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Ellison Abstract- 2002 Gotelli and Ellison 2002b

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Gotelli, N. J. & A. M. Ellison. 2002. Nitrogen deposition and extinction risk in the northern pitcher plant Sarracenia purpurea. Ecology 83: 2758-2765.


Chronic nitrogen deposition may affect the long-term survival of plant populations. The northern pitcher plant Sarracenia purpurea is a model system for forecasting extinction risk in the face of increasing nitrogen deposition. Uptake of nitrogen occurs directly from pitcher leaves, which fill with rainwater and prey, and accumulate nutrients. We monitored the demography of two populations of S. purpurea in ombrotrophic bogs of northern New England and described population growth with a four-stage matrix model. Growth, survivorship, and reproduction were in close balance, and the model predicted population growth rates close to zero, with long doubling times. In a life table response experiment, we manipulated in situ concentrations of nitrogen and phosphorus in pitcher plant leaves. At high levels of nitrogen and high nitrogen:phosphorus ratios, population growth rates were significantly depressed. Using local N deposition records, we forecast different nitrogen deposition scenarios and built a non-stationary population growth model, in which a different a transition matrix at each time step reflected the current deposition regime. Autocorrelation in the time series of nitrogen deposition rates generated periodic increases in population size superimposed on long-term trends of exponential decline. For a 1% annual increase in nitrogen deposition rates, this model predicted a substantial risk of extinction at 100 years (0.38 - 0.70), with an estimated population survival time of 160 to 180 years. Although slow-growing populations of Sarracenia can buffer substantial environmental change, chronic increases in nitrogen deposition rate threaten population persistence.

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