Variety is the spice of life histories: comparison of intraspecific variability in marine invertebrates.

Life-history characteristics of marine invertebrates exhibit broad diversity across taxa as well as considerable variation within species. Although such variation is widely recognized, comparisons of the magnitude of variability as an outcome of evolutionary processes are relatively rare. Theory predicts, for example, that patterns of variability within and between clutches can arise as a consequence of population genetic structure, environmental variability, and the uncertainty of future ecological conditions. We review the strengths and weaknesses of several statistical methods for comparing variability across distributions, including Levene's test, use of the coefficient of variation in F-tests, and analysis of covariance. We then use four case studies from our own work and from the literature to illustrate adaptive patterns of variability related to metamorphosis, habitat differentiation, physiological stress, and life-history mode. These examples demonstrate the value of comparing variability for a range of questions associated with reproductive ecology, life-history biology, and genotype-by-environment interactions. We encourage researchers studying larval ecology and life-history evolution to explicitly consider the causes and consequences of variances in traits along with their means in models, experimental designs, analyses, and interpretations.