Amplified predation after fire suppresses rodent populations in Australia’s tropical savannas
Lily Leahy A , Sarah M. Legge B C , Katherine Tuft B , Hugh W. McGregor A B , Leon A. Barmuta A , Menna E. Jones A and Christopher N. Johnson A D
+ Author Affiliations
- Author Affiliations
A School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, Tas. 7001, Australia.
B Australian Wildlife Conservancy, Mornington Sanctuary, Derby, WA 6728, Australia.
C Present address: National Environmental Science Program Threatened Species recovery Hub, Centre for Biodiversity and Conservation Science, University of Queensland, St Lucia, Qld 4072, Australia.
D Corresponding author. Email: c.n.johnson@utas.edu.au
Wildlife Research 42(8) 705-716 https://doi.org/10.1071/WR15011
Submitted: 20 January 2015 Accepted: 23 November 2015 Published: 17 February 2016
Abstract
Context: Changes in abundance following fire are commonly reported for vertebrate species, but the mechanisms causing these changes are rarely tested. Currently, many species of small mammals are declining in the savannas of northern Australia. These declines have been linked to intense and frequent fires in the late dry season; however, why such fires cause declines of small mammals is unknown.
Aims: We aimed to discover the mechanisms causing decline in abundance of two species of small mammals, the pale field rat, Rattus tunneyi, and the western chestnut mouse, Pseudomys nanus, in response to fire. Candidate mechanisms were (1) direct mortality because of fire itself, (2) mortality after fire because of removal of food by fire, (3) reduced reproductive success, (4) emigration, and (5) increased mortality because of predation following fire.
Methods: We used live trapping to monitor populations of these two species under the following three experimental fire treatments: high-intensity fire that removed all ground vegetation, low-intensity fire that produced a patchy burn, and an unburnt control. We also radio-tracked 38 R. tunneyi individuals to discover the fates of individual animals.
Key results: Abundance of both species declined after fire, and especially following the high-intensity burn. There was no support for any of the first four mechanisms of population decline, but mortality owing to predation increased after fire. This was related to loss of ground cover (which was greater in the high-intensity fire treatment), which evidently left animals exposed to predators. Also, local activity of two predators, feral cats and dingoes, increased after the burns, and we found direct evidence of predation by feral cats and snakes.
Conclusions: Fire in the northern savannas has little direct effect on populations of these small mammals, but it causes declines by amplifying the impacts of predators. These effects are most severe for high-intensity burns that remove a high proportion of vegetation cover.
Implications: To prevent further declines in northern Australia, fire should be managed in ways that limit the effects of increased predation. This could be achieved by setting cool fires that produce patchy burns, avoiding hot fires, and minimising the total area burnt.
Additional keywords: Canis lupus dingo, Felis catus, fire ecology, northern Australia, prescribed burning, Pseudomys nanus, Rattus tunneyi, small mammals.
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