Biogeographic subdivisions of the earth

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Biogeographic subdivisionsof the earth
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Whither regions?

• 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?

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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 regionsthis concentration is called
  provincialism.
• Cosmopolitan species, genus of family that are
  widely distributed, throughout the world.

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

Endemic tree species In Central America

• For this reason, even the earliest biogeographers
  tended to try to recognize natural groupings of
  organisms in space. These various subdivisions
  have become known as (in descending order of
  size) realms or regions, subregions, provinces,
  and districts.

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• Good examples of provinces are the North American
  deserts
• Chihuahuan
• Sonoran
• Mojave
• Great Basin.

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

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Coefficients of Similarity

• Used to quantitatively compare floral and faunal
  similarities between regions.
• Jaccards Measure
• ____C_____
• 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
• Simpsons Measure
• C
• N1
• In both cases
• 1 harmony (flora fauna of both regions is
  identical)
• 0 no similarity between regions.

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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.

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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).

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Simpsons index of similarity
38
47
0
63-69
63-69
63-69
Mammal families in red. Flowering plant families
in blue.
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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.

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Philip Lutley Sclater (18291913)

• 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. Roughly, they are as
  follows

• Regio Palaearctica
• Regio Aethiopica
• III. Regio Indica
• IV. Regio Australiana
• V. Regio Nearctica
• VI. Regio Neotropica
• Sclater would later (1897) go on to publish a
  classification of biogeographic regions in the
  marine realm.

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Alfred Russel Wallace (18231913)

• 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)

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• Wallace greatly expanded upon Sclater's scheme of
  biogeographic regions. Wallace's system was
  based on vertebrates in general. He recognized
  sharp boundaries between these subdivisions,
  including a faunal break between Southeast Asia
  and Australiathis has become known as Wallace's
  Line. (see Map)
• Palearctic Region
• Ethiopian Region
• Oriental Region
• Australian Region
• Nearctic Region
• Neotropical Region

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World biogeographic regions
World faunal regions (zoogeography)
World floral regions (phytogeography)
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World biogeographic regions
World combined floral and fauna
regions (biogeography)
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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).

Isolines of mean wing length in Downy Woodpeckers
(Picoides pubescens)
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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).

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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).

Snowshoe Hare Throughout Canada and N. USA
Arctic Hare Northern Canada in tundra regions
Antelope Jackrabbit Arizona, New Mexico
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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)

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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.

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Patterns Minus Wanderers

• Australian - 91 Endemic-12 Families
• Neotropical - 47 Endemic-20 Families
• 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

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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.

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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.

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Wallaces line
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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.

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Holarctic region

• Holarctic is Palearctic plus Nearctic.
• Palearctic
• Europe, North Africa (to Sahara), Asia (except
  India, Pakistan and SE Asia) and Middle East.
• Number of vertebrate families 42
• Endemics families 0
• Nearctic
• Canada, USA, Mexico to tropics
• Number of families 37 endemics 2.

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Neotropic Ethipoian

• Neotropical
• tropical Mexico south to South America, plus the
  Antilles
• Number of families 50 endemics 19.
• Ethiopian
• Madagascar, Africa south of the
• Sahara, southern Arabian Peninsula
• Number of families 52 endemics 18.

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Oriental Australian

• Oriental
• Pakistan, India, Southeast Asia, Philippines,
  Indonesia west of Wallace's line (Sumatra, Java,
  Borneo)
• Number of families 50 endemics 4.
• Australian
• Australia, New Guinea, Tasmania,
• Indonesian Islands east of Wallace's line
• (Celebes, Timor, etc.)
• Number of families 28 endemics 17.

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• Communities, Formations
• and Biomes