What does co mean in coevolution?

Co-evolution refers to a process by which 2 or more individual species evolve in a manner that acknowldeges the presence of the other. This is commonly seen in symbiotic relationships, whereby both organisms bennefit from a certain relationship. Further "co-evolution" of this relationship may result in traits in one of the species that necessitates the existence of the other.

However, this process can also be seen with two opposing species that share the same environment. This is most often manifest as an "arms-race" between predator and prey. For example, the early gazelle developed speed to get away from the early lion... then the lion caught up by developing stronger claws, or group tactics (this may not be the exact evolutionary history, but it serves the point). Indeed in some rather confined ecosystems, where predator-prey exist with only 2 involved species, there can be some extreme forms of arms races, perpetuated by the fact that the prey only has to adapt to one predator and vice-versa.

For example, garter snakes have co-evolved with the toxic newt Taricha granulosa in the pacific NW. As the newt developed a more toxic secretion, via natural selection, the snake developed greater resistance. At the current point in the arms race, the snake can eat the newt, but it must remain sedentary until the poison is broken down.

Hope this helps

George