Inferences about ungulate population dynamics derived from age ratios

Nyeema C. Harris, Matthew J. Kauffman, L. Scott Mills

Research output: Contribution to journalArticlepeer-review

50 Scopus citations

Abstract

Age ratios (e.g., calf:cow for elk and fawn:doe for deer) are used regularly to monitor ungulate populations. However, it remains unclear what inferences are appropriate from this index because multiple vital rate changes can influence the observed ratio. We used modeling based on elk (Cervus elaphus) life-history to evaluate both how age ratios are influenced by stage-specific fecundity and survival and how well age ratios track population dynamics. Although all vital rates have the potential to influence calf:adult female ratios (i.e., calf:xow ratios), calf survival explained the vast majority of variation in calf:adult female ratios due to its temporal variation compared to other vital rates. Calf:adult female ratios were positively correlated with population growth rate (λ) and often successfully indicated population trajectories. However, calf:adult female ratios performed poorly at detecting imposed declines in calf survival, suggesting that only the most severe declines would be rapidly detected. Our analyses clarify that managers can use accurate, unbiased age ratios to monitor arguably the most important components contributing to sustainable ungulate populations, survival rate of young and λ. However, age ratios are not useful for detecting gradual declines in survival of young or making inferences about fecundity or adult survival in ungulate populations. Therefore, age ratios coupled with independent estimates of population growth or population size are necessary to monitor ungulate population demography and dynamics closely through time.

Original languageEnglish
Pages (from-to)1143-1151
Number of pages9
JournalJournal of Wildlife Management
Volume72
Issue number5
DOIs
StatePublished - Jul 2008

Keywords

  • Age ratios
  • Cervus elaphus
  • Elk
  • Indices
  • Life-stage simulation analysis
  • Monitoring
  • Population growth rate
  • Recruitment
  • Sensitivity analysis
  • Survival
  • Ungulate

Fingerprint

Dive into the research topics of 'Inferences about ungulate population dynamics derived from age ratios'. Together they form a unique fingerprint.

Cite this