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Class Biogeographic subdivisions Biogeographic endemic


Class Biogeographic subdivisions Biogeographic endemic

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									                                                                   BIOGEO 351 Winter 2005

              Class 17 - Biogeographic subdivisions of the earth
A central question in biogeography: Why are some groups of closely related plants or
animals found together in particular regions but are absent from other regions?

Endemism and provincialism
Endemism: a species, genus of family is restricted to one or a few geographic regions.

Organisms can be endemic to a location for two different reasons:
             • because they originated in that one place.
             • because they now survive in only a small part of their former range.

Endemic species tend to be concentrated in certain regions—this concentration is called

Cosmopolitan: species, genus of family that are widely distributed, throughout the

- endemic species do not occur randomly and they are not uniformly distributed, but
rather tend to be clumped.

Good examples of provinces are the North American deserts:
•Great Basin.

There are very few truly cosmopolitan species:
•Homo sapiens
•Rattus norvegicus

Coefficients of Similarity
Used to quantitatively compare floral and faunal similarities between regions.

Jaccard’s Measure
N1 + N2 - C

C = number of species, genera or families found in both regions
N1 = number of s/g/f in region 1
N2 = number of s/g/f in region 1

                                                                    BIOGEO 351 Winter 2005

Simpson’s Measure

In both cases:
1 = harmony (flora & fauna of both regions is identical)
0 = no similarity between regions.
Higher taxonomic levels = more cosmopolitan

Several reasons why higher taxonomic levels are more cosmopolitan:
•Individual species will occupy different niches but families of many species will occupy
a wide variety of habitats.
•Better dispersal ability overall with larger number of closely related species – range
expansion by species creates larger geographic range for the genus and family.
Higher taxonomic levels =
 more cosmopolitan
•Evolution works at the species level, so species can be narrow endemics but the family
will have many of these widely scattered species in many different niches.
•A species may go extinct but the family will survive (see point 3).
Biogeographical provincialism
The tendency for regions to possess unique species, genera or families.

Current biogeographic regions based on work done by Philip Sclater, who proposed that
the earth should be divided on the basis of similar taxon rather than geographic position,
environmental conditions or vegetation.

This approach is very different than that used for biogeographic biomes.

Philip Lutley Sclater (1829–1913)
A British ornithologist who discribed 1067 species and 135 genera of birds. In 1858 he
published an important paper in which he divided the world into biogeographic regions
on the basis of birds. This became the foundation for recognition of the six
biogeographic regions usually promoted today.

Alfred Russel Wallace (1823–1913)
British naturalist. The father of zoogeography who developed many of the basic concepts
and tenets of the field. He was also the co-discoverer of evolution by the means of
natural selection. Most of his contributions to biogeography are contained in 3 books:
        ―The Malay Archipelago‖ (1869)
        ―The Geographical Distribution of Animals‖ (1876)
        ―Island Life‖ (1880)

Wallace greatly expanded upon Sclater's scheme of biogeographic regions. Wallace's
system was based on vertebrates in general. He recognized sharp boundaries between

                                                                    BIOGEO 351 Winter 2005

these subdivisions, including a faunal break between Southeast Asia and Australia—this
has become known as Wallace's Line. (see Map)
        Palearctic Region
        Ethiopian Region
        Oriental Region
        Australian Region
        Nearctic Region
        Neotropical Region

Other biogeographic research at the time
        In the 19th century, one of the things that scientists began to do was to analyze
geographic variation in morphological characteristics. They came up with a number of
"rules of variation."

C. Bergmann (1847)—in endothermic vertebrates, races from cooler climates tend to
have larger body sizes, and hence smaller surface-to-volume ratios, than races of the
same species living in warmer climates (Bergmann's Rule).

Other biogeographic research at the time
C. L. Gloger (1833)—within a species, individuals from more humid habitats tend to be
darker in color than those from drier habitats (Gloger's Rule).

Other biogeographic research at the time
        J. A. Allen (1878)—among endothermic species, limbs and other extremities are
shorter and more compact in individuals living in colder climates (Allen's Rule).

Mammal taxa distribution
•90 common mammal families worldwide.
•11 families are relatively cosmopolitan and occur in all regions except Australia
(―wandering‖ mammals)
Soricidae (shrews)             Canidae (dogs)
Sciuridae (squirrels)          Felidae (cats)
Leporidae (rabbits)            Mustelidae (weasels)
Cervidae (deer)                Cricetidae (voles)
Ursidae (bears)

Mammal taxa distribution
•Non Neotropical and Australian – Bovidae (antelopes, cattle, gazelles, goats )
•Non Neotropical and Nearctic – Muridae (mice, rats).
•57% of 90 mammals families are endemic to only one region.
Patterns Minus ―Wanderers‖
Australian - 91% Endemic-12 Families
Neotropical - 47% Endemic-20 Families

                                                                    BIOGEO 351 Winter 2005

Ethiopian - 36% Endemic-14 Families
Oriental - 13% Endemic-4 Families
Nearctic - 13% Endemic-1 Family (region of Pleistocene extinctions and land bridges)
Palearctic - No Endemics

Biogeographic region hierarchy
 Biogeographic realms: several continents and large land masses
 Biogeographic regions: subdivide the earth     at the continental level.
 Biogeographic provinces: subdivision of the continents.

Biogeographic regional boundaries
Regions separated by oceans have well defined biogeographic boundaries; those in close
proximity do not.
Less distinct boundaries are more accurately termed biogeographic transition zones.

Species within transition zones have:
•different environmental requirements.
•different dispersal and colonization abilities.
•different long-term histories.
Wallace’s line

Biogeographic regions
Three important factors which lead to clearly definable faunal/floral regions:
•present location of biogeographic barriers.
•history of continental drift (plate tectonics)
•evolutionary history of modern plant and animal families.
Holarctic region
Holarctic is Palearctic plus Nearctic.

Europe, North Africa (to Sahara), Asia (except India, Pakistan and SE Asia) and Middle
Number of vertebrate families = 42
Endemics families = 0

Canada, USA, Mexico to tropics
Number of families = 37; endemics = 2.

Neotropic & Ethiopian
tropical Mexico south to South America, plus the Antilles
Number of families = 50; endemics = 19.

                                                                   BIOGEO 351 Winter 2005

Madagascar, Africa south of the Sahara, southern Arabian Peninsula
Number of families = 52; endemics = 18.

Oriental & Australian
Pakistan, India, Southeast Asia, Philippines, Indonesia west of Wallace's line (Sumatra,
Java, Borneo)
Number of families = 50; endemics = 4.

Australia, New Guinea, Tasmania, Indonesian Islands east of Wallace's line
(Celebes, Timor, etc.)
Number of families = 28; endemics = 17.


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