Predicting the Future: Wolverines and Climate Change

Mammalogists and conservation biologists are increasingly concerned about the impacts of climate change on distribution and abundance of threatened and endangered mammals. For example, recent changes in sea ice in the Arctic led Amstrup et al. (2010) to predict a loss of two-thirds of the world’s polar bear population by 2050 if action is not taken immediately. But what about the effects of shifting climate patterns on completely terrestrial species in the continental United States? Are there other mammal species that that rely on specific climate variables?

One such species is the wolverine (
Gulo gulo; Figure 1). Wolverines are known to have an obligate relationship with spring snow cover and summer temperatures. In other words, snow packs that remain into late spring are vital for den insulation and the successful weaning of pups. Likewise, when mean maximum summer temperatures exceed approximately 22oC, wolverines may have difficulty maintaining thermoneutrality (Copeland et al. 2010). If climate change drives spring and summer temperatures higher, we may see a decline or loss of suitable wolverine habitat in the United States.

wolverine
Figure 1. An adult wolverine (Gulo gulo). (From Flickr/Fiskfisk)

Using state of the art climate models,
Peacock (2011) plotted the likely changes in snow cover and summer temperatures in the western United States. These models are based on three estimates of CO2 emission (low, medium-low, and high emissions; Figure 2). The high emissions model assumes no direct action is taken by governments to curtail CO2 emissions. The low-medium emissions scenario assumes CO2 emissions remain at present levels until 2020, and then decline to
zero by 2080, which seems highly unlikely.

CO2levels
Figure 2. CO2 emission models used in Peacock 2011 to estimate snow cover and summer temperatures in 4 western states. (From Peacock 2011)


Peacock’s models show that by the year 2050 snow cover will be gone from traditional wolverine habitats by early spring or late winter (Figure 3). Likewise, these models predict that mean maximum August temperatures are likely to be well above 22
oC, with the result that wolverines will have difficulty tolerating the warmer summers within its current US range. Even under the more conservative medium-low emission scenarios (which require sharp reductions in emissions), the spring months are likely to be snow free in many years. As a result, wolverine populations are expected to decline in the western United States as wolverines retreat northward into Canada.


snowmap
Figure 3. Model projections of the percentage of days between 1 March and 15 May where the average snow cover exceeding 20 cm depth. (a) the decade from 1890–1899, (b) 1990–1999, (c) 2051–2059, and (d) 2090–2099. (From Peacock 2011)

This does not bode well for wolverines in the lower 48. As Peacock puts it, “Unless the wolverine is able to very rapidly adapt to summer-time temperatures far above anything it currently experiences, and to a spring with little or zero snow cover, it is unlikely that it will continue to survive in the contiguous US under a high or medium–low emissions scenario”.


References

Amstrup, S.C., DwWeaver, E.T., Douglas, D.C., Marcot, B.G., Durner, G.M., Bitz, C.M. and D.A. Bailey. (2010) Greenhouse gas mitigation can reduce sea-ice loss and increase polar bear persistence.
Nature, 468:955-958.

Copeland, J.P., et al. (2010) The bioclimatic envelope of the wolverine
(Gulo gulo): do climatic constraints limit its geographic
distribution?
Canadian Journal of Zoology, 88 233–46.

Peacock, S. (2011). Projected 21st century climate change for wolverine habitats within the contiguous United States Environmental Research Letters, 6 (1) DOI: 10.1088/1748-9326/6/1/014007