In the never-ending challenge to survive and reproduce, living things must evolve in response to their physical environment, as well as to their fellow organisms. Under the right conditions, these pressures cause new species to arise and local biodiversity to increase. Such conditions have made the Great Barrier Reef one of the most diverse ecosystems in the world.
Inside this complex system, every organism interacts with enemies, competitors, and partners. Over scores of generations, these relationships are honed into near-perfect operations. Predators seem perfectly adapted to catching their prey, competitors know all the right moves to get their mate, and partners can't live without each other.
But this near-perfection is a mirage. The relationships are really a constant tug-of-war among organisms. When one evolves a new feature or behavior, it pulls on all of its relationships. If the other organisms can't pull back with evolutionary changes of their own, the relationship will fall apart. And so the evolutionary game continues.