Demographic responses of boreal caribou to cumulative disturbances highlight elasticity of range-specific tolerance thresholds

Abstract

Conserving species-at-risk requires quantifiable knowledge of the key drivers of population change. Non-linear demographic responses to habitat loss have been documented for many species and may serve to establish quantitative habitat thresholds for management purposes. In Canada, boreal populations of woodland caribou are considered threatened; Environment Canada’s empirical model of calf recruitment–range disturbance suggests that at least 65% undisturbed habitat is required to ensure viability. We tested the relationship upon which this conservation guideline is based by pairing demographic estimates with range conditions over a 10-year period for three boreal caribou populations. Our objectives were (1) to evaluate evidence of intra-population demographic responses to fluctuations in range quality over time; (2) to evaluate inter-population differences in demographic responses to cumulative range disturbances; and (3) to evaluate the sensitivity of disturbance tolerance thresholds to variation in local population demography. We found strong evidence in support of the disturbance–recruitment relationship for within-population responses over time (R2 = 0.77). Mixed effects logistic regression modeling revealed variations in local population responses to cumulative habitat depletion. Range-specific disturbance thresholds derived from Monte Carlo simulations were highly elastic in response to observed variation in local population demography, suggesting that 65% undisturbed habitat is insufficient when adult female survival and/or sex ratio is suboptimal. Study populations were determined to be not self-sustaining (Pr(λ ≥ 0.99) = 37–47%). Adult survival was comparable to estimates reported elsewhere despite Aboriginal harvesting for subsistence purposes. Results underscored potential trade-offs between forest harvesting and wildlife habitat conservation. Protection and restoration of sufficient quantities of undisturbed habitat, particularly via road reclamation, is essential for caribou population recovery.

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Acknowledgements

We wish to thank I. Schmelzer and M. Festa-Bianchet for suggesting constructive improvements to a previous version of this manuscript. Thanks to G. Hétu, S. Rivard, L. Lambert, C. Jutras and F. Manka for their scientific and logistical support coordinating the caribou telemetry surveys and datasets, to M.J. Mazerolle for his assistance with statistical analyses, and M. Desrochers for GIS support. This project was funded by the Ministère des Forêts, de la Faune et des Parcs du Québec (MFFP) to support the work of a regional task force in collaboration with the Cree Nation Government.

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Correspondence to Martin-Hugues St-Laurent.

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Communicated by Karen E. Hodges.

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Rudolph, T.D., Drapeau, P., Imbeau, L. et al. Demographic responses of boreal caribou to cumulative disturbances highlight elasticity of range-specific tolerance thresholds. Biodivers Conserv 26, 1179–1198 (2017). https://doi.org/10.1007/s10531-017-1292-1

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Keywords

  • Boreal caribou
  • Canadian boreal forest
  • Cumulative disturbances
  • Demographic modeling
  • Disturbance thresholds
  • Long-term monitoring