1. Department of Animal Ecology, Ecology Building, Lund University, Sölvegatan 37, S-223 62 Lund, Sweden
2. Division of Structural Mechanics, Lund Technical University, John Ericssons Väg 1, S-223 63 Lund, Sweden
3. Department of Theoretical Ecology, Ecology Building, Lund University, Sölvegatan 37, S-223 62 Lund, Sweden