Short noteEffects of forest fragmentation, anthropogenic edges and fruit colour on the consumption of ornithocoric fruits
Introduction
Since the conversion rate of tropical forests into disturbed habitats exceeds 1.2% annually, studies on the effects of forest fragmentation on the ecology of plants and animals are especially relevant to management of isolated forest remnants (Laurance and Bierregaard, 1997). One of the major changes brought by habitat fragmentation is an increase in the proportion of the edge (Kapos et al., 1997). Edge effects include decreasing humidity and increasing light and temperature (Murcia, 1995, Kapos et al., 1997) which may ultimately affect plant recruitment and survival (Benetiz-Malvido et al., 1999). Another important issue related to fragmentation is potential disruption of key mutualistic interactions between animals and plants, including pollination and seed dispersal (Aizen and Feinsinger, 1994, Santos and Telleria, 1994).
Forest fragmentation and the resulting anthropogenic edges may alter the abundance of fruiting plants and frugivorous birds (Stiles, 1980, Restrepo and Gomez, 1998, Restrepo et al., 1999). However, very few studies have evaluated how anthropogenic edges and habitat fragmentation affect the mutualistic process of frugivory and seed dispersal (Restrepo and Gomez, 1998, Restrepo et al., 1999).
A large proportion of vascular plants in Neotropical rain forests is dispersed by birds or mammals (Foster et al., 1986, Howe and Westley, 1988, Morellato and Leitao-Filho, 1992). These include canopy tree species with large seeds dispersed by specialized large frugivores (such as toucans, guans, and large cotingas) (Howe and Smallwood, 1982) which are prone to become vulnerable due to dispersal failure in fragmented forests (Silva and Tabarelli, 2000, Galetti, 2001). Understorey small fruits, on the other hand, are consumed by a wide variety of generalist birds, including manakins, tanagers and flycatchers (Wheelwright et al., 1984, Loiselle and Blake, 1999), which are not as highly affected by fragmentation (Willis, 1979, Aleixo and Vielliard, 1995).
A key challenge to understand the relationship between fruit and frugivore is to relate fruit morphology and accessibility to removal rate by birds (Levey et al., 1984, Moermond et al., 1986, Murray et al., 1993). Most bird-dispersed understorey fruits are easily accessible and coloured black (or dark purple), red or sometimes white (Wheelwright and Janson, 1985), such as Melastomataceae and Rubiaceae's fruits. This plant guild, although important to maintain at least small frugivore birds (Gilbert, 1980, Galetti and Stotz, 1996, Silva et al., 2002), has not considered threatened by habitat modification.
In this paper we examined how forest size, anthropogenic edge, and fruit colour influence the probability of understorey fruit consumption by birds and if each one these factors can influence the effect of the other.
Section snippets
Study areas
The Brazilian Atlantic forest is one of the most threatened ecosystems in the world and it is estimated that only 5% of the original area remains (ca. 60,000 km2) distributed in several small fragments and a few large forests (Ministério do Meio Mabiente, 2000). The semideciduous forests of the interior of the Atlantic forest (see Oliveira-Filho and Fontes, 2000) are especially in peril and less than 2% of these forest areas were left (Viana and Tabanez, 1996).
We studied eight semideciduous
Results
The fragment size, habitat and fruit colour significantly affected the probability of fruit consumption (Table 2). More fruits were pecked in large fragments compared to small fragments and at the edge compared with forest interior (Table 2; Fig. 1). Red and black fruits were equally consumed and both were more consumed than white fruits (Bonferroni a posteriori test: Black×Red, P=1.00; Black×White, P=0.002 and Red×White, P=0.001) (Fig. 1).
The interactions of size×colour and size×colour
Discussion
This study is the first to document how forest size, anthropogenic edge and fruit colour affect the probability of fruit consumption by birds. Our results have shown that fruits located on the edge of the forest also have higher probability of consumption than in the forest interior. Two main reasons may explain this result. First, forest exhibits much variation in light environments, and this can affect the communication between birds and fruits (Endler, 1993). Understorey ornithocoric fruits
Acknowledgments
We thank M.A. Pizo, P. Jordano, and D. Levey for useful comments on the manuscript and A.J. Underwood and R.V. Lenth for help in statistical analysis. We would like to thank the Instituto Florestal for permission to work in their reserves. This project received financial support from FAPESP (Proc. 96/10464-7, 01/10300-4). M. Galetti thanks CNPq (Proc. 300025/97-1), C. P. Alves-Costa (FAPESP Proc. 99/02355-1) and E. Cazetta (CNPq-PIBIC).
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