The northern arid zone of Australia is notable because of the unpredictable rainfall patterns that it experiences. Rainfall, when it does occur in sufficient quantity, results in pulses in primary productivity that can lead to population outbreaks of native rodents (Muridae). Not all species of rodent respond to each resource pulse. Perhaps the best example of this irregularity is the long-haired rat (Rattus villosissimus), the largest extant rodent in arid Australia (body mass: 150 g). The species is not resident in our study area in the western Simpson Desert, rather population outbreaks occur every 25-30 years. Such outbreaks have significant impacts on the biotic and abiotic environment. Here, we report on an outbreak that occurred from June 2010 to December 2012 and the subsequent response to the disappearance of the rats. The ecological impacts of disruptive events such as the outbreak of the long-haired rat are poorly understood in arid ecosystems; therefore we focussed our attention on this event.
Results/Conclusions
The long-haired rat outbreak in 2010-2012 resulted in a series of novel ecological interactions; these interactions had not been observed during the periods when the rat was not present. The novel interactions that we observed were; 1) long-haired rat predation on smaller mammals (body mass <100 g) especially other rodents; 2) invasion by the rats in to refuge habitat of the nationally vulnerable plains mouse (Pseudomys australis), and 3) feeding and associated damage to the nationally vulnerable keystone tree species (Acacia peuce). In addition, long-haired rat burrow construction resulted in large volumes of soil redistribution. Further, the presence of rats produced a spike in rodent biomass that was over twice that during irruptions where the rat was absent. The sporadic occurrence of the long-haired rat and the intensity and spatial scale of the novel interactions lead us to consider it a disruptive factor in the functioning of the Simpson Desert ecosystem.