Animation Sequels

While watching Rio 2 in theatres today, I realized tha a lot of animated sequels follows a specific trope. Namely: the main character of the first movie is the last of something and eventually discovers that there's more of his kind in the sequel. That's exactly what happens in Rio 2. Blue thought he was the only blue macaw left, or rather one of the few remaining, and he finds a female, falls in love and has three children. Then, in the sequel, he meets his significant other's father and the rest of the "tribe," only he doesn't quite fit in at first and has to prove himself.
That's EXACTLY what happens in the Shrek series. Shrek is a lonely ogre who meets a princess who turns out to be another ogre. He meets her mother and father in Shrek 2, then has three children by the end of the movie who become part of the main plot in Shrek 3. In Shrek Forever After, he discovers more ogres, but doesn't quite fit in and has to prove himself.
Some of this applies to more movies too. In Kung-Fu Panda, Po thinks he's the last panda. By the end of Kung-Fu-Panda 2, we learn his father is still alive and there's a secret hidden tribe.
It goes on. In Madagascar, we have a set of domesticated wild animals who end up back in the wild. In Madagascar 2, Alex the lion is reunited with his family, and the rest of the animals discover more of their kind.