@article{56930,
      author = {Levins, Richard.},
      url = {http://library.usi.edu/record/56930},
      title = {Evolution in changing environments; some theoretical  explorations.},
      publisher = {Princeton University Press,},
      recid = {56930},
      pages = {ix, 120 p.},
      address = {Princeton, N.J.,},
      year = {1968},
}