Eigenvalue elasticity analysis of species life histories for conservation and management: Methods and applications.

摘要

Accurate assessment of extinction probability requires long-term studies to identify means, variances and co-variances of vital rates (age- or stage-specific survival, growth, and fertility). This type of information is rare, and for most threatened species there is not enough time or resources to obtain it. For declining populations that are fairly large, simpler models may help guide research and initial management plans. Elasticity analysis of deterministic matrix models predicts the proportional change in the population growth rate ({dollar}lambda{dollar}) following a proportional change in one or more vital rates in the absence of density-dependence. Species which share life history traits and elasticity patterns may respond similarly to perturbations that affect particular life stages. My work is a synthesis of published demographic data for vertebrates and matrix modeling techniques. My goals were: (1) to examine similarities in life history traits to determine what factors most affect elasticity patterns, specifically the proportional contributions of reproduction, juvenile survival and adult survival to population growth, (2) to develop a method for predicting elasticity patterns without complete age-specific survival information, and (3) to apply these methods to specific management problems and suggest how elasticity analysis can aid species conservation.; I found that age at maturity, adult survival and {dollar}lambda{dollar} determine the elasticity patterns of age-based model populations. The growth rates of populations with short generation times are highly dependent on fertility and survival rates of newborns while species with long generation times and late age at maturity showed very low fertility/age 0 elasticities. The ratio of adult:age 0 elasticity indicates the proportional increase in egg production or survival that would be required to compensate for adult harvest. Some fishes can increase fertility dramatically, while species with only a few offspring per year (e.g., sharks, whales) cannot. This may be one of the reasons why long-lived, less fecund species are easily overexploited.; Elasticity analysis may be valuable to managers who are trying to assess the relative impacts of disturbance or mitigation on declining populations. It is also a tool for comparing the life histories of different species and provides a framework for choosing model populations for viability analysis.