Determinants of lemming outbreaks

Abstract

Population outbreaks in tundra rodents have intrigued scientists for a century as a result of their spectacular appearances and their general lessons in ecology. One outstanding question that has led to competing hypotheses is why sympatric lemmings and voles differ in regularity and shape of their outbreaks. Lemming outbreaks may be lost for decades while vole populations maintain regular population cycles. Moreover, when lemming populations eventually irrupt, they do so more steeply than the vole populations. Norwegian lemmings exhibited a large-scale outbreak synchronously with gray-sided voles in Finnmark, northern Fennoscandia, during 2006 to 2007 for the first time in two decades. Analyses of spatial variability of this outbreak across altitudinal gradients allowed us to identify determinants of the contrasting lemming and vole dynamics. The steeper lemming outbreak trajectories were caused by breeding and population growth during winter, when nonbreeding vole populations consistently declined. The differently shaped lemming and vole outbreaks appear to result from a particular demographic tactic of lemmings that evolved as an adaptation to the long and cold Arctic-Alpine winters. The lemming outbreak amplitude increased with altitude and vole density, indicating that lemming outbreaks are jointly facilitated by low temperatures and apparent mutualism with voles mediated by shared predators. High sensitivity to variation in climate and predation is likely to be the reasons why lemmings have more erratic population dynamics than sympatric voles. The combination of continued climatic warming and dampened vole cycles is expected to further decrease the frequency, amplitude, and geographic range of lemming outbreaks in tundra ecosystems.arctic tundra | climate impact | density dependence | spatial population dynamics F or centuries, lemmings have caught the attention of naturalists and scientists as a result of their spectacular population dynamics and keystone functioning in tundra ecosystems (1-4). Charles Elton (5) was the first to recognize the cyclic nature of lemming population outbreaks-a discovery that initiated a lasting research tradition that aims to identify causes of multiannual cycles in animal populations (6).Current research on lemmings has been fueled by two recent discoveries made in the case of the Norwegian lemming Lemmus lemmus, the most renowned lemming species (3). The first is that its outbreak trajectory is differently shaped from that of the graysided vole (Myodes rufocanus), the often codominant rodent species, which always exhibits population peaks synchronously with the lemming. Specifically, the lemming population erupts more steeply than the vole population. This discrepancy in "outbreak topology" has been suggested to result from different trophic interactions; the "sharp" lemming outbreaks from an interaction with food plants, the "blunt" vole peaks from an interaction with predators (7, 8). However, there are still contrasting views on which factors regulate lemming population...

Ecosystem drivers of an Arctic fox population at the western fringe of the Eurasian Arctic

“…It is also important to note that the Norwegian lemming has been almost absent in the catches since the 2011 peak and therefore appears to have missed the last peak in 2015. That lemmings are missing during certain rodent peaks appears to be a common phenomenon in northern Fennoscandia (Angerbjörn et al 2001;Ekerholm et al 2001;Ims et al 2011). In fact, a paucity of lemming peaks in Finnmark was observed between 1988 and 2007, although the greysided vole had a regular four-to five-year cycle in the same period (Oksanen et al 2008;Ims et al 2011).…”

“…That lemmings are missing during certain rodent peaks appears to be a common phenomenon in northern Fennoscandia (Angerbjörn et al 2001;Ekerholm et al 2001;Ims et al 2011). In fact, a paucity of lemming peaks in Finnmark was observed between 1988 and 2007, although the greysided vole had a regular four-to five-year cycle in the same period (Oksanen et al 2008;Ims et al 2011). The irregularity of the lemming outbreak dynamics compared to the more regular vole cycle has been attributed to higher sensitivity of lemmings to winter climate Ims et al 2011).…”

Effects of changing permafrost and snow conditions on tundra wildlife: critical places and times

“…In contrast, lemmings will be affected negatively through a longer period with more intense predation. Even biologically similar herbivores like lemmings and voles are suspected to have different sensitivities to altered physical snow properties (Ims et al 2011). …”

Range Extensions of Some Boreal Owl Species: Comments on Snow Cover, Ice Crusts, and Climate Change

“…A study of comparative population development between L. lemmus and M. rufocanus in Finnmark, northern Norway, revealed significant ecological differences between the two species (Ims et al, 2011). The Arctic lemming has evolved a population "kick-starter."…”

“…The lemming outbreak amplitude increased with altitude and vole density, indicating that lemming outbreaks are jointly facilitated by low temperatures and apparent mutualism with voles mediated by shared predators. The combination of continued climatic warming and dampened vole cycles is expected to further decrease the frequency, amplitude, and geographical range of lemming outbreaks in tundra ecosystems (Ims et al, 2011). A more modest summer effect indicates that some additional mechanism also contributes, for instance, temperature-dependent quality of mosses (Tast, 1991;Ims et al, 2011). wInter "KIcK-start" In wood lemmInG?…”