Population viability analysis (PVA) has become a commonly used tool in endangered species management. There is no single process that constitutes PVA, but all approaches have in common an assessment of a population's risk of extinction (or quasi extinction) or its projected population growth either under current conditions or expected from proposed management. As model sophistication increases, and software programs that facilitate PVA without the need for modeling expertise become more available, there is greater potential for the misuse of models and increased confusion over interpreting their results. Consequently, we discuss the practical use and limitations of PVA in conservation planning, and we discuss some emerging issues of PVA. We review extant issues that have become prominent in PVA, including spatially explicit modeling, sensitivity analysis, incorporating genetics into PVA, PVA in plants, and PVA software packages, but our coverage of emerging issues is not comprehensive. We conclude that PVA is a powerful tool in conservation biology for comparing alternative research plans and relative extinction risks among species, but we suggest caution in its use: (1) because PVA is a model, its validity depends on the appropriateness of the model's structure and data quality; (2) results should be presented with appropriate assessment of confidence; (3) model construction and results should be subject to external review, and (4) model structure, input, and results should be treated as hypotheses to be tested. We also suggest (5) restricting the definition of PVA to development of a formal quantitative model, (6) focusing more research on determining how pervasive densitydependence feedback is across species, and (7) not using PVA to determine minimum population size or (8) the specific probability of reaching extinction. The most appropriate use of PVA may be for comparing the relative effects of potential management actions on population growth or persistence. Uso y Temas Emergentes del Análisis de Viabilidad PoblacionalResumen: El análisis de viabilidad poblacional (AVP) es una herramienta de uso común en el manejo de especies en peligro. No hay un proceso único que constituya al AVP, pero todos los enfoques tienen en común la estimación del riesgo de extinción (o cuasi extinción) o la proyección del crecimiento poblacional, ya sea bajo las condiciones actuales o las esperadas del manejo propuesto. A medida que aumenta la sofisticación del modelo, y que se dispone de programas de cómputo que facilitan el AVP sin necesidad de experiencia en modelaje, hay una mayor posibilidad de desaprovechar el modelo y una mayor confusión en la interpretación de los resultados. En consecuencia, discutimos el uso práctico y las limitaciones del AVP en la planificación de conservación y discutimos algunos temas emergentes del AVP. Revisamos temas vigentes que son prominentes en el AVP, incluyendo el modelaje espacialmente explícito, el análisis de sensibilidad, la inclusión de la genética en el AVP, AVP en plantas y paquetes...

Conservation genetics utilizes the tools and concepts of genetics and applies them to problems in conservation biology. For example, molecular genetic techniques, such as protein electrophoresis, and analysis of mitochondrial DNA and highly variable nuclear genes (including DNA fingerprinting), have been important in documenting the extent and pattern of genetic variation in endangered species. We review these techniques and their advantages and disadvantages, and give examples of their application to endangered species. For captive animal populations, pedigree analysis has become the basic approach to evaluate breeding priority of particular individuals. Several pedigree analysis techniques are commonly used, but peeling and gene dropping give the most information. We compared these techniques and illustrate their value with applications to the Guam Rail, Przewalski's horse, and other endangered captive animals. The rationale for much conservation genetic interpretation is base in evolutionary genetics. We discuss the avoidance of inbreeding depression and the maintenance of genetic variation-both primary conservation genetic goals-from this perspective. In addition, we suggest aspects of these factors that deserve greater attention in their overall application to conservation planning. Finally, we briefly mention three evolutionary topics-the relationship of heterozygosity and fitness, population bottlenecks, and outbreeding depression-that have implications for conservation genetics. Although simple interpretation in these areas is appealing, we feel that because they are only generally understood and often quite controversial, their application to endangered-species management should be carefully evaluated and monitored.

The Speke's gazelle (Gazella spekei) captive breeding program has been presented as one of the few examples of selection reducing the genetic load of a population and as a potential model for the captive breeding of endangered species founded from a small number of individuals. In this breeding program, three generations of mate selection apparently increased the viability of inbred individuals. We reanalyzed the Speke's gazelle studbook and examined potential causes for the reduction of inbreeding depression. Our analysis indicates that the decrease in inbreeding depression is not consistent with any model of genetic improvement in the herd. Instead, we found that the effect of inbreeding decreased from severe to moderate during the first generation of inbreeding, and that this change is responsible for almost all of the decline in inbreeding depression observed during the breeding program. This eliminates selection as a potential explanation for the decrease in inbreeding depression and suggests that inbreeding depression may be more sensitive to environmental influences than is usually thought.

Large populations of free-roaming cats (FRCs) generate ongoing concerns for welfare of both individual animals and populations, for human public health, for viability of native wildlife populations, and for local ecological damage. Managing FRC populations is a complex task, without universal agreement on best practices. Previous analyses that use simulation modeling tools to evaluate alternative management methods have focused on relative efficacy of removal (or trap-return, TR), typically involving euthanasia, and sterilization (or trap-neuter-return, TNR) in demographically isolated populations. We used a stochastic demographic simulation approach to evaluate removal, permanent sterilization, and two postulated methods of temporary contraception for FRC population management. Our models include demographic connectivity to neighboring untreated cat populations through natural dispersal in a metapopulation context across urban and rural landscapes, and also feature abandonment of owned animals. Within population type, a given implementation rate of the TR strategy results in the most rapid rate of population decline and (when populations are isolated) the highest probability of population elimination, followed in order of decreasing efficacy by equivalent rates of implementation of TNR and temporary contraception. Even low levels of demographic connectivity significantly reduce the effectiveness of any management intervention, and continued abandonment is similarly problematic. This is the first demographic simulation analysis to consider the use of temporary contraception and account for the realities of FRC dispersal and owned cat abandonment.