Jie Li is Professor at Institute for Population and Development Studies, School of Public Policy and Administration, Xi'an Jiaotong University, China. Shuzhuo Li is Professor at Institute for Population and Development Studies, School of Public Policy and Administration, Xi'an Jiaotong University, China. Gretchen C. Daily is Bing Professor in Environmental Science, Department of Biology, Stanford University, USA. Marcus Feldman is Professor of Biological Sciences and director, Morrison Institute for Population and Resource Studies, Stanford University, USA.