Combining plant and bird data increases the accuracy of an Index of Biotic Integrity to assess conservation levels of tropical forest fragments

Abstract

Rapid ecological assessment methods, such as Rapid Ecological Assessments (REA) and Indexes of Biotic Integrity (IBI) are useful tools for the selection of priority areas for biodiversity conservation. However, the majority of rapid assessment methods are based on data from a single taxonomic group; a multi-taxa index should provide a more integrated evaluation of the response of a disturbed system. In this study, we propose a new, easy-to-follow, integrated Index of Biotic Integrity (IBIint) which combines plants and birds to assess ecological integrity of tropical forest fragments. This integrated index combines the information of two previously developed rapid assessment methods: REA for plants and IBI for birds. These two indexes were built based on key vegetation features and on levels of sensitivity to forest fragmentation of bird species. We applied IBI, REA and the new IBIint indexes on the characterization of 10 forest fragments and in a large continuous forest block (reference area). We also tested the correlation of the proposed index (IBIint), REA and IBI with patch size, forest amount and connectivity at four spatial scales (250, 500, 1000, 1500m). Our hypothesis was that IBIint would be more correlated with landscape metrics than the REA and IBI. As expected, IBIint was the more accurate index once it was explained by all landscape variables: area of forest fragments; forest connectivity; and, percentage of forest cover at four spatial scales. REA and IBI were explained only by one of those parameters. We conclude that IBIint can be an excellent tool to aid conservationists and managers for defining conservation strategies in scenarios with fast habitat loss.