1. Holechek , J.L. Cole , R.A. Fisher , J.T. Valdez , R.Natural Resources: Ecology, Economics, and Policy; Pearson Prentice Hall : Upper Saddle River, NJ , 2003 ; 716 – 718 .
2. Introduction: Balance and flux
3. Chiras , D.D. Reganold , J.P.Natural Resource Conservation: Management for a Sustainable Future; Pearson Prentice Hall : Upper Saddle River , 2005 ; 1 – 644 .
4. Knoll , A.Life on a Young Planet; Princeton University Press : Princeton , 2003 ; 1 – 296 .