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      Predator–prey dynamics of bald eagles and glaucous‐winged gulls at Protection Island, Washington, USA

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          Abstract

          1. Bald eagle ( Haliaeetus leucocephalus) populations in North America rebounded in the latter part of the twentieth century, the result of tightened protection and outlawing of pesticides such as DDT. An unintended consequence of recovery may be a negative impact on seabirds. During the 1980s, few bald eagles disturbed a large glaucous‐winged gull ( Larus glaucescens) colony on Protection Island, Washington, USA, in the Salish Sea. Breeding gull numbers in this colony rose nearly 50% during the 1980s and early 1990s. Beginning in the 1990s, a dramatic increase in bald eagle activity ensued within the colony, after which began a significant decline in gull numbers.

          2. To examine whether trends in the gull colony could be explained by eagle activity, we fit a Lotka–Volterra‐type predator–prey model to gull nest count data and Washington State eagle territory data collected in most years between 1980 and 2016. Both species were assumed to grow logistically in the absence of the other.

          3. The model fits the data with generalized R 2 = 0.82, supporting the hypothesis that gull dynamics were due largely to eagle population dynamics.

          4. Point estimates of the model parameters indicated approach to stable coexistence. Within the 95% confidence intervals for the parameters, however, 11.0% of bootstrapped parameter vectors predicted gull colony extinction.

          5. Our results suggest that the effects of bald eagle activity on the dynamics of a large gull colony were explained by a predator–prey relationship that included the possibility of coexistence but also the possibility of gull colony extinction. This study serves as a cautionary exploration of the future, not only for gulls on Protection Island, but for other seabirds in the Salish Sea. Managers should monitor numbers of nests in seabird colonies as well as eagle activity within colonies to document trends that may lead to colony extinction.

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          Estimation of Growth and Extinction Parameters for Endangered Species

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            FITTING POPULATION MODELS INCORPORATING PROCESS NOISE AND OBSERVATION ERROR

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              POPULATION TIME SERIES: PROCESS VARIABILITY, OBSERVATION ERRORS, MISSING VALUES, LAGS, AND HIDDEN STATES

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                Author and article information

                Contributors
                henson@andrews.edu
                Journal
                Ecol Evol
                Ecol Evol
                10.1002/(ISSN)2045-7758
                ECE3
                Ecology and Evolution
                John Wiley and Sons Inc. (Hoboken )
                2045-7758
                11 March 2019
                April 2019
                : 9
                : 7 ( doiID: 10.1002/ece3.2019.9.issue-7 )
                : 3850-3867
                Affiliations
                [ 1 ] Department of Biology Andrews University Berrien Springs Michigan
                [ 2 ] Department of Mathematics Andrews University Berrien Springs Michigan
                [ 3 ] Department of Biological Sciences California State University Los Angeles California
                [ 4 ] Control and Dynamical Systems California Institute of Technology Pasadena California
                [ 5 ] Department of Computer Science and Mathematics Sul Ross State University Alpine Texas
                [ 6 ] Department of Biological Sciences Walla Walla University College Place Washington
                [ 7 ] Washington Department of Fish and Wildlife Olympia Washington
                Author notes
                [*] [* ] Correspondence

                Shandelle M. Henson, Department of Mathematics, Andrews University, Berrien Springs, MI.

                Email: henson@ 123456andrews.edu

                Article
                ECE35011
                10.1002/ece3.5011
                6468083
                3beeeda2-33a9-4445-9c13-c9e416eaa173
                © 2019 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.

                This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                Page count
                Figures: 10, Tables: 3, Pages: 18, Words: 12696
                Product
                Funding
                Funded by: U. S. National Science Foundation
                Funded by: Division of Mathematical Sciences
                Award ID: DMS‐1225529
                Award ID: DMS‐1407040
                Categories
                Original Research
                Original Research
                Custom metadata
                2.0
                ece35011
                April 2019
                Converter:WILEY_ML3GV2_TO_NLMPMC version:5.6.2.1 mode:remove_FC converted:16.04.2019

                Evolutionary Biology
                bald eagles,glaucous‐winged gulls,lotka–volterra model,predator–prey dynamics,protection island,salish sea

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