Two-sex matrix models in assessing population viability: When do male dynamics matter?

While most demographic population models used in conservation rely on female vital rates, recent empirical evidence suggests that male dynamics should be included in population models used for assessing extinction risk. Using California sea lions Zalophus californianus as an applied example, we demonstrate that there are situations in which two-sex models are more appropriate than the commonly used female-based model. Two-sex models are relevant in cases where vital rates for sexes differ and for polygamous species such as sea lions. Vital rates targeted for management may therefore respond differently for males and females and for different assumptions about sex ratio. Synthesis and applications. Conservation biologists should carefully consider the social structure and sex ratio of focal species in order to determine whether a two-sex matrix model will yield more accurate estimates of extinction risk than standard one-sex models.