1. More than 75 years have passed since W.C. Allee proposed that breakdowns in sociality may shift animal populations to inverse density dependence at small sizes and thereby hasten spirals to extinction. Despite decades of attention, empirical evidence of this 'Allee effect' in wild populations remains scarce. 2. Here, we report on findings from a multi-year study of the population ecology and behaviour of the critically endangered Vancouver Island marmot (Marmota vancouverensis) and present quantitative evidence of an Allee effect and highlight the mechanisms that drive it. 3. The V.I. marmot is a large, social rodent endemic to Vancouver Island, Canada, and its population has declined by 80-90% since the 1980s. The species currently is represented in the wild by roughly 200 individuals. 4. This study compared characteristics of contemporary V.I. marmots (2002-2005) with (i) animals in the same population at an earlier time period (1973-1975) and (ii) congeners. Specifically, data on time allocation, social activity and ranging behaviour of animals in colonies in the late stages of decline were compared with historical data collected from colonies under more stable demographic conditions. 5. We found that contemporary V.I. marmots had home ranges that were 10-60x larger than historic animals and congeners, interacted with conspecifics at 10% of the historic rate, devoted 10x more time to anti-predator vigilance, and abandoned the bi-modal activity patterns previously described for this and other marmot species. Contemporary marmots also showed an 86% decline in feeding rate, and entered hibernation on average 20 days later than animals in historic populations. 6. Combined with results showing reduced per capita survival and reproduction in contemporary marmots, these findings suggest a strong role for Allee effects in the current plight of the Vancouver Island marmot. A positive link between aspects of fitness and population size emphasizes the need to identify threshold colony sizes and densities necessary to promote recovery. We discuss this and other implications of this species' social 'meltdown'.

Context The arctic ground squirrel (Urocitellus parryii) comprised 17% of the biomass of herbivores in the Yukon boreal forest during the summer months from 1987 to 1996 and was responsible for 23% of the energy flow at the herbivore level. By 2000, ground squirrel populations in this region collapsed to nearly zero and have remained there. Aims We summarise the population monitoring (since 1975) and recent experimental work that has been done on this key herbivore in the Kluane area of the southern Yukon to test one mechanistic hypothesis as the possible explanation for this population collapse and subsequent lack of recovery: predation. Methods Ground squirrels are the preferred summer prey of bird and mammal predators when snowshoe hare (Lepus americanus) populations are declining. We used translocations into formerly occupied habitat and radiotelemetry to determine movements and causes of death from 2009 to 2014. We surveyed 158 sites between 2008 and 2013 to measure the disappearance of colonies in alpine and forest habitats over 25 000 km2. Key results Ground squirrels from 2000 to 2013 comprised a small fraction of the herbivore biomass in the boreal forest zone, down from 17% earlier. Most forest populations (~95%) are currently extinct, whereas just over half (65%) of low-elevation meadow populations are locally extinct. One hypothesis is that ground squirrels in the forest have been driven into a predator pit from which they cannot recover. They remain abundant in alpine tundra (93% occupancy rate) and around airport runways and human habitations (97% occupancy), but there is no apparent dispersal from alpine areas down into the boreal forest. Conclusion The predator pit hypothesis is a likely explanation for the initial collapse and sustained decline in population size from 2000 to 2013. Recent attenuation of the hare cycle and milder winter climate have allowed shrubs to expand throughout the forest, thereby reducing visibility and increasing predation risk. This conclusion will be tested in further research using reintroductions to formerly occupied sites. Implication If the loss of this herbivore from the boreal forest is not reversed, predator pressure on the other major herbivores of the montane forest zone is likely to change significantly.

The Interior Wetbelt (IWB) of British Columbia, which includes the globally rare Inland Temperate Rainforest (ITR), contains primary forests poorly attributed and neglected in conservation planning. We evaluated the IWB and ITR using four IUCN Red List of Ecosystems Criteria: geographic distribution, environmental degradation (abiotic and biotic factors), and likelihood of ecosystem collapse. Clearcut logging (3.2M ha) represented 57% of all anthropogenic disturbances, reducing potential primary forest by 2.7 million ha (28%) for the IWB and 524,003 ha (39%) for the ITR. Decadal logging rates nearly doubled from 5.3% to 10.2% from 1970s–2000s. Core areas (buffered by 100-m from roads and developments) declined by 70% to 95% for the IWB and ITR, respectively. Vulnerable was assigned to karst, the only abiotic factor assessed, because it was associated with rare plants. For biotic factors, Old-Growth Birds were Vulnerable, Southern Woodland Caribou (Rangifer tarandus caribou) habitat and Sensitive Fish were Endangered, and Old-Growth Lichens habitat was Critical. Overall, the IWB was ranked as Endangered and the ITR as Critical with core area collapse possible within 9 to 18 years for the ITR, considered one of the world’s most imperiled temperate rainforests.

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