These rapid climate changes were causing fundamental changes in the ecosystems of North America. Plants and animals were moving out of areas they had lived in and into new areas. Communities were coming apart and reorganizing. Many scientists think that these climatic and ecosystem changes caused the exinction at the end of the Pleistocene. The environmental changes might have caused extinction by eliminating food sources, disrupting birth schedules, or exposing animals to climatic conditions to which they were not adapted.