Ch. 9

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Ch. 9Key concepts terms

• Biogeography concepts
• Biome / faunal realm
• Dispersal routes and barriers
• Centers of dispersal
• Latitudinal diversity gradient
• Island biogeography
• Paleobiogeography and plate tectonics
• Pangaea
• Viking funeral ships / Noahs Ark
• Accreted terranes
• Mammalian paleobiogeography

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Chapter 9Biogeography

• Biogeography is the study of the geographic
  distribution of plants and animals (on a scale
  larger than that of ecologic analysis)
• Biogeography is intimately linked with geology
  because the modern distribution of organisms has
  arisen over millions of years, in response to
  changes in climate and geography
• Paleobiogeography is concerned with determining
  the geographic ranges of extinct taxa and
  geographic expansion from evolutionary centers of
  origin

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Biomes

• Biome a broadly homogeneous association of
  plants and animals that occurs over a large area
  of land
• Governed by climate
• A given biome cannot occur in widely separated
  land areas (e.g., different continents) because
  of barriers to dispersal
• Faunal realms usually correspond with portions of
  continents or even groups of continents

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North American biomes
tundra
coniferous forest
rain forest
temperate deciduous forest
cold desert hot desert
temperate grassland
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Terrestrial faunal realms
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Paleobiogeography

• Paleobiogeography is concerned with determining
  the geographic ranges of extinct taxa and
  geographic expansion from evolutionary centers of
  origin

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Dispersal routes and barriers

• Biogeographic routes and barriers vary in the
  degree to which they limit migration (virtually
  no barrier is absolute)
• Corridors unobstructed migration routes (e.g.,
  Bering land bridge during Tertiary)
• Sweepstakes routes dispersal routes that are
  crossed rarely and only by chance (e.g.,
  terrestrial vertebrate rafted across narrow
  ocean)
• Filters intermediate between corridor and
  sweepstakes (sometimes one-way only)
• Plate tectonics can cause changes in the nature
  of barriers

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Bering Land Bridge(Paleogene through Wisconsin
glacial stage)
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Sweepstakes to Corridor transition(or corridor
to sweepstakes?)

• Isthmus of Panama
• No isthmus existed for most of Cenozoic time
• South American mammal fauna was endemic with only
  a few immigrants via sweepstakes routes (e.g.,
  monkeys from Old World)
• North American mammal fauna enjoyed free
  interchange with NE Asia
• Isthmus of Panama was emplaced in Pliocene (3 to
  3.5 Ma), establishing a land corridor for
  interchange (and marine barrier between Atlantic
  and Pacific)
• North American predators largely out-competed
  South American ones South American marsupials
  invaded North America (opossum)

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Miocene (20 Ma)
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Isthmus of Panama(3.2 Ma)
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Barriers and provincialism

• Paleozoic foram example

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Mississippian forams
Rheic Ocean (marine corridor)
source Ron Blakey http//www4.nau.edu/geology/
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Pennsylvanian forams
source Ron Blakey http//www4.nau.edu/geology/
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Centers of dispersal

• Idea that major taxa originate and undergo
  initial diversification in particular regions
• Diversity of species declines away from center of
  dispersal
• Tropical and subtropical regions seemingly have
  been centers of dispersal throughout much of the
  Phanerozoic
• e.g., dispersal of hermatypic reef corals

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Generic diversity of hermatypic corals
centers of dispersal
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Latitudinal diversity gradient

• Tropics contain greatest number of species, with
  diversity declining in higher latitudes
• Dt Dt-1 No Ne, where No number of
  originations and Ne number of extinctions
• So, is No greater in the tropics? Is Ne lower in
  the tropics? No lower in the high latitudes? Ne
  higher in the high latitudes?
• Answer higher Ne in high latitudes (at least for
  birds and mammals)

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Island biogeography

• Island biogeography is an important concept
  because there are lots of isolated habitats (real
  and virtual islands)
• Lakes are islands surrounded by a sea of land
• Mountain tops are islands surrounded by a sea of
  lower elevation
• Patch reefs are islands surrounded by a sea of
  level bottom seafloor

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Island biogeography

• Species diversity increases as area of island
  increases
• S cAz,
  
• where S diversity c constant A area z
  constant ranging from 0.20 to 0.35

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Species diversity vs. island area
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Island biogeography

• Why does species diversity increase with
  increasing area?
• Probability of immigration is higher on larger
  islands
• Less crowding on larger islands
• Greater variety of habitats on larger islands

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Island biogeography

• Relict faunas faunas whose geographic range is
  but a remnant of a previously much larger range
• e.g., Cold-adapted species that today are
  stranded on mountain tops
• In Pleistocene ice age they were widespread
• As climate warmed, species with poor dispersal
  mechanisms were left stranded in cold climates on
  mountain tops

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Paleobiogeography

• Modern day distribution of plants and animals is
  governed largely by climate and continental
  configurations
• Distribution of fossil taxa on modern continents
  does not make sense except in light of
  continental drift and accreted terranes

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Paleoiogeography (cont.)

• Wegener and other early proponents of continental
  drift cited fossil evidence for the existence of
  a Late PaleozoicEarly Mesozoic supercontinent
  (Pangaea)
• Such evidence was largely discounted (even by G.
  G. Simpson) until 1960s when overwhelming
  geophysical evidence proved sea-floor spreading

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Fossil evidence for fusion of southern continents
(Gondwanaland)
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Lystrosaurus
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Modes of dispersal

• Recall Simpsons modes of dispersal
• Corridors, filters, sweepstakes routes
• With acceptance of plate tectonics, two
  additional modes are now recognized
• Viking funeral ship fossils rafted to a new
  land mass aboard a microcontinent or island arc
• Noahs Ark living organisms rafted to a new
  land mass aboard a microcontinent or island arc

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Viking funeral ship

• Example Late Paleozoic accreted terranes of
  western North America
• Permian fusulinid faunal provinces were
  recognized in 1960s, but their distribution on
  modern continents was difficult to explain prior
  to acceptance of plate tectonics
• Now, exotic crustal belts in western North
  America are interpreted as accreted terranes
• Permian sedimentary rocks and oceanic crust that
  were accreted to North America during early
  Mesozoic

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Continentalaccretion
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microcontinents with Permian fossils of Asian
affinity
Jurassic
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western accreted terranes
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Permian paleogeography
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Plate tectonics and isolation of Australian
marsupials

• Plate tectonic isolation has allowed certain
  primitive animals to survive on Australia
• Marsupials originated in North America
• Migrated to South America in late Cretaceous
• Then to Australia via Antarctica by Oligocene
  time
• Convergent evolution between placental and
  marsupial mammals
• Similar forms among animals adapted for similar
  life styles

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rifting of Australia from Antarctica
Eocene (50 Ma)
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NoahsArk?Isolatedfaunal realm
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Geographicphylogeny ofmarsupials