Long-term monitoring of cycles in Clethrionomys rutilus in the Yukon boreal forest

Baseline studies of small rodent populations in undisturbed ecosystems are rare.We report here 50 years of mon-itoring and experimentation in Yukon of a dominant rodent species in the North American boreal forest,the red-backed vole Clethrionomys rutilus.These voles breed in summer,weigh 20–25 g,and reach a maximum density of 20 to 25 per ha.Their populations have shown consistent 3–4-year cycles for the last 50 years with the only change being that peak densities averaged 8/ha until 2000 and 18/ha since that year.During the last 25 years,we have measured food resources,predator numbers,and winter weather,and for 1-year social interactions,to estimate their contribution to changes in the rate of summer increase and the rate of overwinter decline.All these potential limiting factors could contribute to changes in density,and we measured their relative contributions statistically with multiple regressions.The rate of winter decline in density was related to both food supply and winter severity.The rate of summer increase was related to summer berry crops and white spruce cone production.No measure of predator numbers was related to winter or summer changes in vole abundance.There was a large signal of climate change effects in these populations.There is no density dependence in summer population growth and only a weak one in winter population declines.None of our results provide a clear understanding of what generates 3–4-year cycles in these voles,and the major missing piece may be an understanding of social interactions at high density.

Impact of climate change on the small mammal community of the Yukon boreal forest

Long-term monitoring is critical to determine the stability and sustainability of wildlife populations,and if change has occurred,why.We have followed population density changes in the small mammal community in the boreal forest of the southern Yukon for 46 years with density estimates by live trapping on 3-5 unmanipulat­ed grids in spring and autumn.This community consists of 10 species and was responsible for 9%of the ener­gy flow in the herbivore component of this ecosystem from 1986 to 1996,but this increased to 38%from 2003 to 2014.Small mammals,although small in size,are large in the transfer of energy from plants to predators and decomposers.Four species form the bulk of the biomass.There was a shift in the dominant species from the 1970s to the 2000s,with Myodes rutilus increasing in relative abundance by 22%and Peromyscus maniculatus decreasing by 22%.From 2007 to 2018,Myodes comprised 63%of the catch,Peromyscus 20%,and Microtus species 17%.Possible causes of these changes involve climate change,which is increasing primary production in this boreal forest,and an associated increase in the abundance of 3 rodent predators,marten(Martes ameri­cana),ermine(Mustela ermine)and coyotes(Canis latrans).Following and understanding these and potential future changes will require long-term monitoring studies on a large scale to measure metapopulation dynamics.The small mammal community in northern Canada is being affected by climate change and cannot remain sta­ble.Changes will be critically dependent on food-web interactions that are species-specific.

Impact of rewilding,species introductions and climate change on the structure and function of the Yukon boreal forest ecosystem

Community and ecosystem changes are happening in the pristine boreal forest ecosystem of the Yukon for 2 reasons.First,climate change is affecting the abiotic environment(temperature,rainfall and growing season)and driving changes in plant productivity and predator-prey interactions.Second,simultaneously change is occurring because of mammal species reintroductions and rewilding.The key ecological question is the impact these faunal changes will have on trophic dynamics.Primary productivity in the boreal forest is increasing because of climatic warming,but plant species composition is unlikely to change significantly during the next 50-100 years.The 9-10-year population cycle of snowshoe hares will persist but could be reduced in amplitude if winter weather increases predator hunting efficiency.Small rodents have increased in abundance because of increased vegetation growth.Arctic ground squirrels have disappeared from the forest because of increased predator hunting efficiency associated with shrub growth.Reintroductions have occurred for 2 reasons:human reintroductions of large ungulates and natural recolonization of mammals and birds extending their geographic ranges.The deliberate rewilding of wood bison(Bison bison)and elk(Cervus canadensis)has changed the trophic structure of this boreal ecosystem very little.The natural range expansion of mountain lions(Puma concolor),mule deer(Odocoileus hemionus)and American marten(Martes americana)should have few ecosystem effects.Understanding potential changes will require long-term monitoring studies and experiments on a scale we rarely deem possible.Ecosystems affected by climate change,species reintroductions and human alteration of habitats cannot remain stable and changes will be critically dependent on food web interactions.