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Quantifying the importance of geographic replication and representativeness when estimating demographic rates, using a coastal species as a case study

Authors

  • Christopher R. Field,

    1. Department of Ecology, Evolutionary Biology and Center for Conservation and Biodiversity, University of Connecticut, 75 North Eagleville Road, U-43, Storrs, Connecticut 06269, USA
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  • Katharine J. Ruskin,

    1. School of Biology and Ecology, Climate Change Institute, University of Maine, 200 Clapp Greenhouse, Orono, Maine 04469, USA
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  • Bri Benvenuti,

    1. Department of Natural Resources and the Environment, University of New Hampshire, 46 College Road, Durham, New Hampshire 03824, USA
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  • Alyssa C. Borowske,

    1. Department of Ecology, Evolutionary Biology and Center for Conservation and Biodiversity, University of Connecticut, 75 North Eagleville Road, U-43, Storrs, Connecticut 06269, USA
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  • Jonathan B. Cohen,

    1. Department of Environmental and Forest Biology, State University of New York College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY 13210, USA
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  • Laura Garey,

    1. School of Biology and Ecology, Climate Change Institute, University of Maine, 200 Clapp Greenhouse, Orono, Maine 04469, USA
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  • Thomas P. Hodgman,

    1. Bird Group, Maine Dept. of Inland Fisheries and Wildlife, 650 State Street, Bangor, Maine 04401, USA
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  • Rebecca A. Kern,

    1. Department of Entomology and Wildlife Ecology, University of Delaware, 257 Townsend Hall, Newark, DE 19716, USA
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  • Erin King,

    1. U.S. Fish and Wildlife Service, Region 5 Division of Natural Resources, Stewart B. McKinney NWR, 733 Old Clinton Road, Westbrook, CT 06498, USA
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  • Alison R. Kocek,

    1. Department of Environmental and Forest Biology, State University of New York College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY 13210, USA
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  • Adrienne I. Kovach,

    1. Department of Natural Resources and the Environment, University of New Hampshire, 46 College Road, Durham, New Hampshire 03824, USA
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  • Kathleen M. O'Brien,

    1. U.S. Fish and Wildlife Service, Rachel Carson National Wildlife Refuge, 321 Port Road, Wells, ME 04090, USA
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  • Brian J. Olsen,

    1. School of Biology and Ecology, Climate Change Institute, University of Maine, 200 Clapp Greenhouse, Orono, Maine 04469, USA
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  • Nancy Pau,

    1. U.S. Fish and Wildlife Service, Parker River National Wildlife Refuge, 6 Plum Island Turnpike, Newburyport, MA 01950, USA
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  • Samuel G. Roberts,

    1. Department of Entomology and Wildlife Ecology, University of Delaware, 257 Townsend Hall, Newark, DE 19716, USA
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  • Emma Shelly,

    1. Department of Ecology, Evolutionary Biology and Center for Conservation and Biodiversity, University of Connecticut, 75 North Eagleville Road, U-43, Storrs, Connecticut 06269, USA
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  • W. Gregory Shriver,

    1. Department of Entomology and Wildlife Ecology, University of Delaware, 257 Townsend Hall, Newark, DE 19716, USA
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  • Jennifer Walsh,

    1. Department of Natural Resources and the Environment, University of New Hampshire, 46 College Road, Durham, New Hampshire 03824, USA
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  • Chris S. Elphick

    1. Department of Ecology, Evolutionary Biology and Center for Conservation and Biodiversity, University of Connecticut, 75 North Eagleville Road, U-43, Storrs, Connecticut 06269, USA
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  • This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: [10.1111/ecog.02424].

Corresponding author: Christopher R. Field, Department of Ecology & Evolutionary Biology and Center for Conservation and Biodiversity, University of Connecticut, 75 North Eagleville Road, U-43, Storrs, Connecticut 06269, USA. E-mail: christopher.field@uconn.edu

Abstract

Demographic rates are rarely estimated over an entire species range, limiting empirical tests of ecological patterns and theories, and raising questions about the representativeness of studies that use data from a small part of a range. The uncertainty that results from using demographic rates from just a few sites is especially pervasive in population projections, which are critical for a wide range of questions in ecology and conservation. We developed a simple simulation to quantify how this lack of geographic representativeness can affect inferences about the global mean and variance of growth rates, which has implications for the robust design of a wide range of population studies. Using a coastal songbird, saltmarsh sparrow (Ammodramus caudacutus), as a case study, we first estimated survival, fecundity, and population growth rates at 21 sites distributed across much of their breeding range. We then subsampled this large, representative dataset according to five sampling scenarios in order to simulate a variety of geographic biases in study design. We found spatial variation in demographic rates, but no large systematic patterns. Estimating the global mean and variance of growth rates using subsets of the data suggested that at least 10-15 sites were required for reasonably unbiased estimates, highlighting how relying on demographic data from just a few sites can lead to biased results when extrapolating across a species range. Sampling at the full 21 sites, however, offered diminishing returns, raising the possibility that for some species accepting some geographical bias in sampling can still allow for robust range-wide inferences. The sub-sampling approach presented here, while conceptually simple, could be used with both new and existing data to encourage efficiency in the design of long-term or large-scale ecological studies.

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