Density-dependent demography and movements in a cyclic brown lemming population

Area of Science:

• Ecology
• Population Dynamics
• Arctic Biology

Background:

• Population cycles are influenced by density-dependence, but factors causing prolonged low phases are poorly understood.
• Demographic analyses of long-term data are crucial for deciphering these complex population dynamics.

Purpose of the Study:

• To investigate inversely density-dependent processes potentially explaining prolonged low densities in cyclic brown lemming populations.
• To analyze summer demography and movement patterns using a 16-year capture-mark-recapture dataset.

Main Methods:

• Live-trapping of brown lemmings over 16 years (2004-2019) in the Canadian Arctic.
• Analysis of sex ratio, survival rates, movement distances, reproductive condition, and body condition in relation to population density.

Main Results:

• A male-biased sex ratio was observed at low densities, becoming less pronounced at high densities.
• Adult female survival was higher than males but decreased at low densities.
• Movement distances were density-dependent; reproductive condition weakly increased at low densities.
• Individual body condition showed no density-dependence.

Conclusions:

• The strong male-biased sex ratio at low densities significantly reduces reproductive potential, likely contributing to prolonged low phases in cyclic brown lemmings.
• While the cause of the sex bias is unclear, high winter predation on breeding females is a potential factor.
• Further research is needed to elucidate the origins of this density-dependent sex ratio bias.