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Jon Cox

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Cats pose a serious threat to biodiversity: Why do we accept it? What should be done?

According to the ASPCA, there are around 90 million owned domestic cats (Felis catus) in the U.S., and taking into account strays and feral cats, the total number is estimated to be as high as 160 million (1). Loss et al. (2013) estimates that cats roaming outdoors kill 1.4-­3.7 BILLION birds and 6.9­-20.7 BILLION mammals in the U.S. annually (2). Reptiles and amphibians such as snakes, lizards, frogs, etc., are also frequently killed by cats.

Cats are even more popular New Zealand, where they are contributing to declines of endemic birds such as the critically endangered kakapo (3), which have evolved in the absence of predators. Businessman/philanthropist Gareth Morgan is trying to gather support for legislation that would aggressively deal with stray and feral cats and potentially eliminate cats from New Zealand to take pressure off of threatened species (4 & 5). With Morgan’s plan, in addition to regulation that would reduce cat populations and increase owner accountability, residents would be encouraged to not replace their cats. As of now the majority of New Zealanders surveyed are in opposition to Morgan’s initiative.

Would a proposition like Morgan’s meet similar resistance in the U.S.? Probably, but is he on the right track? Would you personally support something like it for your state or country? Why or why not is it a good idea? Is this type of legislation necessary to curb the problem and protect wildlife? If you disagree, what are some alternatives? Will the aesthetics and familiarity of cats keep them off limits to such ideas in the opinions of the general public?

1. http://www.aspca.org/about-us/faq/pet-statistics.aspx
2. http://www.abcbirds.org/abcprograms/policy/cats/pdf/Loss_et_al_2013.pdf
3. http://www.avianweb.com/kakapo.html
4. http://www.npr.org/blogs/thetwo-way/2013/01/24/170191917/new-zealand-environmentalist-wants-to-eliminate-cats-to-save-birds
5. http://www.livescience.com/26525-cat-eradication-new-zealand-save-birds.html


Closing Statement from Jon Cox

Thanks to everyone who contributed to a thought provoking discussion!

I think we can all agree that we need to be responsible with our pets! For the sake of ecological and human health. And pet owners must realize that their carelessness is costly. Plans to completely eliminate cats from areas where they are very popular are pretty far fetched, but stricter regulation is a must, and domestic cats do NOT belong in the wild, period. Feral cats need to be seen and dealt with just as any other invasive species. However, extreme caution is necessary in any attempt to remove them where they have become established as a keystone species.

Check out Australian cat laws for a look at the legislation adopted by a people who cherish their native wildlife and do not want to see it be destroyed by invasives.

And lastly, we must keep in mind that invasive species are just one way in which we threaten biodiversity. Overexploitation and especially habitat loss pose even greater threats to species survival.

Thanks again!


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    Mario R

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    May 7 2013: I found an interesting article that highlighted the effects of reducing predatory effects in ecosystems. The article was talking about predatory chains and how the elimination of a top, or superpredator, might open the door for a different predator, or mesopredator, to take the original predator's place. This would in fact lead to the extinction of the prey. The example they looked at was an endemic bird population, and the superpredator were feral domestic cats.

    This got me to thinking about the effects of suppressing cats' activities outdoors. If something was done to regulate cats' outdoor liberties, would there be increases in predatory activity of a different species on the same prey?

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      May 7 2013: Great point as usual, Mario.

      That was exactly the same line of thought that I was mulling over. For as long as there have been modern urban and suburban areas there have been cats present really. So I think it makes sense to think about it as though those environments and cats have co-evolved in a way. That means we have no real way of knowing what will happen if cats are eliminated from an area all together. Sure we can speculate that maybe those species preyed upon by the cats in those environments will recover greatly, but what's to say that some other species wouldn't come in to fill that niche vacated by the cats? The reality is that we really don't know what will happen until it does, and this unpredictability is why removal experiments are often so dangerous.

      The article Mario linked makes the good point that other predators often move in to such situations quickly, and in particular uses the example of rodents coming in to prey on the eggs of birds usually targeted by feral cats. I was able to find some more articles that addressed this phenomena of top predator removal harming an ecosystem overall, and I think they would be valuable to take a look at as it is a really counterintuitive but interesting viewpoint.

      1. http://rspb.royalsocietypublishing.org/content/276/1671/3249.short
      2. http://www.sciencedirect.com/science/article/pii/S0169534701021942
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        May 7 2013: Great point about urban/suburban environments co-evolving with cats present!
        Even in rural areas, as some have pointed out, farmers really need cats for pest control, and in America I don't really think cats can cause even a fraction of the damage they can cause in island environments. North America has always had plenty of predators that have interacted and co-evolved with potential prey species, whereas in New Zealand (and many other island nations) there have NEVER been endemic mammalian predators present for things to evolve defenses for, and such an introduction can vastly destabilize a system, even leading to extinction in some cases. The only predator i can find ever being from New Zealand was Haast's eagle which humans also drove to extinction, which, due to its diet of moa and corresponding huge size, was likely not a large source of predation for many of these smaller birds anyway- they were completely defenseless.
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      May 7 2013: What will be the predator that will partially fill the void of the cat superpredator? I ask this, for in many environments, cats are introduced, so they take advantage prey that have no natural predators or inefficient natural predators.

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