Sympatric predator odour reveals a competitive relationship in size-structured mammalian carnivores

Interspecific competition between sympatric carnivores can have a profound effect on the structure, function and composition of ecosystems. Interspecific competition is often asymmetrical and the smaller carnivore is usually affected the most. We investigated the behavioural responses of two native species, the larger Tasmanian devil (Sarcophilus harrisii) and the smaller spotted-tailed quoll (Dasyurus maculatus) to each other's odour and to that of an introduced predator, the feral cat (Felis catus), in north-west Tasmania, Australia. We used an experimental array of camera traps, in which carnivore scats were added as treatments. Behavioural responses exhibited by devils and quolls are indicative of a dominant predator-mesopredator relationship and suggest the potential for interspecific competition. The larger predator, the devil, was as vigilant at quoll odour as at control camera traps, but showed decreased vigilance at cat odour and did not avoid cat or quoll odours. The smaller predator, the spotted-tailed quoll, increased its vigilance near devil odour compared to control camera traps but did not avoid it. This experiment shows that assessing the behavioural responses of sympatric carnivores to each other's odour can help understand predator interactions and reveal the potential for interspecific competition. Understanding these interactions is crucial in managing and conserving carnivores. Animals navigate through an environment full of faecal odours left by predators, competitors and conspecifics. These odours provide information on both the immediate presence and the indirect risk of encountering a predator or an aggressive competitor. Tasmania's largest predator, the Tasmanian devil, coexists with the smaller spotted-tailed quoll and the introduced feral cat. We tested the behavioural responses of Tasmanian devils and spotted-tailed quolls to each other's faecal odour and to cat faecal odour. Behavioural patterns exhibited by predators in this experiment are indicative of a dominant predator-mesopredator relationship and suggest the potential for interspecific competition. Knowledge of the ecological interactions amongst sympatric carnivores can aid managers in making more informed decisions when trying to achieve specific conservation goals.