Assessing Status and Trends of Threatened Species from Uncertain Monitoring Data

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Software: RAMAS/GIS, 

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Funding:National Science Foundation.

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Presented/published at: Expanded summary of the presentation at the 2004 Annual Meeting of the Society for Conservation Biology (Saturday, July 31, 4:00 pm)

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Authors: H. Resit Akçakaya, David Myers

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Location of study: Applied Biomathematics, Setauket, NY

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Range (spatial distribution) and population trends (temporal dynamics) are two important attributes of a species, and are used in most assessments of species status, including the U.S. Endangered Species Act, the IUCN criteria, and NatureServe's Heritage Status criteria. Measures of spatial distribution include extent of occurrence (EOO; or range size), and area of occupancy (AOO, or occupied habitat). Measures of temporal trend include past, current, and expected future population declines, usually calculated over 1 to 3 generations.

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These measures of spatial distribution and temporal trend are often known with large uncertainties. The causes of these uncertainties include observations with different levels of reliability (e.g., because they are old or unconfirmed),

observation locations that are uncertain discontinuities in the distribution, and to what extend they should be excluded from the calculation of EOO inconsistencies in the resolution and position of the measurement grid (for AOO); censuses with different sample sizes and/or reliabilities uncertainty in generation length.

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We are developing methods to address these uncertainties, and to estimate these three measures as uncertain quantities. These methods include using alpha-hulls (a generalization of convex hulls or minimum convex polygons) to calculate EOO, finding minimum and maximum possible polygons and grid counts based on location uncertainty and grid registration uncertainty, using scale-area curves for estimating AOO for a standard reference grid size, and performing fuzzy regression (including least squares and parameter-bounding methods) for estimating the range of population trends.

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