Relative effects of fragment size and connectivity on bird community in the Atlantic Rain Forest: Implications for conservation
Introduction
Habitat loss and fragmentation are pointed as main threats to biodiversity conservation (Wilcox and Murphy, 1985, Fahrig, 2003). These two processes create landscapes where fragments are relatively small and poorly connected (With, 1997, Fahrig, 2003). In these situations, fragment size and landscape connectivity are suggested as key structural features influencing species persistence (Fahrig and Merriam, 1985, Fahrig and Merriam, 1994, Taylor et al., 1993, Hanski and Simberloff, 1997, Metzger and Décamps, 1997, Beier and Noss, 1998, Metzger, 2000, Antongiovanni and Metzger, 2005). Fragment size is considered to be related to population size, and thus is associated with the extinction probability in a given patch (Temple and Cary, 1988, Roth and Johnson, 1993, Jules, 1998; but see Debinski and Holt, 2000, Bowman et al., 2002). Landscape connectivity, which is a measure of the capacity of the landscape to facilitate biological flows among habitat patches (for a complete discussion of this terminology, see Fischer and Lindenmayer, 2007), is related with (re)colonization (Fahrig and Merriam, 1985, Hanski and Simberloff, 1997, Franken and Hik, 2004) and rescue effects (Brown and Kodrick-Brown, 1977), key processes determining population maintenance in fragmented landscapes (Fahrig and Merriam, 1985, Hanski and Simberloff, 1997, Fahrig, 2003, Ewers and Didham, 2006, Fischer and Lindenmayer, 2007).
Few studies have compared the relative importance of connectivity and fragment size for the maintenance of species in fragmented landscapes (Turner, 1996, Ewers and Didham, 2006). Usually, fragment size is the most significant predictor of species richness for all taxa, and connectivity is only a secondary predictor (Drinnan, 2005). However, there are situations where connectivity is as important as or even more important than size, especially for small fragments situated near large ones (Metzger, 2000) or when inter-habitat matrix permeability is high (Pardini, 2004, Faria et al., 2006). Some authors argued that below a 30% habitat cover threshold, habitat configuration, i.e. the spatial distribution of habitat in the landscape, including its structural connectivity, becomes particularly relevant the species persistence (Andrén, 1994, Fahrig, 2003, Radford et al., 2005). It has also been hypothesized that connectivity can modulate species-area relationships (Bender and Fahrig, 2005, Ewers and Didham, 2006, Metzger, 2006). Apparently, in less connected landscapes, the loss of species with fragment area reduction is intensified when compared with well connected ones (Metzger, 2006).
To address these problems and to provide a more concrete support for management and conservation actions, in this study we analyzed the relative effects of patch size and connectivity for the understory bird community richness and abundance in a fragmented Atlantic Rain Forest region. Particularly, we considered three sets of hypotheses: (i) higher importance of area; (ii) higher importance of connectivity; and (iii) importance of both aspects. We discuss the implications of our results for biodiversity conservation not only for the Atlantic Rain Forest but also for other regions.
Section snippets
Study area
The studied landscape has 10,063 ha (SW 47°07′27″23°47′12″ and NE 47°02′10″23°40′47″) and is located in the crystalline Plateau of Ibiúna (Ponçano et al., 1981), state of São Paulo, south-eastern Brazil (Fig. 1). This is part of the Atlantic Rain Forest, one of the most rich (Myers et al., 2000) and threatened regions of the world, where less than 8% of the original vegetation cover is left (Myers et al., 2000, SOS Mata Atlântica/INPE, 2002). Altitude ranges from 850 to 1100 m asl and the climate
Community structure
A total of 1293 individuals of 62 species were recorded during 9137 net/hours of sampling at the 17 fragments. Observed species composition, richness and abundance per site varied considerably, both for all species and within each of the functional groups (Table 1).
Community models
The three best models to explain total community richness with evidence ration <1.5 summed 51% of the wAIC and contained only connectivity variables by short linkage distances (⩽20 m) and corridor connections (Table 2). AREA was only
Relative importance of connectivity and area
Contrary to the expected from the literature, connectivity was more important than fragment area in predicting community and functional group richness. Landscapes with high connectivity, where fragments are close to each other and/or linked by corridors, provide the possibility for birds to use more than one fragment to obtain the necessary resources to survive, in daily or occasional movements (Andrade and Marini, 2001, Lees and Peres, 2008). Such landscape complementation (sensus Dunning et
Acknowledgement
This work belongs to the “Biodiversity conservation in fragmented landscapes at the Atlantic Plateau of São Paulo” project and was supported by the State of São Paulo Research Foundation (FAPESP n. 99/05123-4) and by The National Council for Scientific and Technological Development (CNPq n. 69014416). We wish to thank the land owners for allowing us to work on their properties. Special thanks for all our many field assistants, without them field work would have been impossible. Thanks for D.
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