15 views
why sex ratio is important
Sex ratio affects both the growth rates and the evolutionary trajectories of wild populations. The sex ratio of the population affects, and is affected by, birth, death, immigration, and emigration rates. It is measured as the ratio of the number of individuals of one sex to that of the other sex, or the ratio of allocation in each. The production of males and females in a ratio of 1:1 is generally the most common evolutionary stable strategy (ESS), led by frequency-dependent natural selection due to competition for mates among individuals of the same sex. Natural selection often appears to determine the differences within and among populations and species in sex ratio. The optimum sex ratio for a given individual in a given population depends on both the existing sex ratio of the population and on the relative costs and benefits of producing offspring of each gender. Patterns of natural selection on sex ratio may be affected by the quality and stability of the immediate habitat, as well as by life-history traits, competition and dispersal, which affect local competition on mate or resources. Environmental effects, both temporal and spatial, can create a biased sex ratio by excess production of the sex that is cheaper to produce under poor environmental conditions. Moreover, empirical studies have found that the sex ratio in plants can be modified at the individual level, following seasonal changes in the resources available.
Sex ratios are among the most basic of demographic parameters and provide an indication of both the relative survival of females and males and the future breeding potential of a population. The observed sex ratio is a consequence of natural selection on the sexes and any anthropogenic effects of harvest. This allows wildlife managers to regulate animal harvests to try to maintain desired sex ratios. Conversely, by monitoring sex ratios, wildlife managers can assess how harvest regulations may be influencing the relative mortality rates of the male and female segments of a population.
In this chapter, two general approaches to estimating sex ratios were addressed . The most general approach used direct field observations to estimate the population sex ratio. Finite sampling methods were used to estimate these ratios under a variety of scenarios. Choosing among these methods should begin with the structure and nature of the population under investigation. Species that form aggregates or herds need to be surveyed differently than populations of solitary individuals. Cluster sampling techniques were therefore presented. Unequal probabilities of detection are possible when making visual counts of animals. This consideration is important when probabilities of detecting animal aggregations of different sizes are expected to be a function of group size. The advantage of direct estimation methods for calculating sex ratios is that no assumption is required about the dynamics of the population being studied. Instead adherence to the principles of probabilistic sampling is all that is needed to ensure reliable estimation of population sex ratios. Although easily said the validity of the demographic study relies totally on the design and conduct of the sample survey.
Sex ratios are among the most basic of demographic parameters and provide an indication of both the relative survival of females and males and the future breeding potential of a population. The observed sex ratio is a consequence of natural selection on the sexes and any anthropogenic effects of harvest. This allows wildlife managers to regulate animal harvests to try to maintain desired sex ratios. Conversely, by monitoring sex ratios, wildlife managers can assess how harvest regulations may be influencing the relative mortality rates of the male and female segments of a population.
In this chapter, two general approaches to estimating sex ratios were addressed . The most general approach used direct field observations to estimate the population sex ratio. Finite sampling methods were used to estimate these ratios under a variety of scenarios. Choosing among these methods should begin with the structure and nature of the population under investigation. Species that form aggregates or herds need to be surveyed differently than populations of solitary individuals. Cluster sampling techniques were therefore presented. Unequal probabilities of detection are possible when making visual counts of animals. This consideration is important when probabilities of detecting animal aggregations of different sizes are expected to be a function of group size. The advantage of direct estimation methods for calculating sex ratios is that no assumption is required about the dynamics of the population being studied. Instead adherence to the principles of probabilistic sampling is all that is needed to ensure reliable estimation of population sex ratios. Although easily said the validity of the demographic study relies totally on the design and conduct of the sample survey.
