Identifying a limiting factor in the population dynamics of a threatened amphibian: The influence of extended female maturation on operational sex ratio

Abstract

AbstractUnderstanding amphibian population dynamics is integral to mitigating severe declines that are occurring due to threats such as habitat removal and chytrid‐induced disease. Few studies have focused on sex‐specific population dynamics, despite the potential for these processes to alter colonisation and population turn‐over in newly created habitats. Here, we investigate sex‐specific population dynamics in the threatened green and golden bell frog (Litoria aurea) using intensive capture‐recapture methods in a newly created wetland complex and control sites. As hypothesised, females took longer to reach maturity compared to males. The length of female maturation was 3.9 times greater than that of males (428.68 days ± 107.6 SD and 110.16 days ± 20.59 SD, respectively). This resulted in a one‐year delay in female population size increase compared to the male population. The operational sex ratio (OSR) in the second year of monitoring in the created wetlands had the most disproportionate male bias out of any year and any site (12/1 male/female, male proportion = 0.92 ± 0.89–0.94 95% CI). In the third year, the OSR had become less male biased (2.6/1, male proportion = 0.72 ± 65–0.78 95% CI), likely attributed to the maturing of the females produced in the first year breeding events. We did not find any evidence that survival or detection probability influenced the observed OSRs in the created wetlands. Based on survival rates of each sex, we estimate that males are 77 times more likely to reach sexual maturity compared to females. We postulate that the combination of chytrid‐induced disease and sex‐biased maturation rates may be a driver of declines, especially in populations with limited recruitment. We encourage future research into investigating sex‐specific population dynamics of amphibians, especially relating to reintroduction ecology and disease.