There was a show recently on Nature on the PBS network about how many differerent species thrived by evolving the ability to work cooperatively. I will try to find a link to that show. It is to the advantage of many animals to work this way.
Here it is:
http://www.pbs.org/wnet/nature/trium.../episode4.html
Life may be a contest in which only the fittest individuals survive, but cooperation has also played a key role in evolution. WINNING TEAMS takes a close look at the alliances that animals have forged -- with others of their own kind and very different organisms -- in a bid to stay alive. In fact, teamwork occurs everywhere, from flocks of birds and herds of wildebeest to colonies of ants and termites.