ANALYSES OF SEXUAL SIZE DIMORPHISM USING NULL GROWTH-BASED MODELS

When animals mature at small sizes and then grow to larger asymptotic sizes, many different factors can affect adult male and female size di stributions. This paper shows how growth-based models can be used to s tudy the factors affecting sexual size dimorphism in species with asym ptotic growth after maturity. Null growth-based models assume that the males and females in a particular sample exhibit the growth and matur ation patterns previously described for the members of their taxon and that the males and females in that sample have identical age distribu tions. Discrepancies between the size distributions predicted by the n ull model and those observed in a sample indicate significant sex diff erences in adult age distributions or, in the growth trajectories of p articular age classes. The design and use of null growth-based models is illustrated using lizards of the genus Anolis. The results of these analyses show that samples of anoles often have male size distributio ns skewed in favor of larger-than-expected males and provide support f or behavioral hypotheses that predict skewed adult male size distribut ions when males compete for breeding territories.