1325 Conservation Biology, Pages 1325–1334 Volume 15, No. 5, October 2001 Using Phylogenetic Diversity Measures to Set Priorities in Conservation: an Example from Southern South America PAULA POSADAS,*‡ DANIEL R. MIRANDA ESQUIVEL,† and JORGE V. CRISCI* *Laboratorio de Sistemática y Biología Evolutiva (LASBE), Museo de La Plata, Paseo del Bosque, 1900 La Plata, Argentina †Universidad Industrial de Santander, AA 678, Bucaramanga, Colombia Abstract: Phylogenetic diversity measures rank areas for biodiversity conservation priorities based on infor- mation encoded in phylogenies (cladograms). The goal of these ranks for conservation is to consider as many factors as possible that provide additional taxic information, such as taxa richness, taxa distributional pat- terns, area endemicity, and complementarity between areas. At present there are many measures that con- sider phylogenetic information, including node-based, genetic-distance, and feature-based measures. We de- vised a modified phylogenetic node-based index that we call “taxonomic endemicity standardized weight,” which considers not only the taxonomic distinctness of the taxa that inhabit a given area but their endemic- ity as well. Once the standardized weight of the taxonomic endemicity identifies the area of highest priority, complementarity can be used to identify the second area and so on. We used this node-based index to rank priority areas for conservation in southern South America, and we compared the results of our rankings to results based on other node-based indexes. Our index identified Santiago district, in Central Chile province, as the highest priority area for conservation, followed by Maule, Malvinas, and districts of Subantarctic prov- ince. Malvinas exhibits greater complementarity relative to Santiago than Maule does, however, so Malvinas is ranked second in priority. Indexes based on phylogenetic information measure the evolutionary compo- nent of biodiversity and allow one to identify areas that will ensure the preservation of evolutionary poten- tial and phylogenetically rare taxa. The modified index we propose is sensitive to taxic distinctness and ende- micity as well and allows information from diverse taxa to be combined (i.e., different cladograms). The use of complementarity allows for preservation of the maximum quantity of taxa in a minimal number of pro- tected areas. Utilización de Medidas de Diversidad Filogenética para Definir Prioridades en Conservación: un Ejemplo del Sur de América del Sur Resumen: Las medidas de diversidad filogenética jerarquiza a las áreas para prioridades de conservación de biodiversidad con base en información codificada en filogenias (cladogramas), La meta de estas cate- gorías de conservación requiere tomar en consideración tantos factores que proporcionan información adi- cional (riqueza de taxones, patrones de distribución de los taxones, endemicidad del área y complementa- riedad entre áreas) como sea posible. Actualmente hay muchas medidas que consideran información filogenética (basadas en nodos, distancia genética y basadas en características). Diseñamos un índice filo- genético modificado basado en nodos que denominamos “peso estandarizado de endemicidad taxonómica”, el cual considera no solo la peculiaridad genética de los taxa que habitan una región determinada sino tam- bién su endemicidad. Una vez que el peso estandarizado de endemicidad identifica el área de mayor prior- idad, la complementariedad se puede usar para identificar la segunda área y así sucesivamente. Utilizamos este índice basado en nodos para jerarquizar áreas prioritarias para conservación en el sur de América del ‡email posadas@museo.fcnym.unlp.edu.ar Paper submitted September 1, 1999; revised manuscript accepted September 26, 2000.