Top predators cause avoidance behaviours in competitors and prey, which can lead to niche partitioning and facilitate coexistence. We investigate changes in partitioning of the temporal niche in a mammalian community in response to both the rapid decline in abundance of a top predator and its rapid increase, produced by two concurrent natural experiments: 1) the severe decline of the Tasmanian devil due to a transmissible cancer, and 2) the introduction of Tasmanian devils to an island, with subsequent population increase. We focus on devils, two mesopredators, and three prey species, allowing us to examine niche partitioning in the context of intra- and inter-specific competition, and predator-prey interactions. The most consistent shift in temporal activity occurred in devils themselves, which were active earlier in the night at high densities, presumably because of heightened intraspecific competition. When devils were rare, their closest competitor, the spotted-tailed quoll, increased activity in the early part of the night, resulting in increased overlap with the devil’s temporal niche and suggesting release from interference competition. The invasive feral cat, another mesopredator, did not shift its temporal activity in response to either decreasing or increasing devil densities. Shifts in temporal activity of the major prey species of devils were stronger in response to rising than to falling devil densities. We infer that the costs associated with not avoiding predators when their density is rising (i.e., death) are higher than the costs of continuing to adopt avoidance behaviours as predator densities fall (i.e., loss of foraging opportunity), so rising predator densities may trigger more rapid shifts. The rapid changes in devil abundance provide a unique framework to test how the non-lethal effects of top predators affect community-wide partitioning of temporal niches, revealing that this top-predator has an important but varied influence on the diel activity of other species.
Temporal overlap: top-predator decline
Camera data used to analyse changes in temporal activity on the Tasmanian mainland in response to Tasmanian devil population declines. This data file was used in the analysis of circular overlap, and was used to produce the left column of Figure 2 from our paper in Ecography. See README for details about variables.
overlapData_decliningDevil_Ecography.csv
Temporal overlap: top-predator introduction
Camera data used to analyse changes in temporal activity following the introduction of Tasmanian devils to Maria Island. This data file was used in the analysis of circular overlap, and was used to produce the right column of Figure 2 from our paper in Ecography. See README for details about variables.
overlapData_increasingDevil_Ecography.csv
Changes in Tasmanian devil temporal activity following population decline
Changes in Tasmanian devil temporal activity following severe population declines.Camera data was analysed using a GAM to produce Fig 3A of our paper in Ecography. Tasmanian devil records at each site were binned into the nearest hourly bin i.e. there was a total of 24 bins. We then calculated the proportion of total activity in each hour of the day for each site. See paper for details.
devilTemporalActivity_GAM_decliningDevil.csv
Changes in spotted-tailed quoll temporal activity
Changes in spotted-tailed quoll temporal activity following the decline of Tasmanian devils. This camera data was analysed using a GAM to produce Fig 3B of our paper in Ecography. Spotted-tailed quoll records at each site were binned into the nearest hourly bin i.e. there was a total of 24 bins. We then calculated the proportion of total activity in each hour of the day for each site. See paper for details.
quollTemporalActivity_GAM.csv
Changes in Tasmanian devil temporal activity following increase in density
Changes in Tasmanian devil temporal activity following the introduction of Tasmanian devils to Maria Island ("MI"), compared to a control site ("C"). This camera data was analysed using a GAM to produce Fig 3C of our paper in Ecography. Devil records at each site were binned into the nearest hourly bin i.e. there was a total of 24 bins. We then calculated the proportion of total activity in each hour of the day for each site. See paper for details.
devilTemporalActivity_GAM_increasingDevil.csv
Changes in Bennett's wallaby temporal activity following increase in top-predator density
Changes in Bennett's wallaby temporal activity following the introduction of Tasmanian devils to Maria Island ("MI"), compared to a control site ("C"). This camera data was analysed using a GAM to produce Fig 3D of our paper in Ecography. Wallaby records at each site were binned into the nearest hourly bin i.e. there was a total of 24 bins. We then calculated the proportion of total activity in each hour of the day for each site. See paper for details.
wallabyTemporalActivity_GAM.csv