The impacts of habitat loss and fragmentation upon the maintenance of biodiversity in tropical ecosystems

Abstract

Habitat loss and fragmentation are major threats to biodiversity on a global scale. Human modified landscapes now comprise large areas of the globe, heavily contributing to the observed decline in biodiversity. By understanding the processes governing species communities in these fragmented landscapes we may be better able to manage them in a way that provides conservation benefits. The first part of this thesis focuses on dispersal in complex landscapes with Chapter 2 taking a regional view, examining connectivity across the whole Brazilian Atlantic Forest from a functional perspective and Chapter 3 investigating movement within local landscapes. We found that from the perspective of its fauna the Brazilian Atlantic Forest is functionally fragmented, with few areas remaining that are able to support large populations. At the local scale species exhibited clear threshold responses to changing forest cover with dispersal ability and home range size important determinants. The second part analyses bird diversity patterns across fragmented landscapes. Chapter 4 looks at alpha-diversity and composition, considering different land-uses and habitat types across a fragmentation gradient. Chapter 5 examines beta-diversity within habitats as well as between habitat types and landscapes. Bird community composition was found to differ between land use types as well as between habitats. Plantation forest matrices were able to mitigate isolation and area effects, retaining forest species. Beta-diversity within habitats was found to remain constant, whereas between habitat beta-diversity was high when comparing contrasting habitats. Turnover between habitat types is able to offset decreases in alpha-diversity, contributing to the maintenance of gamma-diversity. At the landscape level dissimilarity patterns were heavily governed by forest cover, suggesting a range of habitat amounts are needed to preserve the full bird community. Overall, although habitat loss and fragmentation are highly detrimental for biodiversity, mitigation via management changes are possible.