Nearctic realm

Definition

One of the eight terrestrial biogeographic realms, encompassing North America north of tropical Mexico, Greenland, and the Canadian Arctic Archipelago. The Nearctic is characterized by temperate and boreal ecosystems, with distinctive endemic insect lineages such as certain tiger beetles (Cicindelidae) and diving beetles (Dytiscidae) that diversified during Pleistocene glaciation cycles. It shares a long evolutionary history with the Palearctic realm, with which it was periodically connected via Beringia, resulting in substantial faunal exchange and shared Holarctic distributions for many arthropod groups.

Etymology

From Greek neos (new) + arktos (north), coined by Philip Lutley Sclater in 1858 to distinguish the New World north from the Palearctic (Old World north).

Example

The tiger beetle genus Cicindela shows classic Nearctic endemism, with species such as C. patruela restricted to eastern deciduous forests, while other lineages like C. oregona demonstrate trans-Beringian connections to Palearctic relatives.

Synonyms

• Nearctic region
• Nearctic ecozone

Related Terms

• Palearctic realm
• Holarctic
• Neotropical realm
• biogeographic realm
• Beringia
• Endemic

Usage Notes

Capitalized as a proper noun referring to the specific biogeographic unit. Contrasts with Neotropical realm to the south; together with Palearctic, forms the Holarctic. In entomological literature, 'Nearctic' often appears as an adjective (e.g., 'Nearctic fauna'). The boundary with the Neotropical realm runs through central Mexico and southern Florida, creating a transition zone with mixed faunal elements.