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Tree squirrel habitat selection and predispersal seed predation in a declining subalpine conifer

  • Plant-Animal interactions - Original Paper
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Abstract

Differential responses by species to modern perturbations in forest ecosystems may have undesirable impacts on plant-animal interactions. If such disruptions cause declines in a plant species without corresponding declines in a primary seed predator, the effects on the plant could be exacerbated. We examined one such interaction between Pinus albicaulis (whitebark pine), a bird-dispersed, subalpine forest species experiencing severe population declines in the northern part of its range, and Tamiasciurus hudsonicus (red squirrel), an efficient conifer seed predator, at 20 sites in two distinct ecosystems. Hypotheses about squirrel habitat preferences were tested to determine how changes in forest conditions influence habitat use and subsequent levels of predispersal cone predation. We performed habitat selection modeling and variable ranking based on Akaike’s information criterion; compared the level and variance of habitat use between two forest types (P. albicaulis dominant and mixed conifer); and modeled the relationship between P. albicaulis relative abundance and predispersal cone predation. T. hudsonicus did not demonstrate strong habitat preference for P. albicaulis, and thus, declines in the pine were not met with proportional declines in squirrel habitat use. P. albicaulis habitat variables were the least important in squirrel habitat selection. Squirrel habitat use was lower and varied more in P. albicaulis-dominant forests, and predispersal cone predation decreased linearly with increasing P. albicaulis relative abundance. In Northern Rocky Mountain sites, where P. albicaulis mortality was higher and abundance lower, squirrel predation was greater than in Central Rocky Mountain sites. In ecosystems with reduced P. albicaulis abundance, altered interactions between the squirrel and pine may lead to a lower proportion of P. albicaulis contributing to population recruitment because of reduced seed availability. Reducing the abundance of competing conifers will create suboptimal squirrel habitat, thus lowering cone predation in P. albicaulis and ensuring more seeds are available for avian dispersal.

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Acknowledgments

We thank R. Keane and W. McCaughey from the US Forest Service Rocky Mountain Research Station, K. Tonnessen from the Rocky Mountain Cooperative Ecosystem Studies Unit, and T. Carolin from Glacier National Park for financial assistance; S. Sweeney, J. Fothergill, B. Cook, and B. Stauffer for field assistance; D. Tomback, H. Zuuring, A. Sala, and two anonymous reviewers for thoughtful manuscript reviews; and E. Crone and H. Zuuring for analysis consultations. Funding was provided by a US Department of Interior Cooperative Conservation Initiative grant (CA 1200-99-007), a US Forest Service Research Joint Venture Agreement (05-JV-11221648-156), a US Department of Agriculture McIntire-Stennis Research Program grant, a US National Park Service fellowship, and the College of Forestry and Conservation, University of Montana. This work was carried out in accordance with the laws of the United States of America.

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  1. Shawn T. McKinney

    Present address: National Park Service Inventory and Monitoring Program, Sierra Nevada Network, P.O. Box 700-W, El Portal, CA, 95318, USA

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  1. College of Forestry and Conservation, University of Montana, Missoula, MT, 59812, USA

    Shawn T. McKinney & Carl E. Fiedler

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  1. Shawn T. McKinney
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Correspondence to Shawn T. McKinney.

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Communicated by Jörg Ganzhorn.

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McKinney, S.T., Fiedler, C.E. Tree squirrel habitat selection and predispersal seed predation in a declining subalpine conifer. Oecologia 162, 697–707 (2010). https://doi.org/10.1007/s00442-009-1496-5

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