A simple and practical measure of the connectivity of protected area networks: The ProNet metric

Measuring connectivity is key to track progress toward broad conservation goals, such as the United Nations Convention on Biological Diversity's proposed Post-2020 Global Biodiversity Framework. The framework includes an area-based target for the protection of 30% of lands and seas globally-through well-connected systems of protected areas. Although the field of connectivity science has grown rapidly, limited progress has been made in tracking conservation connectivity in practice. This is in part due to the lack of a standardizing framework to clarify different purposes, approaches, and datasets-particularly in differentiating a metric from its application within a broader connectivity framework-as well as a benchmark to quantitatively compare alternative approaches. To address this science-practice gap, we developed a novel metric of connectivity called the Protected Network metric (ProNet). ProNet is designed to assess the structural connectivity of a protected area network in a way that can be easily described, clearly communicated, and rapidly computed at high resolution. We evaluated how ProNet adheres to fundamental conservation science principles using a library of hypothetical landscapes, compared it to two commonly used existing connectivity metrics, and demonstrated its performance in assessing connectivity for a set of real-world landscapes selected across the gradient of human modification. More broadly, ProNet is a powerful tool to galvanize emerging connectivity conservation as a countermeasure to increasing fragmentation of global ecosystems.