Survival of the fittest, adapting and adapting to others' adaptations, all a part of evolution . . . so cool.
I don't see Andalites swimming a whole lot to be endangered by that thingy though, also wolves aren't around just because they're canny (that's the Coyote) they're around because at some point we realized that killing every last one of them wasn't smart and we started preserving them, they've just recovered really well. They'd be extinct (or at least near-extinct) if mankind as a whole all over the world made a concentrated effort to get rid of them, and it's slightly implied that this is exactly what the Anadlites do to their predators so even if andalite predators kept adapting to kill the Andalites eventually technology would have made it not only possible for the Andalites to wipe their predators out, the Andalite lifestyle would have made it necessary.
Any predator that evolved to continue preying on the Andalites would have been a danger since the Andalites don't live in cities or even very well defended homes, wolves don't pose that great a danger to a city full of people, and while a bear is the last thing you want to see knocking on your door they're not going to kill off entire towns. Similar predators could have wiped out entire andalite families since they live such secluded lives. Even a farmer in a wilderness of wolves has four walls and a roof to protect him, Andalites live in scoops which are just ditches in the ground with minor weather defense.
On the other hand think of what happens any time a predator kills a human being, we get up in arms to hunt it down and kill it so it doesn't happen again. When a lion eats a person an effort is made to kill that lion that often enough results in dozens of innocent lions dying as a result. Same for sharks, wolves, bears, chimps, any species that preys on us pays for it though sometimes the individual responsible isn't the one who pays. For the Andalites killing off all their predators or at least driving them into the places Andalites wouldn't bother going anyway, wouldn't have been anything less than a necessity for their safety unless they started building walls and such, which might have been less trouble but doesn't seem to fit the Andalite mentality.
To me at least this might imply why andalite warriors rarely ever morph in battle, we humans morph the things that kill us, maybe Andalites killed off all the things that killed them, this could also lend to their arrogance. Just imagine the things that would have hunted Andalites though, I mean look at Ankylosaur (sp's almost certainly off) a walking tank. Something forced it to evolve that way so's to avoid gettin' eaten, and then something evolved to get past that armor so's to keep eating it. So whatever evolved to outdo the andalite tail blade must have been one awesome beast.
