1. a Department of Geography and Resource Development , University of Ghana, Legon , P.O. Box LG59, Accra , Ghana E-mail:
2. b Department of Zoology , University of Ghana, Legon , P.O. box 67 LG, Accra , Ghana E-mail:
3. c Institute of Geography, University of Copenhagen , Oester Voldgade 10, DK 1350 , Copenhagen K E-mail: