?url_ver=Z39.88-2004&rft_id=10.1086%2F285875&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.au=Ferriere%2C+R.&rft.aulast=Ferriere&rft.aufirst=R.&rft.issue=5&rft.volume=147&rft.date=May+1996&rft.issn=0003-0147&rft.atitle=The+evolution+of+cooperation+in+spatially+heterogeneous+populations&rft.title=The+American+Naturalist&rft.pages=692-717&rft.genre=article