Research: Addressing poor statistical support for wolf control and maternal penning as conservation measures for endangered mountain caribou

A new study shows that while addressing potential threats from wolves does not seem to be effective, an important new signal has emerged from the data: ecotype.

A wolf walks across the beach in the early morning light, with figure 1 in the foreground.

Photo by Ian Harland.

A new study demonstrates that addressing potential threats from wolves has not slowed the decline of mountain caribou in British Columbia and Alberta.

The scientists looked closely at the data provided in a previous study that examined how 18 caribou populations responded to different treatments including wolf culls, maternal penning, moose reduction, and combinations thereof, as well as controls. There were important errors in the statistical methods associated with that prior study.

“Worse than tax-funded programs to kill wolves in error, is the free pass that such an ill-advised diversion granted to industry, which continued to aggressively destroy habitat.”

Chris Darimont, Science Director, Raincoast Chair in Applied Conservation Science, University of Victoria

Using a standard but previously neglected statistical step, the new research arrived at strikingly different conclusions: a statistical model that examined the possibility that no treatments were effective performed just as well as the treatment model.  Accordingly, previous claims for strong support of the efficacy of wolf control are now in serious doubt.  The open access paper was published in the international peer-reviewed journal, Biodiversity and Conservation, by scientists from Raincoast Conservation Foundation and the Universities of Alberta, British Columbia, and Victoria.

Digging deeper into the data, the authors additionally found an important new signal. Not linked to any management action, population changes in caribou were instead associated with the four different ecotypes (or forms) of caribou. Of these, the southernmost “Deep-Snow mountain caribou,” found from Wells Gray Park into the Kootenays, experienced among the steepest declines. 

“Intact forests provide caribou with important lichens as food, as well as refuge from wolves and separation from other prey animals, including elk, moose, and deer. Without them, caribou must constantly be on the move to find food, exposing them on all sides. Predators are just one of the hazards.” – Lee Harding, retired Canadian Wildlife Service biologist, lead author

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Citation

Harding, L.E., Bourbonnais, M., Cook, A.T. et al. No statistical support for wolf control and maternal penning as conservation measures for endangered mountain caribou. Biodivers Conserv (2020). https://doi.org/10.1007/s10531-020-02008-3

Abstract

Mountain caribou, a behaviourally and genetically distinct set of ecotypes of the Woodland caribou (Rangifer tarandus caribou) restricted to the mountains of western Canada, have undergone severe population declines in recent decades. Although a broad consensus exists that the ultimate driver of these declines has been the reduction of habitat upon which mountain caribou depend, research and policy attention has increasingly focused on predation. Recently, Serrouya et al. (Proc Nat Acad Sci USA 116:6181–6186, 2019) analysed population dynamics data from 18 subpopulations in British Columbia and Alberta, Canada, subject to different treatments and ‘controls’, and concluded that lethal wolf control and maternal caribou penning provide the most effective ways to stabilize population declines. Here we show that this inference was based on an unbalanced analytical approach that omitted a null scenario, excluded potentially confounding variables and employed irreproducible habitat alteration metrics. Our reanalysis of available data shows that ecotype identity is a better predictor of population trends than any adaptive management treatments considered by Serrouya et al. Disparate behavioural characteristics and responses to industrial disturbance among ecotypes suggest it may be incorrect to assume that adaptive management strategies that might benefit one ecotype are transferable to another.

Select figures

Figure 1

Figure 1 from a study by Lee Harding and Chris Darimont showing poor statistical support for wolf control and maternal penning as conservation measures for endangered mountain caribou.
Variation in Δ𝑟 [log(𝜆𝑒𝑛𝑑) – log(𝜆𝑠𝑡𝑎𝑟𝑡)] across ecotypes. Filled circles overlaying boxplots have a horizontal jitter and show lambda for individual populations within each treatment. Capital letters indicate the results of a pairwise t-test with a Bonferroni correction, with different letters indicating significant differences. The Boreal ecotype was excluded from the test due to insufficient sample size.

Affiliations

  1. Department of Earth, Environmental and Geographic Sciences, University of British Columbia Okanagan
  2. Department of Biological Sciences CW405, University of Alberta
  3. Department of Geography, University of Victoria
  4. Raincoast Conservation Foundation

Despite warnings that industrial resource extraction, primarily forestry, was detrimental to maintaining viable caribou populations, habitat modification, fragmentation and associated road-building increased over subsequent decades. By the early 2000s, population declines had accelerated across the Canadian mountain caribou ecotypes, with Deep-Snow Mountain caribou registering a reduction of 45% in 27 years (COSEWIC 2014).

Lee E. Harding, et al., Biodiversity and Conservation (2020)