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Devil declines and catastrophic cascades: is mesopredator release of feral cats inhibiting recovery of the eastern quoll?

Fancourt BA, Hawkins CE, Cameron EZ, Jones ME, Nicol SC - PLoS ONE (2015)

Bottom Line: This decline has been linked to a period of unfavourable weather, but subsequent improved weather conditions have not been matched by quoll recovery.We did not find evidence of a negative relationship between devil and cat abundance, nor of higher cat abundance in areas where devil populations had declined the longest.Temporal overlap in observed cat and quoll activity was higher in summer than in winter, but this seasonal difference was unrelated to devil declines.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Tasmania, Hobart, Tasmania, Australia.

ABSTRACT
The eastern quoll (Dasyurus viverrinus) is a medium-sized Australian marsupial carnivore that has recently undergone a rapid and severe population decline over the 10 years to 2009, with no sign of recovery. This decline has been linked to a period of unfavourable weather, but subsequent improved weather conditions have not been matched by quoll recovery. A recent study suggested another mechanism: that declines in Tasmanian devil (Sarcophilus harrisii) populations, due to the spread of the fatal Devil Facial Tumour Disease, have released feral cats (Felis catus) from competitive suppression, with eastern quoll declines linked to a subsequent increase in cat sightings. Yet current evidence of intraguild suppression among devils, cats and quolls is scant and equivocal. We therefore assessed the influences of top-down effects on abundance and activity patterns among devils, feral cats and eastern quolls. Between 2011 and 2013, we monitored four carnivore populations using longitudinal trapping and camera surveys, and performed camera surveys at 12 additional sites throughout the eastern quoll's range. We did not find evidence of a negative relationship between devil and cat abundance, nor of higher cat abundance in areas where devil populations had declined the longest. Cats did not appear to avoid devils spatially; however, there was evidence of temporal separation of cat and devil activity, with reduced separation and increasing nocturnal activity observed in areas where devils had declined the longest. Cats and quolls used the same areas, and there was no evidence that cat and quoll abundances were negatively related. Temporal overlap in observed cat and quoll activity was higher in summer than in winter, but this seasonal difference was unrelated to devil declines. We suggest that cats did not cause the recent quoll decline, but that predation of juvenile quolls by cats could be inhibiting low density quoll populations from recovering their former abundance through a 'predator pit' effect following weather-induced decline. Predation intensity could increase further should cats become increasingly nocturnal in response to devil declines.

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Related in: MedlinePlus

Overlap of eastern quoll and feral cat daily activity from statewide camera survey sites.Sites categorised as high (n = 5 sites) or low (n = 7) quoll abundance as per Table 2. Plots show overlap of quoll (EQ, black solid line) and cat (CAT, blue dashed line) activity. Sample sizes in parentheses indicate number of detection events for each species. Grey shading indicates the amount of temporal activity overlap between quolls and cats.
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pone.0119303.g007: Overlap of eastern quoll and feral cat daily activity from statewide camera survey sites.Sites categorised as high (n = 5 sites) or low (n = 7) quoll abundance as per Table 2. Plots show overlap of quoll (EQ, black solid line) and cat (CAT, blue dashed line) activity. Sample sizes in parentheses indicate number of detection events for each species. Grey shading indicates the amount of temporal activity overlap between quolls and cats.

Mentions: Quoll activity was strictly nocturnal at all statewide camera sites, however the temporal activity profiles differed between high and low quoll sites (Fig. 7). At high quoll sites, activity peaked following sunset, and quolls remained fairly active until sunrise. At low quoll sites, the peak following sunset was notably absent, and activity peaked around midnight. Cats were active across both day and night, with a similar activity peak around sunset at both high and low quoll sites (Fig. 7). Differences in cat and quoll activity were evident at both high (W = 6.42, P = 0.040) and low quoll sites (W = 40.20, P < 0.001). There was increased total overlap between cat and quoll activity at high quoll sites (Δ1 = 0.62 (95% CI: 0.46–0.76)) compared to low quoll sites (Δ1 = 0.48 (95% CI: 0.31–0.57)).


Devil declines and catastrophic cascades: is mesopredator release of feral cats inhibiting recovery of the eastern quoll?

Fancourt BA, Hawkins CE, Cameron EZ, Jones ME, Nicol SC - PLoS ONE (2015)

Overlap of eastern quoll and feral cat daily activity from statewide camera survey sites.Sites categorised as high (n = 5 sites) or low (n = 7) quoll abundance as per Table 2. Plots show overlap of quoll (EQ, black solid line) and cat (CAT, blue dashed line) activity. Sample sizes in parentheses indicate number of detection events for each species. Grey shading indicates the amount of temporal activity overlap between quolls and cats.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4356622&req=5

pone.0119303.g007: Overlap of eastern quoll and feral cat daily activity from statewide camera survey sites.Sites categorised as high (n = 5 sites) or low (n = 7) quoll abundance as per Table 2. Plots show overlap of quoll (EQ, black solid line) and cat (CAT, blue dashed line) activity. Sample sizes in parentheses indicate number of detection events for each species. Grey shading indicates the amount of temporal activity overlap between quolls and cats.
Mentions: Quoll activity was strictly nocturnal at all statewide camera sites, however the temporal activity profiles differed between high and low quoll sites (Fig. 7). At high quoll sites, activity peaked following sunset, and quolls remained fairly active until sunrise. At low quoll sites, the peak following sunset was notably absent, and activity peaked around midnight. Cats were active across both day and night, with a similar activity peak around sunset at both high and low quoll sites (Fig. 7). Differences in cat and quoll activity were evident at both high (W = 6.42, P = 0.040) and low quoll sites (W = 40.20, P < 0.001). There was increased total overlap between cat and quoll activity at high quoll sites (Δ1 = 0.62 (95% CI: 0.46–0.76)) compared to low quoll sites (Δ1 = 0.48 (95% CI: 0.31–0.57)).

Bottom Line: This decline has been linked to a period of unfavourable weather, but subsequent improved weather conditions have not been matched by quoll recovery.We did not find evidence of a negative relationship between devil and cat abundance, nor of higher cat abundance in areas where devil populations had declined the longest.Temporal overlap in observed cat and quoll activity was higher in summer than in winter, but this seasonal difference was unrelated to devil declines.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Tasmania, Hobart, Tasmania, Australia.

ABSTRACT
The eastern quoll (Dasyurus viverrinus) is a medium-sized Australian marsupial carnivore that has recently undergone a rapid and severe population decline over the 10 years to 2009, with no sign of recovery. This decline has been linked to a period of unfavourable weather, but subsequent improved weather conditions have not been matched by quoll recovery. A recent study suggested another mechanism: that declines in Tasmanian devil (Sarcophilus harrisii) populations, due to the spread of the fatal Devil Facial Tumour Disease, have released feral cats (Felis catus) from competitive suppression, with eastern quoll declines linked to a subsequent increase in cat sightings. Yet current evidence of intraguild suppression among devils, cats and quolls is scant and equivocal. We therefore assessed the influences of top-down effects on abundance and activity patterns among devils, feral cats and eastern quolls. Between 2011 and 2013, we monitored four carnivore populations using longitudinal trapping and camera surveys, and performed camera surveys at 12 additional sites throughout the eastern quoll's range. We did not find evidence of a negative relationship between devil and cat abundance, nor of higher cat abundance in areas where devil populations had declined the longest. Cats did not appear to avoid devils spatially; however, there was evidence of temporal separation of cat and devil activity, with reduced separation and increasing nocturnal activity observed in areas where devils had declined the longest. Cats and quolls used the same areas, and there was no evidence that cat and quoll abundances were negatively related. Temporal overlap in observed cat and quoll activity was higher in summer than in winter, but this seasonal difference was unrelated to devil declines. We suggest that cats did not cause the recent quoll decline, but that predation of juvenile quolls by cats could be inhibiting low density quoll populations from recovering their former abundance through a 'predator pit' effect following weather-induced decline. Predation intensity could increase further should cats become increasingly nocturnal in response to devil declines.

Show MeSH
Related in: MedlinePlus