Both the symbiotic and the predator/prey relationships evolve together. For the symbiotic take the example of the bird on the rhino's back. They are both in the same environment so their relationship evolves (develops) together, helping each other out. The bird gets to eat the bugs on the rhino and the rhino is kept for being infested with bugs. In the predator/prey situation, think about the lion and antelope. The lion is the predator looking for food. The prey is what he eats. Only the fastest and most able-bodied lions are going to get the antelope. In order for the antelope to survive, it must become swifter and better able to conceal itself. The best of both animals will survive thus strengthening their blood lines. The difference between how the pairs evolve is their interaction. Symbiotic help each other; they don't do harm to one another. Predator/prey relationships is the opposite. The lion intends to do harm to the antelope. He needs the antelope for food.
