Current status of vertebrate diversity in anthropogenic and natural ecosystems in south-western Sri Lanka

Fragmentation of natural habitats is one of the major threats to long term conservation of biodiversity in Sri Lanka. Establishing corridors to link these natural habitat patches is one of the simplest strategies that can be used to address this threat. However, it is not possible to establish forest corridors everywhere and therefore alternate strategies need to be developed. This study was undertaken to test whether agro-ecosystems could be used as permeable matrices to link natural habitat patches. Four sites with different land use types were selected in the south-western region of Sri Lanka, where the highest level of habitat fragmentation occurs. These four sites represent three agro-ecosystems (tea, rubber and oil palm) and a natural ecosystem. Presence of herpetofauna, birds and large mammals in these four sites were enumerated using the quadrate sampling method (8 x 8 m) for herpetofauna and the line transect method for birds and mammals. At each site, sampling was carried out from September 2002 to November 2004. A total of 187 species of vertebrates were recorded from the four sites. This comprised 53 species of herpetofauna (41 species of reptiles and 12 species of amphibians), 99 species of birds and 35 species of mammals. Overall species richness (178) as well as the species richness of each of the three major taxa studied, namely, herpetofauna (51), birds (97) and mammals (30) were found to be the highest in the natural forest compared to the three agro-ecosystems. The agro-ecosystems were used by a large number of vertebrate species. However, the species assemblage in these agro-ecosystems was dominated by common species and comprised a few species that are threatened or endemic to Sri Lanka, compared to the natural forest. Therefore, it can be concluded that agro-ecosystems are important for maintaining population densities of common species. Further, this study clearly demonstrates the value of natural forests for preservation of threatened and endemic vertebrates. Since agro-ecosystems are not utilized by highly specialized threatened and endemic species, it is unlikely that this type of land use will create a permeable matrix among fragmented natural forests for such species.