You have to differentiate between (1) wild cats and (2) domestic, stray and feral cats. I will deal with (2) first.
Domestic, stray and feral cats
I’d predict that if there were no cats whatsoever the change in the world by there being no domestic, stray and feral cats would be larger than if there were no wild cats. This is because there are about 500 million domestic, stray and feral cats whereas the total number of wild cats of all species is a fraction of this. Although the big cats are top predators, which is important. Their numbers are small, however.
Between domestic, stray and feral cats the biggest impact on the world is from feral cats. They have to survive independently of people. They have to kill prey. It is this aspect of their lives which quietly, behind the scenes, affects us. Let’s say that there are about 300 million feral cats on the planet. What do they eat? It depends where they live but let’s look at three places.
In Victoria, Australia a study analysed the stomach contents of 80 feral cats by percentage volume and percentage occurrence in primary and secondary habitats. Their prey items were rabbit, mouse, ringtail possum, other, Phalanger (a genus of possums), murids, insects, birds, lizards, frogs and carrion (and household scraps).
In Europe and North America it must depend upon the location once again. Studies of feral cats in California found that the major dietary component was voles. In Wisconsin voles were also the main prey. House mice, deer mice, rabbits and brown rats were also important in Wisconsin. Adult rats are too difficult for many feral cats. They normally prey on juvenile or sub-adult rats. In a village in Bedfordshire, UK, wood mice, bank voles, field voles, common shrews, pygmy shrews and rabbits were also eaten. The house sparrow, song thrush, blackbird, robin and other birds were also eaten.
In New Zealand the diet of feral cats was studied by Fitzgerald and Karl in the Orongoro Valley. Black rats were the most important prey item at 42% by weight. Then rabbits, bushtail possums, house mice and stoats were popular. Birds made up about 4.5% by weight of their diet and insects made up about 2% of their diet.
I think you can see a general trend amongst the studies. Feral cats eat a lot of rodents, small mammals such as mice, voles and also rabbits. Then birds too but they’re well down the list and reptiles as well. Without feral cats on the planet there would be a lot more of these prey animals and the government and local authorities would have to initiate programs of extermination of these rodents as opposed to a programme of extermination of feral cats which takes place in Australia. Ornithologists would be in heaven because their birds would no longer be threatened by feral cats. Local authorities in the US would have one less problem on their plates but they would possible have two more new ones.
Domestic and stray cats have a similar diet if they hunt. But although they have a substantial impact it is less than that of feral cats. Without cats being in the ecosystem in which they are firmly embedded there would be many more small mammals primarily and reptiles and birds secondarily. We would notice it and it could cause a big problem. Feral cats are part of the ecosystem.
P.S. Domestic cats affect the environment as millions of tons of clay cat litter is mined and then reburied with cat poop. This affects the planet negatively. Domestic cats eat (in heavily processed commercial cat food) millions of tons of road kill animals, diseased livestock and euthanised cats and dogs at shelters. All this would stop. There’d be real issues, some beneficial and some not. Veterinarians would probably temporarily go out of business as a big chunk of it would be missing.
The wild cat species are in quite small numbers as mentioned. There are about 3,500 tigers and about 20,000 lions on the planet. Some small cat species such as the Andean Mountain cat are also in decline and in small numbers, about 2,000. We don’t even know how many servals there are but it will be around 20,000 at a guess or less. Relatively, these are small numbers and their impact on the planet is quite small accordingly. There is a huge conflict between the big wild cat species and humans because humans farm on the territory that was once “owned” by the big cats. A lot of the farmers would be pleased if there were no big cats. The rest of the world would be displeased and many would be shocked. If there were no iconic cats such as tigers and lions on the planet it would be a far less beautiful place.
The lions of Africa sometimes attack livestock. But by and large they eat large prey animals such as zebra, wildebeest, impala and buffalo. Without the lion these animals would be more numerous. But as mentioned, the lion population is relatively small at 20,000 and therefore their impact is being diminished year-on-year. They have become an iconic species to be looked at by tourists and photographed. Their imprint on the planet is far less than it was over 100 years ago.
However, as the big cats are top predators there would also be a change to ecosystems. I’ll provide one example from a study published on July 14, 2011 and carried out by Stony Brook University. They say, “the decline of large predators and herbivores in all regions of the world is causing substantial changes to Earth’s terrestrial, freshwater, and marine ecosystems.
The reduction of lions and leopards from areas of sub-Saharan Africa caused the baboon population to swell. This unexpectedly increased transmission of intestinal parasites from baboons to humans as the primates were forced to forage closer to human settlements.
As for the small and medium-sized wild cats once again without them there would be a loss to the planet’s fauna and biodiversity. That’s the main downside. Loss of prey animals is a minor affair relatively. Although some small wild cat species compete with humans for bush meat. Human successfully kill the prey animals of small wild cats. There is less prey animals for them. Without cats humans would more able to kill bushmeat without competition.
As an after thought you have to throw in the fact that there would be no zoos, no chance of the citizens of China eating tiger penises to improve their erections and tiger bones for some other weird reason. There would be no persecution of the wild cats anymore. It would be over. Thanks be to God.
I can foresee a big rodent pest control problem without cats. That’s my overriding impression. Can you contribute to the debate in a comment? These are simply my thoughts. They are not set in concrete.