This chapter explores the definition of "nature" by providing a review of the long-term alteration of natural ecosystems by humans in the context of specific examples from pre-Columbian Latin America, with special emphasis on lowland South America and Costa Rica. Archaeological evidence suggests that humans have been a keystone species in most natural habitats in the Americas since the end of the Pleistocene. This chapter argues that indigenous peoples of Latin America have played an essential role in shaping landscapes and ecosystems, both consciously and unconsciously, through the use of fire as well as a range of innovative agricultural technologies. It uses specific examples from pre-Columbian Latin America to explain how studies of archaeology, ethnohistory, and iconography have been useful in documenting the contributions of native populations to habitat alteration, how it has been experienced by these populations, and how it is interpreted by scholars.