1)Question/attack: "Nature is cruel--cats will play with their food--so we should be cruel too. It's survival of the fittest. Compassion is not natural, and other species are motivated by self interest. "  

Response: a) "survival of the fittest" would allow one to exploit and enslave other humans . You acknowledge that one animal will prey on another, but you ignore that they can also prey on members of their own species--in which case, by using this moral standard and policy, humans preying on other humans would be justified too.

Response: b)a domestic cat is fed, and has no predators. A wild cat has to be on guard for competitors. Not catching prey means not eating. The time for playing with their food would be greatly diminished. More importantly, there is no evidence that a cat is aware of the mouse's suffering and takes pleasure from that fact-like humans have been known to do. There are hunters who enjoy killing animals.

  Response: c) Speciesists who use this attack contradict themselves—for while they say that species have a natural tendency to stick together,  they will also allege that it’s a "dog eat dog" world, compassion is not natural, and other species are motivated by self interest! In fact, other species have been known to exhibit altruism. Bats will lend food to other bats, ducks have been known to feign injury to lure a predator away from the flock. There are instances of domestic animals "adopting" the offspring of other species, and dogs rescuing humans.  Feral children found living with wolves in the wild etc. And conversely, there are instances where humans have risked their own lives to help a member of another species.

Response: d) The very fact that the concept of animal rights is accepted by some shows that there is no overriding biological drive in humans to "stick together"  or avoid compassion for members of other species.

Response: e) There was an experiment conducted where monkeys were starved unless they pressed a button that would release food--AND torture a monkey wired to shock devices. It was found that the monkeys preferred to endure starvation rather than inflict pain on another--the exact opposite response anticipated by the scientists. Yet a similar experiment involving humans where neither subjects were truly being tortured(unlike the monkeys) found that most of the humans were willing to see another human suffer--just to avoid displeasing the individual giving them the orders.