Rabid hatred of an animal species often leads do-gooders to spread havoc on nature. In particular, hatred of cats is frequent in the Anglo-Saxon world, for a number of psychological reasons which cannot be addressed here. The ethical aspects of this hatred are striking, but one should also be aware of the ecological impact of this hatred of a beautiful product of millions of years of evolution. Here’s one example.
Dr Gabriel Bittar, Kangaroo Island
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Indirect effects of invasive species removal devastate World Heritage Island http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2664.2008.01601.x/full
DOI: 10.1111/j.1365-2664.2008.01601.x
Management implications of the Macquarie Island trophic cascade revisited: a reply to Dowding et al. (2009)
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2664.2009.01708.x/full
by Bergstrom et al. 2009
J. of Applied Ecology
Volume 46, Issue 1
February 2009
Pages 73–81 and 1133–1136
Extracts:
Macquarie Island (54°30′S, 158°57′E) is an oceanic island in the sub-Antarctic region . Low-lying, 34 km long and with a cool, maritime climate, it is covered in tundra-like vegetation, featuring tussock grasses, megaherbs and bryophytes
(…) Following eradication of cats Felis catus in 2001, rabbit Oryctolagus cuniculus numbers increased substantially although a control action was in place (Myxoma virus), resulting in island-wide ecosystem effects.
(…) on New Zealand’s Little Barrier Island, removal of cats resulted in reduced breeding success of Cook’s petrel Pterodroma cookii, which only increased following rat eradication (Rayner et al. 2007)
(…) Here, we combine population data on invasive herbivorous rabbits Oryctolagus cuniculus (L.), plot-scale vegetation analyses, climate analysis and landscape change detection techniques using satellite imagery, to show how a local management intervention, the eradication of feral cats Felis catus L., has precipitated a trophic cascade leading to rapid, landscape-wide ecosystem changes on sub-Antarctic Macquarie Island. Specifically, we first review evidence demonstrating that cats consumed substantial numbers of rabbits prior to their eradication. Next, we show that since the eradication of cats, rabbit numbers on the island have increased significantly. We then provide evidence of impacts of rabbits on vegetation via grazing, at both plot and landscape scale between 2000 and 2007, which cannot be attributed to other causes, such as climate change or seasonal variation. In combination, these data demonstrate that the removal of cats has resulted in an increase in rabbit abundance, which has led to substantial local and landscape-scale changes in vegetation.
(…) Management of rabbits commenced in 1968 with the introduction of the European rabbit flea Spilopsyllus cuniculi (vector of the Myxoma virus)
(…) A cat eradication programme commenced in 1985 and was expanded in 1998. Between 1985 and 1995, approximately 124 cats were killed per year and it was estimated that the recruitment rate matched the kill rate. The eradication rate increased to c. 220 cats per year for the next 3 years, dropping to 99 cat kills in 1999, and a single cat (the last cat) shot in 2000. Rabbit numbers then increased rapidly, and in a little more than 5 years, they have substantially altered large areas of the island (Scott & Kirkpatrick 2008)
(…) Indeed, it appears that Costin & Moore’s (1960) prediction that the ‘vegetation on Macquarie Island is doomed to destruction’ is rapidly being realized.
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In Bergstrom et al.’s (2009) study, we demonstrated that feral cats Felis catus on sub-Antarctic Macquarie Island were exerting top-down control 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.
(…) 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.
(…) Rather, it appears that the prevailing view was very similar to that held by Dowding et al. (2009) – that although some top-down control by cats may have been taking place, it was relatively unimportant. Our analyses suggest otherwise. In conclusion, we stand by our earlier statements. Our new analyses also provide further grounds for doing so.
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Addendum by Dr Gabriel Bittar, 2015.02.02
A study by Doherty et al. 2015, “A continental-scale analysis of feral cat diet in Australia”, published in Journal of Biogeography, 2015.02.02, DOI: 10.1111/jbi.12469, demonstrates that wherever there are rabbits in Australia, these are the main prey of feral cats, and that any local extermination of rabbits has the consequence of forcing local cats to switch to marsupials and reptiles.
Another reminder that ecosystems have their logic of checks and balance, that it is generally imprudent to tinker with them, and that hell is paved with good intentions.
There are no rabbits on Kangaroo Island, but there are many murines (rats and mice), which are the main prey of the island feral cats. The eradication of murines is not envisageable from a practical point of view, but there are plans to do it the other way round: to exterminate… their main predators, the feral cats ! Considering that rats are well established about everywhere on the island, and that they have a very high rate of reproduction, it’s obvious that they would gain immediately from any extermination of the island’s feral cats. And considering that rats are predatory, the local birds and marsupials would find themselves worse off on the whole…
Further readings:
Domestic cats – wildlife enemy number one or convenient scapegoats ? – Hartwell 2004
Without feral cats, Kangaroo Island would be a Rat Island — Dr G. Bittar 2013.09.30
Feral cats of Kangaroo Island are part of its ecosystem — Dr Bittar, 2015.04.15