Population Dynamics of The Allied Rock-wallaby Petrogale assimilis: Implications for Conservation.

Abstract

Most species of Petrogale live in the arid inland or in the wet-dry tropics of northern Australia. These environments are characterised by the unpredictability of their rainfall, and the reproductive strategies of the animals reflect this. I studied one population of Petrogale assimilis during a period of extended drought. During this time mortality of young (ca. 88%) and adults (≥ 25%) was very high and recruitment into the adult population was negligible. The age structure of the population was skewed towards very old animals and pouch young. Evidence from this and other populations suggests that recruitment into the breeding population is spasmodic, reflecting the irregular pattern of good seasons. Recruitment events may occur asynchronously in neighbouring populations depending on the spatial and temporal variability of the rain. If true, rock-wallaby populations irregularly pass through periods of low numbers and demographic instability. Careful monitoring and management decisions are therefore important. At low points in this climatic cycle additional factors (e.g., predators) could have a devastating impact. We need to protect a relatively large area of habitat to compensate for the asynchronous pulsing of populations and to allow populations to recover. Survey design must also allow for this demographic instability.