the zoogeographic concept has remained intact for well over a century. It was not
an attempt to micro-analyze the faunal world, but it provided a “big picture” of the
planet that would help aid the scientific classification of species so very much
debated in those times. In a sense, zoogeographic regions are the animal counter-
parts to plant-basedbiomes, but plants have secondary status in zoogeographic
regions. When zoogeographic regions are considered along with biomes and the
later-developed numeric climate classifications, there cannot help but be the sense
of the grand organization of the Earth by energy and moisture availability.
Wallace’s original map classifies oceanic islands as part of the six zoogeo-
graphic regions while not considering lifeinthe oceans. In a sense this was proper
because of the relative lack of knowledge about the oceans in the latter half of the
19th century. Later scholars have corrected this. A major addition to the concept
has been the inclusion of ocean life zones. These are usually identified as the same
zones used in describing the marine biomes of Earth.
Some studies have quantified boundaries via statistical analysis. Wallace’s clas-
sification as given here ignores extinct families and families that were unknown in
his day. Still, the zoogeographic concept was so strong that these names are still
used in the literature.
Table 6 is a listing of the number of animal families and the number of endemic
families of each zoogeographic region; an endemic species is one that has its
natural distribution solely in a single region. There are several versions of world
zoogeographic regions and they usually number six to nine. Here we use Wallace’s
original work.
The Neotropical Region is comprised of South America and tropical North
America. Animal families are diverse and this reflects the long separation of South
America from other regions and the variety of climates—fromdesertto tundra.
This is the region with the largest number of endemic families and is particularly
blessed with birds among the other vertebrate life.
The Nearctic Region is composed of non-tropical North America. The Nearctic
has had considerable amounts of species influx from the Palearctic Region because
of the land bridge between Siberia and Alaska in recent Earth history. The region
is usually viewed as transitional between the nearby Neotropical and Nearctic
regions. Although quite varied in climate, the Nearctic is not as diverse as its
neighbor regions.
The Palearctic is the largest zoogeographic region and encompasses northern
Eurasia and Africa north of the Sahara. The region is less diverse than those closer
to the equator because of limitations of warmth and/or moisture over large
expanses. Frequently, modern writers include the Nearctic and Palearctic as one
region known as the Holarctic in deference to the faunal impacts of the land bridge.374 Zoogeographic Regions