Trophic cascade driven by behavioural fine-tuning as naive prey rapidly adjust to a novel predator

Jolly, C. J.; Smart, A. S.; Moreen, J.; Webb, J. K.; Gillespie, G. R.; Phillips, B. L.

doi:10.1101/856997

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bioRxiv · 10.1101/856997

Trophic cascade driven by behavioural fine-tuning as naive prey rapidly adjust to a novel predator

Jolly, C. J.·Smart, A. S.·Moreen, J.·Webb, J. K.·Gillespie, G. R.·Phillips, B. L.

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Abstract

AO_SCPLOWBSTRACTC_SCPLOWThe arrival of novel predators can trigger trophic cascades driven by shifts in prey numbers. Predators also elicit behavioural change in prey populations, via phenotypic plasticity and/or rapid evolution, and such changes may also contribute to trophic cascades. Here we document rapid demographic and behavioural changes in populations of a prey species (grassland melomys Melomys burtoni, a granivorous rodent) following the introduction of a novel marsupial predator (northern quoll Dasyurus hallucatus). Within months of quolls appearing, populations of melomys exhibited reduced survival and population declines relative to control populations. Quoll-invaded populations (n = 4) were also significantly shyer than nearby, quoll-free populations (n = 3) of conspecifics. This rapid but generalised response to a novel threat was replaced over the following two years with more threat-specific antipredator behaviours (i.e. predator-scent aversion). Predator-exposed populations, however, remained more neophobic than predator-free populations throughout the study. These behavioural responses manifested rapidly in avoidance of seeds associated with quoll scent, with discrimination playing out over a spatial scale of tens of metres. Presumably the significant and novel predation pressure induced by quolls drove melomys populations to fine-tune behavioural responses to be more predator-specific through time. These behavioural shifts could reflect individual plasticity (phenotypic flexibility) in behaviour or may be adaptive shifts from natural selection imposed by quoll predation. Our study provides a rare insight into the rapid ecological and behavioural shifts enacted by prey to mitigate the impacts of a novel predator and shows that trophic cascades can be strongly influenced by behavioural changed rates of seed predation by melomys across treatments. Quoll-invaded melomys populations exhibited lower per-capita seed take rates, and rapidly developed an as well as numerical responses.

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Jolly, C. J., Smart, A. S., Moreen, J., Webb, J. K., Gillespie, G. R., Phillips, B. L.. 2019-11-27. Trophic cascade driven by behavioural fine-tuning as naive prey rapidly adjust to a novel predator. https://doi.org/10.1101/856997

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