[1] UNIV STOCKHOLM, DEPT METEOROL, S-10691 STOCKHOLM, SWEDEN
[2] UNIV MARYLAND, MARYLAND INT INST ECOL ECON, SOLOMONS, MD 20688 USA
[3] UNIV CAMBRIDGE, FAC ECON, CAMBRIDGE CB3 9DD, ENGLAND
[4] ROYAL SWEDISH ACAD SCI, BEIJER INT INST ECOL ECON, S-10405 STOCKHOLM, SWEDEN
[5] UNIV FLORIDA, DEPT ZOOL, GAINESVILLE, FL 32611 USA
[6] UNIV STOCKHOLM, DEPT SYST ECOL, S-10691 STOCKHOLM, SWEDEN
[7] PRINCETON UNIV, DEPT ECOL & EVOLUT BIOL, PRINCETON, NJ 08544 USA
[8] YORK UNIV, DEPT ENVIRONM ECON & ENVIRONM MANAGEMENT, YORK YO1 5DD, N YORKSHIRE, ENGLAND
[9] CORNELL UNIV, DEPT ENTOMOL, ITHACA, NY 14853 USA
[10] CORNELL UNIV, ECOL & SYSTEMAT SECT, ITHACA, NY 14853 USA