Sensitivity analysis of conservation targets in systematic conservation planning

Systematic conservation planning has rapidly advanced in the past decade and has been increasingly incorporated in multiple studies and conservation projects. One of its requirements is a quantitative definition of conservation targets. While the Convention on Biological Diversity aims to expand the world's protected area network to 17% of the land surface, in many cases such uniform policy-driven targets may not be appropriate for achieving persistence of various species. Targets are often set arbitrarily, often because information required for the persistence of each species is unavailable or unknown in the focal region. Conservation planners therefore need to establish complementary novel approaches to address the gaps in setting targets. Here, we develop and present a novel method that aims to help guide the selection of conservation targets, providing support for decision makers, planners, and managers. This is achieved by examining the overall flexibility of the conservation network resulting from conservation prioritization, and aiming for greater flexibility. To test this approach we applied the decision support tool Marxan to determine marine conservation priority areas in the eastern Mediterranean Sea as a case study. We assessed the flexibility of the conservation network by comparing 80 different scenarios in which conservation targets were gradually increased and assessed by a range of calculated metrics (e.g., the percentage of the total area selected, the overall connectivity). We discovered that when conservation targets were set too low (i.e., below 10% of the distribution range of each species), very few areas were identified as irreplaceable and the conservation network was not well defined. Interestingly, when conservation targets were set too high (over 50% of the species' range), too many conservation priority areas were selected as irreplaceable, an outcome which is realistically infeasible to implement. As a general guideline, we found that flexibility in a conservation network is adequate when similar to 10-20% of the study area is considered irreplaceable (selection frequency values over 90%). This approach offers a useful sensitivity analysis when applying target-based systematic conservation planning tools, ensuring that the resulting protected area conservation network offers more choices for managers and decision makers.