Analysis of ecological systems : state-of-the-art in ecological modelling : proceedings of a symposium held from 24 to 28 May 1982 at Colorado State University, Fort Collins, Colorado, U.S.A. / edited by William K. Lauenroth, Gaylord V. Skogerboe, Marshall Flug ; sponsored by the International Society for Ecological Modelling (ISEM) ; hosted by the Natural Resource Ecology Laboratory, Colorado State University