For the thoroughbred racehorse see Nearctic (horse).
The World Wide Fund for Nature (WWF) divides the Nearctic into four Bioregions, defined as "geographic clusters of ecoregions that may span several habitat types, but have strong biogeographic affinities, particularly at taxonomic levels higher than the species level (genus, family)."
- Flannery, Tim 2001. The eternal frontier: an ecological history of North America and its peoples. Grove Press, New York.
- Ricketts, Taylor H., Eric Dinerstein, David M. Olson, Colby J. Loucks et al. 1999. Terrestrial ecoregions of North America: a conservation assessment. Island Press, Washington DC.