Seasonal demography of a cyclic lemming population in theCanadianArctic

Abstract

Summary1. The causes of cyclical fluctuations in animal populations remain a controversial topic in ecology. Food limitation and predation are two leading hypotheses to explain small mammal population dynamics in northern environments. We documented the seasonal timing of the decline phases and demographic parameters (survival and reproduction) associated with population changes in lemmings, allowing us to evaluate some predictions from these two hypotheses. 2. We studied the demography of brown lemmings (Lemmus trimucronatus), a species showing 3-to 4-year population cycles in the Canadian Arctic, by combining capture-mark-recapture analysis of summer live-trapping with monitoring of winter nests over a 10-year period. We also examined the effects of some weather variables on survival. 3. We found that population declines after a peak occurred between the summer and winter period and not during the winter. During the summer, population growth was driven by change in survival, but not in fecundity or proportion of juveniles, whereas in winter population growth was driven by changes in late summer and winter reproduction. 4. We did not find evidence for direct density dependence on summer demographic parameters, though our analysis was constrained by the paucity of data during the low phase. Body mass, however, was highest in peak years. 5. Weather effects were detected only in early summer when lemming survival was positively related to snow depth at the onset of melt but negatively related to rainfall. 6. Our results show that high mortality causes population declines of lemmings during summer and fall, which suggests that predation is sufficient to cause population crashes, whereas high winter fecundity is the primary factor leading to population irruptions. The positive association between snow depth and early summer survival may be due to the protective cover offered by snow against predators. It is still unclear why reproduction remains low during the low phase.

Top‐down limitation of lemmings revealed by experimental reduction of predators

“…Each captured lemming was identified to species, sexed, weighed, and tagged with a passive integrated transponder (PIT) or a uniquely numbered ear‐tag (see Fauteux et al. for details). For the purpose of the current study, we focused on the 2008–2015 period, when live trapping data were collected on both trapping grids.…”

“…For instance, population growth may be mainly limited by mortality during periods of high predation rate while it may be limited by reproduction (i.e., resource availability) during periods of low predation rate such as when individuals are protected from predators by the snow (Fauteux et al. ). Predation and food availability may thus both play a role as the strength of trophic interactions can vary through time at a single site (Sinclair et al.…”

“…, Fauteux et al. ). Manipulating predation in the field, however, is a daunting task and previous studies have reported multiple potential problems such as mechanical failures of fences (e.g., predators going through fences, Reid et al.…”

Population cycles: generalities, exceptions and remaining mysteries

“…populations is that cycles are caused not only by changes in mortality but also by changes in reproduction [41].…”

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

“…Moreover, since density and shear strength are positively correlated (Domine et al 2011), dense snow may also increase the energetic costs of tunneling to access food. Winter reproduction is an important prerequisite for high-amplitude cyclic peaks in lemmings (Ims et al 2008;Fauteux et al 2015).…”