1. Department of Ecology, Evolution, and Environmental Biology, Columbia University,New York, New York 10027 USA
2. Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama
3. Centre for Ecology and Hydrology; Bush Estate, Penicuik Midlothian, Scotland EH26 0QB United Kingdom
4. Department of Environmental Science, University of Puerto Rico, Box 70377, Rio Piedras, San Juan 00936-8377 Puerto Rico