Animals do not have the same mental abilities as humans, but if you think logically about nature animals have to be able to learn and remember. If a hunting party of wolves discovers a meadow that is full of deer it would be in their best interest to come back there next time they’re hunting. Also when most pack animals hunt, some go hunting and some stay home. If a wolf wasn’t able to remember every time someone went hunting the wolves left at home would assume they were gone forever and wander off to make their own way in the world.
If an animal wasn’t able to understand that something still exists even when it’s "gone away" they would starve to death. If a lion is hunting and an antelope runs over a rise and disappears behind a hill the lion doesn’t think the antelope is gone, she knows it’s just out of sight and continues hunting it.
Also try to recall a time when you accidently left something delicious out on a table and your dog got to it. Chances are good that the next few times he went into that room he went right back to that table to make sure you didn’t leave another turkey sandwich there. Remembering is critical to an animal’s survival. Dogs with seperation anxiety will be worried when you leave that you’re never coming back, but a dog that is secure knows that when you leave the house you’ll be back sooner or later.

I have one "mama’s girl" who hubby refuses to be left alone with because she hunts me. Not actualy separation anxiety but she literally goes everywhere with me. If I leave she will wait under carport at gate until my return. She also knows when I take particular plates out that means they get to eat and she goes crazy. One gets shots and when the alarm on my cell goes off at 9 a.m and 9 p.m. he automatically goes to the fridge. If the water bowl is empty, he goes to the tub or the sink and taps at it with his paw and sometimes barks. He knows that’s where the water comes from. Never at the toilet though! I can pick up scissors or clippers and they all leave the room! One waits at the side of the couch and grunts and when my husband moves his arm away from his side about 3 inches, he hops up there to lay down. He always asks for permission first. He will stand and bark at the cabinet where the treats are. Mine don’t seem to have sense of time about when we leave though. I have to travel overnight a lot and might be gone 15 hours at the most. One of them fusses with a particular high pitched bark constantly for a few minutes when we return. Where were, why didn’t you take us, I’m mad, you left us alone. Yet sometimes I can run to the store and back, gone maybe 5 minutes and they act like it’s been 2 days. Just always lots of unconditional love. I ALWAYS have to pick each of them up individually and love on them when I get home or they will not leave me alone.