Ann. N.Y. Acad. Sci. ISSN 0077-8923 ANNALS OF THE NEW YORK ACADEMY OF SCIENCES Issue: The Year in Ecology and Conservation Biology Understanding local-scale drivers of biodiversity outcomes in terrestrial protected areas Megan D. Barnes, 1,2,3 Ian D. Craigie, 4 Nigel Dudley, 3,5 and Marc Hockings 3,6 1 Australian Research Council Centre of Excellence for Environmental Decisions, The University of Queensland, St. Lucia, Australia. 2 Centre for Biodiversity and Conservation Science, The University of Queensland, St. Lucia, Australia. 3 School of Geography Planning and Environmental Management, The University of Queensland, St. Lucia, Australia. 4 Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Australia. 5 Equilibrium Research, Bristol, United Kingdom. 6 UNEP-World Conservation Monitoring Centre, Cambridge, United Kingdom Address for correspondence: Megan Barnes, Centre for Biodiversity and Conservation Science, Level 5, Goddard Building, The University of Queensland, St. Lucia, Queensland 4067, Australia. megan.barnes@uq.edu.au Conservation relies heavily on protected areas (PAs) maintaining their key biodiversity features to meet global biodiversity conservation goals. However, PAs have had variable success, with many failing to fully maintain their biodiversity features. The current literature concerning what drives variability in PA performance is rapidly expanding but unclear, sometimes contradictory, and spread across multiple disciplines. A clear understanding of the drivers of successful biodiversity conservation in PAs is necessary to make them fully effective. Here, we conduct a comprehensive assessment of the current state of knowledge concerning the drivers of biological outcomes within PAs, focusing on those that can be addressed at local scales. We evaluate evidence in support of potential drivers to identify those that enable more successful outcomes and those that impede success and provide a synthetic review. Interactions are discussed where they are known, and we highlight gaps in understanding. We find that elements of PA design, management, and local and national governance challenges, species and system ecology, and sociopolitical context can all influence outcomes. Adjusting PA management to focus on actions and policies that influence the key drivers identified here could improve global biodiversity outcomes. Keywords: effectiveness; assessment; evaluation; national reserves; parks Introduction A key strategy for protecting biodiversity from anthropogenic threats has been the creation and maintenance of protected areas (PAs). 1,2 The essen- tial role that PAs play in reducing and preventing biodiversity loss is recognized by the 2020 Conven- tion on Biological Diversity (CBD) targets. 3 Con- sequently, they have received significant policy and legislative support, leading to rapid expansion of the global PA network in recent decades. Global cover- age now stands at over 15.4% of terrestrial surface area and at least 3.4% of the ocean. 4 Despite this rapid expansion, biodiversity loss continues, 5 including within PAs, 6,7 which vary widely in their ability to maintain biodiversity. Many PAs are not performing adequately, 6–9 meaning that they are unlikely to preserve biodiversity in per- petuity. Widespread PA failure would undermine national conservation strategies, so it is vital that we understand the drivers of success and failure. By doing so, we can promote those that facilitate the best outcomes and work to overcome those that impede long-term maintenance of biodiversity val- ues in PAs. Despite the importance of PAs in national strategies, there is limited empirical evidence about what factors influence their effectiveness, and what little evidence does exist is fragmented and often inaccessible. Measuring PA performance To understand the drivers of biodiversity outcomes in PAs, it is first necessary to be able to measure PA outcomes and performance. There are several axes of PA performance that may be considered impor- tant (e.g., cultural, economic, social), but the over- arching axis, and the one this review focuses on, doi: 10.1111/nyas.13154 1 Ann. N.Y. Acad. Sci. xxxx (2016) 1–19 C  2016 New York Academy of Sciences.