Picking some things out of the discussion to comment on
No. As kayak said, there are migrations of some mobs from one spot to another every season.
That's true, but that's not what I meant. I was talking about how a certain group of creatures used to be at that and that location in spring, and now since some time they're never at that location anymore in any season.
Otherwise, mobs spawn in a given area by groups.
That's usually true, but not always. Most mobs spawn by groups, where the entire group respawns only once the last creature in it is dead and decayed. But there are some groups in which the creatures respawn individually. These groups can be a real pain because it's impossible to prevent their respawn by leaving only one of them alive.
Also there, you'll see that there are different types of predator/prey couples. All carnivores don't eat the same herbivores.
As far as I can tell, a carnivore will attack any herbivore that's slower than it. If the carnivore can't catch the herbivore, it doesn't even bother trying to.
Mektoubs are the fasters creatures on Atys, so no predator tries to hunt them. That's why mektoubs are often found grazing peacefully amongst predators. (If homins didn't tame so many mektoubs into mounts and packers only to get them killed, mektoubs would probably overpopulate Atys

)
Torbaks won't hunt gnoofs because gnoof are faster than torbak. Cuttlers though are faster than gnoofs and will hunt them.
Jugulas are really slow and don't hunt much of anything. Only yelks are on their menu, I believe. That must be how they get their poison breath
I noticed this changed after the patch that changed some of the less than challenging herbivore's where made harder to kill.
Oh, I had forgotten about that. It's indeed quite likely that's the cause.
one may prospect, but sources behind you only really "pop" (if you are alone) when you turn around.
Heh, it's the same with sources that you prospect outside your sight range. They don't pop until you get closer.