Holarctic Realm

Definition

One of the six major biogeographic realms, encompassing the temperate, boreal, and Arctic regions of the entire Northern Hemisphere. The Holarctic comprises the Nearctic (North America and Greenland) and Palearctic (Eurasia and North Africa) regions, united by Pleistocene land connections and sharing many plant and animal lineages that dispersed across Beringia and the North Atlantic land bridges. In entomology, the realm is notable for extensive circumpolar distributions of cold-adapted insects and the presence of numerous trans-Beringian sister species pairs.

Etymology

From Greek holos (whole, entire) + arktikos (of the Bear, northern), modeled on 'Palearctic' and 'Nearctic' by biogeographers in the early 20th century to recognize the fundamental unity of northern temperate and Arctic biotas.

Example

The mourning cloak butterfly (Nymphalis antiopa) exhibits a classic Holarctic distribution, with closely related populations occurring across North America, Europe, and temperate Asia—a pattern reflecting post-glacial range expansion from shared Pleistocene refugia.

Synonyms

• Holarctic region
• Holarctic

Related Terms

• Nearctic
• Palearctic
• Beringia
• biogeographic realm
• circumpolar distribution
• Pleistocene refugium
• Siberian-Manchurian disjunction

Usage Notes

Used both as a formal biogeographic designation (capitalized) and as a descriptive adjective (often lowercase: 'holarctic species'). Specialists distinguish the Holarctic as a realm from its constituent Nearctic and Palearctic regions; the term should not be applied to southern hemisphere taxa. 'Holarctic' distribution patterns are frequently contrasted with 'Holarctic-African' or 'Holarctic-Oriental' disjunctions in insect phylogeography. Some authors restrict 'Holarctic' to the combined Nearctic-Palearctic zone north of the tropics, excluding North African and Middle Eastern steppe zones.