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Modeling future range expansion and management strategies for an invasive squirrel species

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Abstract

Successful management of an invasive species requires in depth knowledge of the invader, the invaded ecosystem, and their interactions. The complexity of the species-system interactions can be reduced and represented in ecological models for better comprehension. In this study, a spatially explicit population model was created using the RAMAS software package to simulate the past and future invasion dynamics of the eastern grey squirrel (Sciurus carolinensis) in the fragmented habitat in case study areas in Ireland. This invasive squirrel species causes economic damage by bark stripping forest crops and is associated with the decline of its native congener (S. vulgaris). Three combinations of demographic and dispersal parameters, which best matched the distribution of the species shortly after introduction, were used to simulate invasion dynamics. Future population expansion was modeled under scenarios of no control and two different management strategies: fatal culls and immunocontraceptive vaccination programmes. In the absence of control, the grey squirrel range is predicted to expand to the south and southwest of Ireland endangering internationally important habitats, vulnerable forest crops, and the native red squirrel. The model revealed that region-wide intensive and coordinated culls would have the greatest impact on grey squirrel populations. Control strategies consisting solely of immunocontraceptive vaccines, often preferred by public interest groups, are predicted to be less effective. Complete eradication of the grey squirrel from Ireland is not economically feasible and strategic evidence-based management is required to limit further range expansion. Ecological models can be used to choose between informed management strategies based on predicted outcomes.

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Acknowledgments

We thank HR Akçakaya and WT Root for advice on the operation of RAMAS GIS 6.0 and S Warner for assistance with map raster design and JL Koprowski for further support. We also thank ML Guichón for advice on extracting relevant information from model outputs. We greatly appreciate the constructive comments of two anonymous reviewers on an earlier version of the manuscript. EAG was funded by the Irish Research Council and additional funding to CL was provided by the Department of Agriculture, Food and the Marine of the Irish Government under the National Development Plan 2007–2013.

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Correspondence to Emily A. Goldstein.

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Goldstein, E.A., Butler, F. & Lawton, C. Modeling future range expansion and management strategies for an invasive squirrel species. Biol Invasions 18, 1431–1450 (2016). https://doi.org/10.1007/s10530-016-1092-7

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