Incorporating the Effects of Socioeconomic Uncertainty into Priority Setting for Conservation Investment MARISSA F. MCBRIDE, ∗ † KERRIE A. WILSON,† MICHAEL BODE,‡ AND HUGH P. POSSINGHAM† ∗ Environmental Science, School of Botany, University of Melbourne, Melbourne, Victoria 3010, Australia, email m.mcbride@pgrad.unimelb.edu.au †The Ecology Centre, School of Integrative Biology, The University of Queensland, Brisbane, Queensland 4072, Australia ‡School of Physical Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia Abstract: Uncertainty in the implementation and outcomes of conservation actions that is not accounted for leaves conservation plans vulnerable to potential changes in future conditions. We used a decision-theoretic approach to investigate the effects of two types of investment uncertainty on the optimal allocation of global conservation resources for land acquisition in the Mediterranean Basin. We considered uncertainty about (1) whether investment will continue and (2) whether the acquired biodiversity assets are secure, which we termed transaction uncertainty and performance uncertainty, respectively. We also developed and tested the robustness of different rules of thumb for guiding the allocation of conservation resources when these sources of uncertainty exist. In the presence of uncertainty in future investment ability (transaction uncertainty), the optimal strategy was opportunistic, meaning the investment priority should be to act where uncertainty is highest while investment remains possible. When there was a probability that investments would fail (per- formance uncertainty), the optimal solution became a complex trade-off between the immediate biodiversity benefits of acting in a region and the perceived longevity of the investment. In general, regions were prioritized for investment when they had the greatest performance certainty, even if an alternative region was highly threatened or had higher biodiversity value. The improved performance of rules of thumb when accounting for uncertainty highlights the importance of explicitly incorporating sources of investment uncertainty and evaluating potential conservation investments in the context of their likely long-term success. Keywords: biodiversity hotspots, conservation planning, conservation resource allocation, decision theory, in- vestment risk, Mediterranean Basin, optimization, socioeconomic uncertainty, systematic conservation assessment Incorporaci´ on de los Efectos de la Incertidumbre Socioecon´ omica en la Definici´ on de Prioridades para la Inversi´ on en Conservaci´ on Resumen: La incertidumbre en la planificaci´ on y los resultados de acciones de conservaci´ on que no es con- siderada hace que los planes de conservaci´ on sean vulnerables a cambios potenciales en condiciones futuras. Utilizamos un m´ etodo basado en la teor´ ıa de decisiones para investigar los efectos de dos tipos de incertidum- bre de inversi´ on sobre la asignaci´ on ´ optima de recursos para la conservaci´ on global para la adquisici´ on de tierras en la cuenca del Mediterr´ aneo. Consideramos la incertidumbre sobre (1) s´ ı la inversi´ on continuar´ ay (2) s´ ı los activos de biodiversidad adquiridos son seguros, que denominamos incertidumbre de transacci´ on e incertidumbre de ejecuci´ on respectivamente. Tambi´ en desarrollamos y probamos la robustez de diferentes re- glas generales para guiar la asignaci´ on de recursos cuando existen estas fuentes de incertidumbre. En presencia de incertidumbre en la habilidad de inversi´ on futura (incertidumbre de transacci´ on) la estrategia ´ optima fue oportunista, lo que significa que la inversi´ on prioritaria ser´ ıa donde la incertidumbre sea mayor mientras que la inversi´ on permanezca posible. Cuando hab´ ıa probabilidad de que las inversiones fallar´ ıan (incertidumbre Paper submitted May 10, 2007; revised manuscript accepted July 13, 2007. 1463 Conservation Biology Volume 21, No. 6, 1463–1474 C 2007 Society for Conservation Biology DOI: 10.1111/j.1523-1739.2007.00832.x