Population Viability Analysis for an Endangered Plant

: Demographic modeling is used to understand the population viability of Furbish's lousewort, Pedicularis furbishiae, a perennial plant species endemic to the St. John River Valley in northern Maine. Environment-specific summaries of demographic parameters (survivorship, growth, and fecundity) over four years, organized into stage-based projection matrices, provide predictions of future population dynamics given a deterministic extension of past conditions. Stochastic modeling, using (I) empirically observed variation in demographic parameters, and (2) estimated rates of natural catastrophes, leads to predictions of extinction probability. P. furbishiae viability has varied widely over the study period Viable populations with finite rates of increase > 1 are found where cover is low, woody plants do not dominate, and disturbance does not occur. Rates of increase vary over time, suggesting that stochastic analyses would be realistic. Stochastic measures of population viability incorporating environmental variation suggest that early successional environments, especially wetter sites, can support viable populations in the absence of disturbance. However; observed rates of natural catastrophe dominate viability estimates of individual populations. Metapopulation dynamics feature extinction rates that are greater than recolonization rates, and may be affected by land use in the watershed Species management needs to consider a large-scale view of the riverine corridor. Resumen: En este trabajo se emplea el modelaje demografico para esclarecer la viabilidad poblacional de la planta perenne Pedicularis furbishiae, (Furbish's lousewort), endemica al valle del rio St. John, en el norte del estado de Maine. Los resumenes de parametros demograficos, (sobrevivencia, crecimiento, y fecundidad), de un periodo de cuatro anos, especificos para cada tipo de ambiente, se organizaron en matrices de proyeccion por etapas, para predecir la futura dinamica poblacional en base a una extension deterministica de condiciones anteriores. Los modelos estocasticos, utilizando (1) variaciones en parametros demograficos observadas en la practica, y (2) indices estimados de catastrofes naturales, conducen a predicciones de probabiliaades de extincion. La viabilidad de P. furbishiae vario ampliamente durante el periodo de estudio. Se encuentran poblaciones viables (con lamda mayor a 1) en areas con poca cobertura donde no dominan las plantas lenosas y no existe alteracion. Las tasas de incremento varian con el tiempo, sugiriendo que los analisis estocaticos son realistas. Las medidas estocasticas de viabilidad poblacional que incorporan variaciones ambientales, sugieren que los ambientes en etapas de sucesion temprana, especialmente en los sitios mas humedos, podrian sostener poblaciones viables, si es que no existe alteracion, Sin embargo, las estimaciones de viabilidad para poblaciones individuales, estan dominadas por los porcentajes de catastrofes naturales. La dinamica de metapoblaciones presenta indices de extincion mayores que los indices de recolonizacion, y podrian ser afectades por el uso de tierras en las areas de las cuencas hidrograficas correspondientes. El manejo de especies necesita considerar elpanorama a escala mayor del corredor fluvial.

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