Naivety, therefore, is fundamentally a case of evolutionary mismatch between a novel predator’s cues and the cue detection and response process of prey 3.Īustralia has the worst extinction record globally for small and medium-sized native mammals 6, a fact that has been attributed to prey naivety towards introduced dogs ( Canis lupus familiaris), foxes ( Vulpes vulpes), and cats ( Felis catus), all introduced by humans some 150 years ago 10, 25. Thus, alien predators that are sufficiently novel may circumvent the detection processes of native prey, leading to naivety and its attendant consequences 11, 18, 19, 24. The prey’s perceptual and cognitive processes, as well as their response bias, are shaped by the prey’s evolutionary experience with native predators and their cues 6, 24. The second component is the animal’s response bias, which reflects the relative costs of under-responding versus over-responding to the cue.
The first is cue discriminability, or how well the animal can identify the cue, which necessarily involves the sensory and perceptual systems. Detection theory 24 posits that there are two components underpinning a response. For an animal to respond to a cue, both perceptual and cognitive processes are required. In the broadest sense, a cue is sensory information available to the prey that indicates the presence, or the potential presence, of the predator. 12, 13, 14, 15), the critical question of whether distantly related mammalian carnivores produce different odours remains unanswered. While many studies have demonstrated a lack of response to alien predator odours in native prey (e.g.
Olfactory predator recognition is a powerful system in which to test this idea, because most mammals and many vertebrates have a highly developed olfactory system and use the information contained in odour cues to recognise and avoid their predators 22, among many other varied and important functions 23. Yet to date, this key prediction remains untested. But why do native prey fail to recognise alien predators? Naivety theory is predicated on the idea that novel predators emit novel cues 18, 19, 20, 21. Native prey naivety has been observed in many invaded environments 11. There is a large body of research into native prey naivety towards alien predators, which is usually experimentally assessed as a failure to recognise alien predators’ olfactory (e.g. Alien predators have twice the impact that native predators have on native prey 9, a phenomenon thought to be driven by prey naivety, or the failure to recognise an alien predator and respond accordingly 10, 11. Understanding biotic interactions between alien and native species can help to predict not only invader impacts, but also the establishment and spread of invasive species 7, 8. The introduction of species beyond their native ranges leads to the disruption of coevolved detection and communication systems 3, 4, leading in many cases to devastating impacts 5, 6. The ability to detect and recognise predators is crucial for survival, and is learned or evolved over long periods of shared evolutionary history 1, 2. Our results also suggest a role for olfactory cues to complement visual appearance and vocalisations as biologically meaningful ways to differentiate species.
Chemical profiles showed little overlap between placental and marsupial carnivores across all odour types, suggesting that cue novelty is a plausible mechanism for prey naivety towards alien predators. We compared volatile chemical profiles of urine, scats and bedding from four placental and three marsupial predators. We investigate whether odour cues differ between placental and marsupial carnivores in Australia, where native prey experienced only marsupial mammal predation until ~4000 years ago. Yet it also possible that all predators emit similar cues because they are carnivorous. Distantly related animals have distinct evolutionary histories, physiologies and ecologies, predicting they will emit different cues. Naivety theory predicts that it is because novel predators emit novel cues. Yet exactly why native prey fail to recognise alien predators remains puzzling. The classic example is prey naivety towards alien predators, whereby prey fail to recognise a new predator. Introduced species disrupt coevolved systems of communication and detection in their new ranges, often leading to devastating impacts. Detecting enemies is crucial for survival and a trait that develops over an evolutionary timeframe.
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