Jack is the junior, Ace the senior. As you see, senior is not always happy to have Jack's attention.
No Shepherds were hurt in the making of this image :D
As you see, they often can collaborate very well, such as in this image, where they are both comfortably ensconced on my couch, which is supposed to be DOG FREE!
I love that couch picture too - they look like they've just had a spat but can't leave so they are doing their best to pretend the other isn't there!! Ha! Beautiful shepherds - my favorite breed.