Percentage of area protected can substitute for more complicated structural metrics when monitoring protected area connectivity

Abstract

Protected area (PA) targets have become a hallmark of global conservation policies such as the recent Kunming-Montreal Global Biodiversity Framework, which requires signatory countries to establish new PAs while also monitoring gains to both PA network coverage and connectivity at large spatial scales. Policy makers tasked with implementing and monitoring progress toward these targets face the difficult decision about which connectivity metric to use, which is not always straightforward given existing data and software limitations. We empirically compare 17 of the most widely used structural connectivity metrics to determine how they capture change in a PA network as additional protected areas are added and assess whether mathematically simple metrics are a reasonable substitute for more complex metrics. We find that simply reporting the percentage of the total area that is protected is a viable way to capture connectivity gains in most landscapes. If a more involved metric is desired, we recommend the Integral Index of Connectivity, which was highly correlated with the percentage of area protected, produced similar results when measuring change in PA networks, and incorporates stepping stone movements through transboundary regions.