Accumulated knowledge about nature is an important part of people's capacityto manage and conserve the environment. But this ecological knowledge is now being increasingly lost. There have been few cross-cultural and quantitative studies to describe the phenomenon of its loss. Here we show a strong inverse correlation between ecological knowledge and income levels in and among India, Indonesia, and the U.K. (n=1095 interviews). Knowledge acquisition and subsequent saturation occurs at an early age in the most resource-dependent communities, but not in the U.K., where knowledge levels are low and acquisition is slow. Knowledge variance within communities increases in association with ecological knowledge decline and a scale of progressive knowledge loss was revealed with the most rapid rates of loss in industrialized regions. Various studies have described the mutually exclusive relationship between economic growth and environmental conservation; however this is the first to consider the association between economic growth and social capacity to manage the environment. Understanding ecological knowledge loss is importantto understanding the declining capacities of communities undergoing economic development to manage their natural resources and the future of ecosystem diversity in the light of current patterns of economic growth.