Literature that demonstrates organisms have a competitive advantage in numbers
I have found these papers:
http://www.sciencedirect.com/science/article/pii/S0169534713002322

http://www.sciencedirect.com/science/article/pii/S0040580912001360

http://www.ncbi.nlm.nih.gov/pubmed/19416834

http://www.ncbi.nlm.nih.gov/pubmed/21930936

The last two argue that larger groups have better "problem solving" capability, and this is a clear advantage in competition.