Reconciling ‘irreplaceability’ and ‘importance’
The expansion of the world’s protected area network is often held up as a measure of global progress towards effective biodiversity conservation. However, having more protected areas does not necessarily mean better biodiversity outcomes.
In the past, two main approaches have been used to identify priority sites for biodiversity conservation: one based on species thresholds, such as those used to identify Important Bird and biodiversity Areas (IBAs), the other based on sites' complementarity, where sites for protection are identified to complement, rather than replicate, each other and the contribution of each site in achieving biodiversity conservation targets (its 'irreplaceability') is measured.
The orange-bellied parrot is endemic to Australia and critically endangered. Eighteen IBAs have been identified in Australia for the presence of this species. (Photo: © Jeremy Ringma.)
After decades of parallel development between threshold- and complementarity-based approaches, and in light of a pressing need to find shared strategies for an efficient expansion of protected areas, we brought together these approaches by performing a complementarity-based analysis of irreplaceability in IBAs. We focused on three regions with comprehensive IBA inventories and bird distribution atlases: Australia, southern Africa, and Europe.
We found that irreplaceability values were significantly higher inside IBAs than outside of them. The differences were much larger in Australia and much smaller in Europe. This is likely because Australia has more restricted-range birds and fewer IBAs than Europe. In fact, in all regions we found that higher irreplaceability values in IBAs were associated with the presence and number of restricted-range species. The relationship between higher irreplaceability and presence of restricted range species is not surprising: representation targets for widespread species can typically be met under many different spatial solutions; whereas, there are relatively few options for meeting targets for small-range species.
The correspondence between threshold-based and complementarity-based approaches can be complex. Sites with species below IBA-threshold levels could still be important to efficiently achieve species’ representation targets, especially when they have high levels of complementarity with other sites. On the other hand, a site may be of particular importance for a given species (eg, if the species congregates there) and be identified as an IBA even if it has low irreplaceability. We thus stress the importance of complementing the threshold-based identification of important biodiversity sites with the systematic identification of irreplaceable sites.
Recently the IUCN has undertaken a process to consolidate global standards for the identification of Key Biodiversity Areas, which builds on existing approaches such as IBAs. Our results informed this process and in particular a proposed criterion for irreplaceability that will allow the new KBA standard to draw on the strengths of both threshold-based and complementarity-based approaches.