Threatened Species and the Potential Loss of Phylogenetic Diversity: Conservation Scenarios Based on Estimated Extinction Probabilities and Phylogenetic Risk Analysis

摘要

New species conservation strategies, including the EDGE of Existence (EDGE) program, have expanded threatened species assessments by integrating information about species' phylogenetic distinctiveness. Distinctiveness has been measured through simple scores that assign shared credit among species for evolutionary heritage represented by the deeper phylogenetic branches. A species with a high score combined with a high extinction probability receives high priority for conservation efforts. Simple hypothetical scenarios for phylogenetic trees and extinction probabilities demonstrate how such scoring approaches can provide inefficient priorities for conservation. An existing probabilistic framework derived from the phylogenetic diversity measure (PD) properly captures the idea of shared responsibility for the persistence of evolutionary history. It avoids static scores, takes into account the status of close relatives through their extinction probabilities, and allows for the necessary updating of priorities in light of changes in species threat status. A hypothetical phylogenetic tree illustrates how changes in extinction probabilities of one or more species translate into changes in expected PD. The probabilistic PD framework provided a range of strategies that moved beyond expected PD to better consider worst-case PD losses. In another example, risk aversion gave higher priority to a conservation program that provided a smaller, but less risky, gain in expected PD. The EDGE program could continue to promote a list of top species conservation priorities through application of probabilistic PD and simple estimates of current extinction probability. The list might be a dynamic one, with all the priority scores updated as extinction probabilities change. Results of recent studies suggest that estimation of extinction probabilities derived from the red list criteria linked to changes in species range sizes may provide estimated probabilities for many different species. Probabilistic PD provides a framework for single-species assessment that is well-integrated with a broader measurement of impacts on PD owing to climate change and other factors.Las nuevas estrategias de conservacion, incluyendo el programa EDGE of Existence (EDGE), han expandido las evaluaciones de especies amenazadas mediante la integracion de informacion sobre la unicidad filogenetica de las especies. La unicidad se ha medido por medio de calificaciones simples que asignan credito compartido entre especies por herencia evolutiva representada por las ramas filogeneticas mas profundas. Una especie con una calificacion alta combinada con una alta probabilidad de extincion recibe prioridad alta para los esfuerzos de conservacion. Los escenarios hipoteticos simples para arboles filogeneticos y probabilidades de extincion demuestran que esos metodos de calificacion pueden proporcionar prioridades de conservacion ineficientes. Un marco de referencia probabilistico existente derivado de la medida de diversidad filogenetica (PD) captura apropiadamente la idea de responsabilidad compartida para la persistencia de la historia evolutiva. Evita calificaciones estaticas, y permite la actualizacion de prioridades necesaria a la luz de cambios en el estatus de amenaza de la especie. Un arbol filogenetico hipotetico ilustra como los cambios en las probabilidades de extincion de una o mas especies se traducen en cambios en la PD esperada. El marco de referencia probabilistico de la PD proporciono una gama de estrategias que se movio mas alla de la PD esperada para considerar los peores cass de perdidas de PD. En otro ejemplo, la aversion de riesgo dio mayor prioridad a un programa de conservacion que proporciono una ganancia pequena, pero menos riesgosa, en la PD esperada. El programa EDGE podria seguir promoviendo una lista de prioridades de conservacion de especies mediante la aplicacion de PD probabilistica y estimaciones sencillas de la probabilidad de extincion actual. Sin emb