title: Demographic origins of skewed operational and adult sex ratios: perturbation analyses of two-sex models.
abstract: Skewed sex ratios - operational (OSR) and Adult (ASR) - arise from sexual differences in reproductive behaviours and adult survival rates due to the cost of reproduction. However, skewed sex-ratio at birth, sex-biased dispersal and immigration, and sexual differences in juvenile mortality may also contribute. We present a framework to decompose the roles of demographic traits on sex ratios using perturbation analyses of two-sex matrix population models. Metrics of sensitivity are derived from analyses of sensitivity, elasticity, life-table response experiments and life stage simulation analyses, and applied to the stable stage distribution instead of lambda. We use these approaches to examine causes of male-biased sex ratios in two populations of green-rumped parrotlets (Forpus passerinus) in Venezuela. Female local juvenile survival contributed the most to the unbalanced OSR and ASR due to a female-biased dispersal rate, suggesting sexual differences in philopatry can influence sex ratios more strongly than the cost of reproduction.
authors.affiliation: Ecosystem Sciences Division, Department of Environmental Science, Policy & Management, University of California, Berkeley, CA 94720-3114, USA.
authors.forename: Sophie
authors.initials: S
authors.lastname: Veran
authors.forename: Steven R
authors.initials: SR
authors.lastname: Beissinger
mesh_terms: D025041:Animal Migration; D000818:Animals; D005260:Female; D008297:Male; D008962:Models, Theoretical; D011157:Population Dynamics; D011563:Psittaciformes / Q000502:physiology*; D012727:Sex Characteristics; D012744:Sex Ratio; D012726:Sexual Behavior, Animal; D014687:Venezuela