Predation by introduced foxes on native bush rats in Australia: do foxes take the doomed surplus?

Predation by introduced foxes on native bush rats in Australia: do foxes take the doomed surplus? Summary 1. Introduced vertebrate predators are one of the most important threats to endemic mammal species. Prey naivety can lead to heavy losses to alien predators, which may be additive to ‘natural’ sources of mortality that limit prey populations. Alternatively, predators may take only individuals that are surplus to the population, and hence predator control may have little benefit for susceptible native prey populations. 2. A field‐based predator removal experiment was used to test the predator limitation and doomed surplus hypotheses on the impact of introduced red foxes Vulpes vulpes on populations of native bush rats Rattus fuscipes in south‐eastern Australia. 3. Poison baiting was used in July 1993 to reduce fox numbers in two fox‐removal sites from 2·8–3·4 km–1 (spotlight counts) to less than 0·5 km–1 within 6 months. Fox density in two non‐removal sites remained typically five times higher than that in removal sites. 4. Bush rat numbers on replicated trapping plots showed no response to fox removal, and rodent numbers fluctuated seasonally in all sites over 22 months of fox control, which represented two breeding seasons for rats. 5. Fox removal also had no effect on rat persistence time, adult body weight, captures of juveniles or immature animals during the breeding season, nor captures of immigrant or transient animals. 6. The general lack of response by rat populations to fox removal supported the doomed surplus hypothesis, that fox predation operated as a compensatory source of mortality rather than an additive one. Consequently, there was no measured benefit to native rat populations of intensive short‐term fox control. 7. The results suggest that where predation pressure is low, not all predation mortality will be additive to prey populations even if it results from a predator introduced to the ecosystem. Hence, indiscriminate control of introduced predators is unlikely to produce uniform benefits for all the species they prey upon. Feral predator control should therefore be targeted for native species known to be predation limited or for species where any mortality threatens persistence. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Applied Ecology Wiley

Predation by introduced foxes on native bush rats in Australia: do foxes take the doomed surplus?

Journal of Applied Ecology, Volume 36 (6) – Dec 1, 1999

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Publisher
Wiley
Copyright
Copyright © 1999 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0021-8901
eISSN
1365-2664
D.O.I.
10.1046/j.1365-2664.1999.00463.x
Publisher site
See Article on Publisher Site

Abstract

Summary 1. Introduced vertebrate predators are one of the most important threats to endemic mammal species. Prey naivety can lead to heavy losses to alien predators, which may be additive to ‘natural’ sources of mortality that limit prey populations. Alternatively, predators may take only individuals that are surplus to the population, and hence predator control may have little benefit for susceptible native prey populations. 2. A field‐based predator removal experiment was used to test the predator limitation and doomed surplus hypotheses on the impact of introduced red foxes Vulpes vulpes on populations of native bush rats Rattus fuscipes in south‐eastern Australia. 3. Poison baiting was used in July 1993 to reduce fox numbers in two fox‐removal sites from 2·8–3·4 km–1 (spotlight counts) to less than 0·5 km–1 within 6 months. Fox density in two non‐removal sites remained typically five times higher than that in removal sites. 4. Bush rat numbers on replicated trapping plots showed no response to fox removal, and rodent numbers fluctuated seasonally in all sites over 22 months of fox control, which represented two breeding seasons for rats. 5. Fox removal also had no effect on rat persistence time, adult body weight, captures of juveniles or immature animals during the breeding season, nor captures of immigrant or transient animals. 6. The general lack of response by rat populations to fox removal supported the doomed surplus hypothesis, that fox predation operated as a compensatory source of mortality rather than an additive one. Consequently, there was no measured benefit to native rat populations of intensive short‐term fox control. 7. The results suggest that where predation pressure is low, not all predation mortality will be additive to prey populations even if it results from a predator introduced to the ecosystem. Hence, indiscriminate control of introduced predators is unlikely to produce uniform benefits for all the species they prey upon. Feral predator control should therefore be targeted for native species known to be predation limited or for species where any mortality threatens persistence.

Journal

Journal of Applied EcologyWiley

Published: Dec 1, 1999

References

  • Teaching an endangered mammal to recognise predators
    McLean, McLean; Lundie‐Jenkins, Lundie‐Jenkins; Jarman, Jarman
  • Effects of vertebrate predation on a caviomorph rodent, the degu ( Octodon degus ), in a semiarid thorn scrub community in Chile
    Meserve, Meserve; Gutierrez, Gutierrez; Jaksic, Jaksic
  • Effects of predator removal on vertebrate prey populations: birds of prey and small mammals
    Norrdahl, Norrdahl; Korpimäki, Korpimäki
  • Limits to predator regulation of rabbits in Australia: evidence from predator‐removal experiments
    Pech, Pech; Sinclair, Sinclair; Newsome, Newsome; Catling, Catling
  • Predation, competition and prey communities: a review of field experiments
    Sih, Sih; Crowley, Crowley; McPeek, McPeek; Petranka, Petranka; Strohmeier, Strohmeier
  • Patterns and causes of extinction and decline in Australian Conilurine rodents
    Smith, Smith; Quin, Quin

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