Identifying Conservation Priorities using a Return on Investment Analysis 187 Table Number of additional species protected for five measures of biodiversity by applying an ROI approach and four alternative priority setting approaches with a conservation budget of $100 million per year over 20 years Prioritization approach Total species richness Vertebrate species richness Plant species richness Endemic vertebrate richness Threatened vertebrates No of distinct vertebrates Return on investment Areas with endemic species Crisis biomes Highly threatened species per dollar Random 2524 1705 341 201 2231 1504 14 69 45 1910 1495 227 218 1683 1276 10 23 43 1571 208 1383 27 Source: Reproduced from Underwood EC, Shaw MR, Wilson KA, et al (2008) Protecting biodiversity when money matters: Maximizing return on investment PLoS One resource-allocation decisions is in its infancy, it is too soon to judge its effectiveness on this front What makes a good decision is the process by which it was generated, not the ultimate outcome From a philosophical standpoint, ROI analysis has a number of strengths relative to many existing approaches to conservation prioritization (whether this prioritization is explicit or not) These are mentioned throughout the article but are worth highlighting as they provide the foundation for the role and increasing use of ROI in conservation It acknowledges the importance of cost ROI analysis reflects a recognition that the investment required to achieve conservation outcomes is important in deciding where and how we work The resources available for conservation are limited, and directing them to the places with the most biodiversity does not necessarily lead to greatest protection of biodiversity Conservation prioritizations have often overlooked this basic and fundamental point This is despite numerous publications illustrating that ignoring cost in decisions about conservation priority is likely to lead to substantially less biodiversity being conserved than is possible for the same total resources (e.g., Bode et al., 2008; Carwardine et al., 2008a, b; Bottrill et al., 2009) In other words, it is grossly inefficient to ignore cost Similarly, high variation in the cost of taking conservation action (often orders of magnitude difference between alternatives) emphasizes the importance of considering cost in conservation decision making (Bode et al., 2008; Murdoch et al., 2011) It encourages transparency about assumptions and values Formulating ROI problems forces us to be explicit about the assumptions we are making Being explicit about value judgments is a basic tenet of decision theory, and yet many conservation prioritizations and decision-support systems contain hidden assumptions and value judgments For example, the widely used strategic planning process, Conservation Action Planning (TNC, 2007), uses a series of lookup tables to combine qualitative estimates of different aspects of threat to biodiversity (e.g., scope and severity) and produce an overall threat rank for the conservation feature of interest These tables use rules like ‘‘One High or Two Medium threat rankings yield an Overall Threat Rank of Medium.’’ Such statements contain many hidden values and risk tolerances, and yet their appropriateness is almost never considered before using the Conservation Action Planning process Although the term ‘‘value judgment’’ is commonly used in a pejorative sense, they are an important and perfectly reasonable part of conservation decision making, provided we are transparent about them Going through an ROI prioritization exercise has often served to illustrate inconsistencies and biases in conservation preferences that were concealed by earlier prioritization schemes It encourages the consideration of diminishing returns ROI analyses typically recognize that there are likely to be diminishing returns on our conservation actions For example, the more area you protect in a given ecoregion, the smaller the marginal gain in conservation value Although the notion of complementarity has been an important feature of systematic conservation planning for more than 30 years, the idea that the marginal benefit of conservation decreases even before some ideal target has been reached is relatively new This is not dissimilar to the concept that biodiversity with the least protection should be a higher priority than those with more protection The diminishing returns argument has both genuine ecological and value judgment underpinnings On the ecological side, biodiversity conservation is subject to diminishing returns because of the species–area curve (whereby the number of new species increases at a declining rate with increasing area) On the value side, many believe that for the sake of ecological equality, places with greater protection represent a lower priority than those with less protection It encourages accountability Decision-support tools are just that – support tools They should not be so prescriptive as to limit the ability to capitalize on opportunities However, an ROI analysis can serve to provide a transparent view of the value of particular opportunities, which will hopefully encourage decision makers to carefully justify decisions that have objectively poor ROI Framing ROI Problems As self-evident and straightforward as it might sound, being clear about the question that an ROI analysis is intended to answer is often one of the most contentious steps in conducting ROI analyses Clearly framing the problem involves being explicit about what resource-allocation decision the ROI