Population demography of frillneck lizards (Chlamydosaurus kingii, Gray 1825) in the wet-dry tropics of Australia

We explore the effects of biotic and abiotic factors on the population demography of frillneck lizards (Chlamydosaurus kingii) in the Australian wet-dry tropics. Annual growth rates of males were significantly higher across all body sizes compared to females, resulting in a significant larger maximum body size in males. Both male and female lizards were highly philopatric and 81% of the among-year recapture distances were less than 200 m. Juvenile and adult frillnecks were subjected to low but highly variable annual survival rates. Both proportion of juveniles and relative proportion of reproductive females showed extensive among-year variations. No relationship was, however, observed between proportion of gravid females and that of juveniles captured during the subsequent year. High rainfall in January was negatively correlated with recruitment most likely caused by increased egg/embryo mortality due to flooding of nest sites. We therefore suggest that the lack of association between female reproduction and juvenile recruitment was due to the effects of stochastic variation in January rainfall. Lizard numbers increased during the first five years of the study followed by a decline during the subsequent four years. Our analyses show that annual variation in survival constituted the main determinant in driving the annual change in frillneck numbers. Surprisingly, no relationship was observed between fillneck population dynamics and annual variation in juvenile recruitment. We suggest that the 7-years over which these analyses were conducted were insufficient to detect any significant effects of recruitment on lizard numbers, demonstrating the need for long-term studies to accurately document vertebrate population demographic processes in areas experiencing stochastic variations rainfall such as the Australian wet-dry tropics.