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CONSERVATON BIOLOGYLecture07 – Spring 2015 Althoff - reference Chapters 11-12
ISLAND BIOGEOGRAPHY
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Equilibrium Theories of Diversity
• Attempt to explain diversity patterns observed in natural ecosystem
• Some patterns noted:1) species richness increases dramatically from
high latitudes toward the equator2) within latitudinal belts, diversity appears to
be correlated with temperature, ecosystemproductivity, topographic heterogeneitywithin a region, and structural complexityof local habitats
3) ___________________ exhibit species impoverishment
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Equilibrium Theories of Diversity…con’t
• Everywhere, higher diversity is associated with greater ecological variety
• How do we explain these patterns of diversity?1) the ultimate source of diversity is __________
(the production of new species by the splitting of evolving lineages)
2) Species _________ (i.e., go extinct)—most species that have ever existed have disappeared
3) If Speciation Extinction….Species increase If Speciation Extinction….Species decrease4) Diversity might achieve a ________________
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Consider “steady-state” of species richness….
• Can examine this on a more localized level/scale (so do not think global scale for now)
• Best illustrated by examining patterns of diversity on oceanic islands
• Robert MacArthur and E.O. Wilson: EQUILIBRIUM THEORY OF ISLAND BIOGEOGRAPHY 1963 Evolution 17:373-387 (technical paper) 1967 Theory of Island Biogeography (book) ETIB
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• = the number of species on an island balances regional processes governing ____________ against local processes governing ______________.
Equilibrium Theory of Island Biogeography
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Number of species
Rat
e
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Number of species
Rat
eImmigration
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IMMIGRATION “Curve”
• As species fill an island, the ____________ of new species ______
Why? • As new species arrive, fewer are left on the
_________________• Those “left” on the mainland that haven’t
colonized have ___________________• Once all species from mainland have colonized,
immigration rate ____________
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Number of species
Rat
eImmigration
Extinction
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EXTINCTION “Curve”• As species fill UP the island, the ______ at
which they become _______________
Why?• Main reason: ______________________
______________ increases as species accumulate
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Other FACTORS to consider...• ____________________________
• ____________________________
• ____________________________• ____________________________
___________• ____________________________
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Who is most likely tocolonize?
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vs.
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Small vs. Large Islands
• Small islands support fewer species than larger islands…..
if _______________ from the mainland
Vs.
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vs.
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Near vs. Far Islands
• Islands near the mainland have more species than those farther away….
for ____________ islands
Vs.mainland
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___________________________ – in general…but same result over time
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ETIB
• Describes a ____________ and __________________________.
• Example, if a disaster exterminated part of an island’s biota, new colonists would—over time—restore diversity to pre-disturbance equilibrium
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Test of ETIB• Simberloff and Wilson (1970)• They first counted all arthropod species
present on each of 4 small mangrove islands in Florida Bay
• Then they removed entire arthropod fauna by fumigating the islands with methyl bromide
• Islands were resampled at regular intervals for a year
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Note ANote B
Note C
months
No
. o
f sp
ecie
s p
rese
nt
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Simberloff and Wilson study
• Note A: islands closer to sources of colonists recovered more species faster than more distant islands
• Note B: at the end of the year, species richness had leveled off, suggesting that an equilibrium had been reached
• Note C: the new equilibrium numbers of species were similar to the numbers of species before defaunation
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The Real World...
• True Islands• “Habitat” Islands
a) altitude barriersb) vegetation/habitat barriersc) disturbance
RESULT: __________________
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Relevance to Conservation Biology?
• Should guide our thinking about understanding how areas might be recolonized—or efforts that need to be made to “_________” recolonization (i.e., human transport, corridors, etc.)
• Should guide our thinking about ________ ________: big vs. small, one vs. many, near vs. far, etc.