Dynamics of the new south wales yellow-footed rock­wallaby population, in relation to rainfall patterns

Abstract

Yellow-footed rock-wallabies (Petrogale xanthopus) are listed as endangered in New South Wales (NSW). Annual helicopter surveys have been conducted, during winter, on the NSW population since 1980. Correlation analysis suggested that the exponential rate of increase (r) of the population was positively related to rainfall in the previous calender year. Ivlev's inverted exponential numerical response model was found to adequately represent the relationship between r and rainfall, though the fit was poor (R² = 0.43). Examination of the fit of the numerical response model and the predictions for the consonants used in the model suggested that the lower end of the function was better approximated than the upper end. The predicted values for the maximum rate of decrease and the level of rainfall at which r would became positive could be intuitively explained given aspects of the wallabies' ecology. However, the estimated maximum rate of increase was far below theoretically predicted values, which suggested that the expected positive correlation between rainfall and recruitment was weak. This suggested that the NSW P. xanthopus population was not primarily regulated by absolute resource availability during the period of the study. Possible intrinsic and extrinsic factors that detrimentally influenced the population are proposed.