectivity categories. Forest structure influ- enced total abundance and abundance of some species individually, but not the diversity of small mammal communities. Total abundance and alpha diversity were lower in small and medium-sized fragments than in large fragments and continuous forest, and in isolated compared to connected fragments. Three species were less common, but none was more abundant in smaller frag- ments. At least one species was more abundant in connected compared to isolated fragments. Beta diversity showed an opposite relationship to fragment size and corridors, increasing in small and isolated fragments. Results highlight the importance of second- ary forest for the conservation of tropical fauna, the hyper-dynamism of small isolated fragments and the potential of corridors to buffer habitat fragmentation effects in tropical landscapes. �� 2005 Elsevier Ltd. All rights reserved. Keywords: Habitat loss and fragmentation Corridors Connectivity Alpha and beta diversity Forest structure Hyper-dynamism 1. Introduction The negative consequences of habitat loss and frag- mentation to different aspects of biodiversity have been shown by a large number of theoretical and empirical studies, in different environments, and for a large array of taxa (Fahrig, 2003). By decreasing population size and thus increasing the influence of stochastic processes, habitat loss and fragmentation should increase extinc- tion rates, leading to a decrease in alpha diversity in remnants (Wilcox and Murphy, 1985) and an increase in beta diversity among them (Harrison, 1997 Loreau, 2000 Chase, 2003). Although species loss has been observed for different taxa in fragmented tropical 0006-3207/$ - see front matter. �� 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.biocon.2005.01.033 * Corresponding author. Tel.: +55 11 30917511 fax: +55 11 30917513. E-mail address: renatapardini@uol.com.br (R. Pardini). www.elsevier.com/locate/biocon Biological Conservation xxx (2005) xxx���xxx BIOLOGICAL CONSERVATION ARTICLE IN PRESS

landscapes (Laurance and Bierregaard, 1997), few studies focused on the increase in spatial variability in community composition among fragments (Harrison, 1997 Gilbert et al., 1998). Moreover, recent studies have brought to light the synergism between habitat fragmentation and a series of impacts induced by human activities in altered land- scapes (Laurance and Cochrane, 2001). In tropical for- ests in particular, forest structure, an important factor determining the occurrence of species and the structure of animal communities (Tews et al., 2004), is drastically altered in human landscapes by edge effects, selective logging, fire and the regeneration process (Malcolm, 1994 Malcolm and Ray, 2000 Cochrane, 2001 DeWalt et al., 2003). On the other hand, landscape elements that enhance functional connectivity among fragments, i.e., which in- crease the flow of individuals or genes, should favor recolonization or immigration rates and decrease local extinctions through the rescue effect (Brown and Kod- ric-Brown, 1977). Corridors are an evident aspect of the degree of structural connectivity among fragments, representing a clear and attainable strategy for the man- agement of fragmented landscapes. For this reason, a number of studies have tested the effectiveness of corri- dors (Simberloff et al., 1992 Beier and Noss, 1998). Cor- ridors may increase movement of individuals (Gonzalez et al., 1998 Haddad, 1999 Mech and Hallett, 2001), gene flow (Aars and Ims, 1999 Hale et al., 2001 Mech and Hallett, 2001) and population size (Dunning et al., 1995 Haddad and Baum, 1999 Uezu et al., in press), and may facilitate animal���plant interactions (Tewks- bury et al., 2002 Orrock et al., 2003). Few studies, how- ever, focused on the effects of corridors on the composition, richness (alpha diversity) and spatial vari- ability (beta diversity) of communities (Beier and Noss, 1998). The Brazilian Atlantic forest is one of the richest but also most endangered tropical forests in the world (Myers et al., 2000). Covering less than 8% of its ori- ginal distribution, conservation strategies for the Atlantic forest depend on information on how biodi- versity is maintained and affected in the remaining small and altered patches, and on information to help establish restoration plans. Small mammals, rodents and marsupials, may be considered a good group to help answer this type of question. They play an important ecological role in the Atlantic forest, influ- encing forest regeneration through the differential pre- dation on seeds and seedlings (Pizo, 1997 Vieira et al., 2003a) and the dispersal of seeds (Grelle and Gar- cia, 1999 Vieira and Izar, 1999 Pimentel and Tabar- elli, 2004). They also represent the most diverse ecological group of mammals in the Atlantic forest, where more than 90 species are found, of which around 43 are endemic (Fonseca et al., 1996). Despite the reduced number of studies that focused on the effects of the long-standing fragmentation on Atlantic forest small mammals (Fonseca and Robinson, 1990 Pires et al., 2002 Castro and Fernandez, 2004 Pardini, 2004), there are good indications that these ani- mals clearly respond to habitat and landscape altera- tions. Atlantic and Amazonian small mammals occupy a series of habitats that retain a forest structure, includ- ing secondary forest (Stallings, 1989 Fonseca and Rob- inson, 1990 Pardini, 2004), shade cocoa plantations (Pardini, 2004), linear corridors (Lima and Gascon, 1999) and forest edges (Malcolm, 1997a Pardini, 2004). The abundance of several species, however, is af- fected by foliage density and stratification (Malcolm, 1995 Gentile and Fernandez, 1999 Pardini, 2001 Grelle, 2003). Some of the species that are found mainly on the canopy as well as some of those that occupy the ground level decrease in abundance, while those found predominantly on the understory increase in abundance, in more disturbed or younger forest, where the under- story is denser and the canopy is more open (Malcolm, 1995 Pardini, 2001, 2004 Vieira et al., 2003b). With few exceptions, however, the great majority of Atlantic for- est small mammals do not occur in natural or anthropo- genic open habitats (Stallings, 1989 Stevens and Husband, 1998 Feliciano et al., 2002), and the rates of movement of individuals among Atlantic forest frag- ments surrounded by open fields are low (Pires et al., 2002), leading to extinctions in small fragments (Castro and Fernandez, 2004). Using the abundance and distribution of small mam- mals in 26 sites of an Atlantic forest landscape, we inves- tigated how species abundance and alpha and beta diversity are affected by fragment size and the presence of corridors. To account for the variability in forest structure among fragments, we described and minimized the influence of foliage density and stratification on small mammal data. 2. Methods 2.1. Study area Our study was carried out in Caucaia do Alto, lo- cated in the Cotia and Ibiuna �� municipalities, State of Sa ��o Paulo, Brazil, in a continuous forest and in a frag- mented landscape (Fig. 1). The altitude in the region varies from 850 to 1100 m and the relief is characterized by denudation, convex hills and inclinations of more than 15% (Ross and Moroz, 1997). Mean maximum temperature is 27 ��C and mean minimum temperature is 11 ��C. Rainfall is around 1300���1400 mm/year and it is seasonally variable, with the driest and coldest months between April and August. The vegetation in the region is a transition between the coastal Atlantic rain forest 2 R. Pardini et al. / Biological Conservation xxx (2005) xxx���xxx ARTICLE IN PRESS