Odour-mediated Interactions Between an Apex Reptilian Predator and its Mammalian Prey

Christopher R Dickman,Nicole Hills,Loren L Fardell

doi:10.1007/s10886-022-01350-w

Abstract

An important but understudied modality for eavesdropping between predators and prey is olfaction, especially between non-mammalian vertebrate predators and their prey. Here we test three olfactory eavesdropping predictions involving an apex reptilian predator, the sand goanna Varanus gouldii, and several species of its small mammalian prey in arid central Australia: 1) small mammals will recognize and avoid the odour of V. gouldii; 2) V. gouldii will be attracted to the odour of small mammals, especially of species that maximize its energetic returns; and 3) small mammals will be less mobile and will show higher burrow fidelity where V. gouldii is absent compared with where it is present. As expected, we found that small mammals recognized and avoided faecal odour of this goanna, feeding less intensively at food patches where the odour of V. gouldii was present than at patches with no odour or a pungency control odour. Varanus gouldii also was attracted to the odour of small mammals in artificial burrows and dug more frequently at burrows containing the odour of species that were energetically profitable than at those of species likely to yield diminishing returns. Our third prediction received mixed support. Rates of movement of three species of small mammals were no different where V. gouldii was present or absent, but burrow fidelity in two of these species increased as expected where V. gouldii had been removed. We conclude that olfaction plays a key role in the dynamic interaction between V. gouldii and its mammalian prey, with the interactants using olfaction to balance their respective costs of foraging and reducing predation risk. We speculate that the risk of predation from this apex reptilian predator drives the highly unusual burrow-shifting behaviour that characterizes many of Australia's small desert mammals.

Highlights

In situations where prey are naïve to predators and do not recognize their olfactory cues, such as where prey or predator species have been introduced to a new environment, prey mortality may be high and local populations will be at high risk of extinction (Salo et al 2007)
We presented the odour of three species of small mammals—one odour per artificial burrow—and placed fresh cotton wool in the fourth burrow to serve as an odourless control
More visits were made by the study species to giving-up density (GUD) sites with no odour over the seven nights of the experiment than to sites with the pungency control, with fewest visits made to sites with the odour of V. gouldii

Summary

Introduction

All organisms release chemical compounds into the environment. Some of these compounds are shed as excreta or produced during the decomposition process after death, whereas others are metabolic products that can convey specific information to conspecific or heterospecific individuals (Vos et al 2006). Journal of Chemical Ecology (2022) 48:401–415 prey may respond to a predatory odour cue by investigating, freezing, or fleeing from the site of the cue, and show acute or chronic stress (Fardell et al 2020) as well as latent effects on their levels of vigilance behaviour, habitat use, temporal and spatial activity (Fenn and Macdonald 1995; Parsons and Blumstein 2010a, b; Cox et al 2012; Parsons et al 2018) These responses are often calibrated according to the specific identity of the predator and the level of threat that it poses to prey (Dickman 1992; Anson and Dickman 2013; Grau et al 2019), and to factors such as the source of the odour (e.g. urine or faeces), its age and intensity (Fendt et al 2020), and the prior experience of prey individuals with predators (Bleicher et al 2018). In situations where prey are naïve to predators and do not recognize their olfactory cues, such as where prey or predator species have been introduced to a new environment, prey mortality may be high and local populations will be at high risk of extinction (Salo et al 2007)

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Results

Conclusion