Abstract The Euler–Lotka equation is widely used in life table analysis to estimate population growth rates from age‐specific demographic parameters. These parameters are typically estimated from cohort experiments using either the female‐only method, which relies exclusively on data from females, or the two‐sex method, which uses data from all individuals. The rationale for applying the two‐sex method is to incorporate male effects on population growth that are absent from the female‐only method. This study shows that this rationale is not supported because, when female demography is fixed as in the Euler–Lotka equation, population growth of sexual species is independent of male demography. A recent study suggested that the female‐only and two‐sex methods are equivalent and interchangeable. The present study demonstrates that they are not equivalent in practice and identifies specific methodological issues associated with the two‐sex method through case studies and analyses of empirical data. The restrictive two‐sex method may be regarded as an approximation to a specific case of the more general female‐only method. Even if that specific case is unrealistic, the two‐sex method provides no flexibility to relax its underlying assumptions.
Toshinori Okuyama (Sat,) studied this question.