1. ^ Honey, Martha (2008). Ecotourism and Sustainable Development: Who Owns Paradise? (Second ed.). Washington, DC: Island Press. pp. 33. ISBN 1597261254 ISBN 978-1597261258.

  2. ^ Untamed Path | Defining Ecotourism. Retrieved on 2009-03-24.


  3. ^ a b Randall, A. (1987). Resource economics, Second Edition. New York, USA: John Wiley and Sons.