Transcript Island biogeography

Ch. 9—Key concepts & terms
• Biogeography concepts
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Biome / faunal realm
Dispersal routes and barriers
Centers of dispersal
Latitudinal diversity gradient
Island biogeography
• Paleobiogeography and plate tectonics
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Pangaea
Viking funeral ships / Noah’s Ark
Accreted terranes
Mammalian paleobiogeography
Fossils & Evolution—Chapter 9
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Chapter 9—Biogeography
• 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
Fossils & Evolution—Chapter 9
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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
Fossils & Evolution—Chapter 9
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North American biomes
tundra
coniferous
forest
rain
forest
temperate
deciduous
forest
cold desert
hot desert
temperate
Fossils & Evolution—Chapter 9 grassland
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Terrestrial faunal realms
Fossils & Evolution—Chapter 9
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Paleobiogeography
• Paleobiogeography is concerned with
determining the geographic ranges of
extinct taxa and geographic expansion
from evolutionary centers of origin
Fossils & Evolution—Chapter 9
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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
Fossils & Evolution—Chapter 9
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Bering Land Bridge
(Paleogene through Wisconsin glacial stage)
Fossils & Evolution—Chapter 9
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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)
Fossils & Evolution—Chapter 9
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Fossils & Evolution—Chapter 9
Miocene (20 Ma)
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Isthmus of
Panama
(~3.2 Ma)
Fossils & Evolution—Chapter 9
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Barriers and provincialism
• Paleozoic foram example
Fossils & Evolution—Chapter 9
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Mississippian forams
14%
New World
endemics
Old World
endemics
20%
cosmopolitan
66%
Rheic Ocean
(marine corridor)
Fossils & Evolution—Chapter 9
source: Ron Blakey: http://www4.nau.edu/geology/
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11%
Pennsylvanian forams
New
World
endemics
24%
cosmopolitan
Old World
endemics
65%
Fossils & Evolution—Chapter 9
source: Ron Blakey: http://www4.nau.edu/geology/
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Fossils & Evolution—Chapter 9
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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
Fossils & Evolution—Chapter 9
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Generic diversity of hermatypic
corals
centers of
dispersal9
Fossils & Evolution—Chapter
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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)
Fossils & Evolution—Chapter 9
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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
Fossils & Evolution—Chapter 9
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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
Fossils & Evolution—Chapter 9
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Species diversity vs. island area
Fossils & Evolution—Chapter 9
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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
Fossils & Evolution—Chapter 9
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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
Fossils & Evolution—Chapter 9
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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
Fossils & Evolution—Chapter 9
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Paleoiogeography (cont.)
• Wegener and other early proponents of
continental drift cited fossil evidence for
the existence of a Late Paleozoic–Early
Mesozoic supercontinent (Pangaea)
• Such evidence was largely discounted
(even by G. G. Simpson) until 1960s when
overwhelming geophysical evidence
“proved” sea-floor spreading
Fossils & Evolution—Chapter 9
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Fossil evidence for fusion of southern
continents (Gondwanaland)
Fossils & Evolution—Chapter 9
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Lystrosaurus
Fossils & Evolution—Chapter 9
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Modes of dispersal
• Recall Simpson’s 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
– Noah’s Ark = living organisms rafted to a new
land mass aboard a microcontinent or island arc
Fossils & Evolution—Chapter 9
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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
Fossils & Evolution—Chapter 9
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Continental
accretion
Fossils & Evolution—Chapter 9
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icrocontinents
th Permian fossils
Asian affinity
Jurassic
Fossils & Evolution—Chapter 9
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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
Fossils & Evolution—Chapter 9
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rifting of
Australia from
Antarctica
Eocene (~50 Ma)
Fossils & Evolution—Chapter 9
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Noah’s
Ark?
Isolated
faunal realm
Fossils & Evolution—Chapter 9
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Geographic
phylogeny of
marsupials
Fossils & Evolution—Chapter 9
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