Theoretical modelling predicts that both direct and delayed
density-dependence are key factors to generate population cycles.
Deciphering density-dependent processes that lead to variable population
growth characterizing different phases of the cycles remain challenging.
This is particularly the case for the period of prolonged low densities,
which is inherently data deficient. However, demographic analyses based
on long-term capture-mark-recapture datasets can help resolve this
question. We relied on a 16-yr (2004-2019) live-trapping program to
analyse the summer demography and movements of a cyclic brown lemming
population in the Canadian Arctic. More specifically, we examined if
inversely density-dependent processes could explain why population
growth can remain low during the prolonged low phase. We found that the
proportion of females in the population was inversely density-dependent
with a strong male-biased sex ratio at low densities but not at high
densities. However, survival of adult females was higher than adult
males, but both had lower survival at low densities than at high ones.
Distances moved by both adult males and females were density-dependent,
and proportion of females in reproductive condition was weakly
density-dependent as it tended to increase at low density. Individual
body condition, measured as monthly change in body mass, was not
density-dependent. Overall, the strong male-biased sex ratio at very low
densities suggests a loss of reproductive potential due to the rarity of
females and appears to be the most susceptible demographic factor that
could contribute to the prolonged low phase in cyclic brown lemmings.
What leads to this sex-bias in the first place is still unclear,
potentially owing to our trapping period limited to the summer, but we
suggest that it could be due to high predations rate on breeding females