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Abstract

1. The management of non-indigenous species is not without its complications. In Bergstromet al.’s
(2009) study, we demonstrated that feral cats Felis catus on sub-Antarctic Macquarie Island were
exerting top-downcontrol on the feral rabbit Oryctolagus cuniculus population, and that the eradication
of the cats led to a substantial increase in rabbit numbers and an associated trophic cascade.
2. Dowding et al. (2009) claim our modelling was flawed for various reasons, but primarily that a
reduction in the application of the rabbit control agent,Myxoma virus, coinciding with cat removal,
was a major driver of rabbit population release.
3. We explore this proposition (as well as others) by examining rates of Myxoma viral release
between 1991 and 2006 (with an attenuation factor for the years, 2003–2006) in association with
presence ⁄ absence of cats against two estimates of rabbit population size. Myxoma viral release was
a significant factor in the lower estimates of rabbit population, but the effect was small, and was not
significant for higher rabbit population estimates. By contrast, the presence or absence of cats
remained highly significant for both estimates.
4. Synthesis and applications. We re-affirm our position that top-down control of rabbit numbers
by cats, prior to their eradication, was occurring on Macquarie Island. Nonetheless, we agree with
Dowding et al. (2009) that systems with multiple invasive species represent complex situations that
require careful scrutiny. Such scrutiny should occur in advance of, during, and following management
interventions.

Item Type:	Article
Authors/Creators:	Bergstrom, DM and Lucieer, A and Kiefer, K and Wasley, J and Belbin, L and Pederson, T and Chown, SL
Keywords:	invasive species • rabbits • sub-Antarctic • trophic cascade
Journal or Publication Title:	Journal of Applied Ecology
ISSN:	0021-8901
DOI / ID Number:	10.1111/j.1365-2664.2009.01708.x
Additional Information:	The original publication is available at http://www.interscience.wiley.com/
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