Post on 03-Feb-2016
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Island biogeography I: the idea
Bio 415/615
Questions
1. What are the opposing forces of island biogeography?
2. Why do islands have fewer species than continental areas of the same size?
3. How has IBT been tested?4. What is the rescue effect?
Habitat diversity
Habitat diversity
Population size
Population size
Bigger ranges
Bigger ranges
Recall species-area relationships
Log AreaLog Area
Log
Sp
ecie
s
Log
Sp
ecie
s
Ric
hn
ess
Ric
hn
ess
Consider islands
• Bigger islands should have more species than smaller islands. Why?– More habitats (or env circumstances)– Support larger populations– Can hold larger animals (e.g., big
ranges)
• What else determines how many species are on islands?
Richness as a f(area, distance)Richness as a f(area, distance)
Island Observations
Islands have fewer species than samples within contiguous
continental areas as a function of size
Islands have ever fewer species as they get smaller (z is higher)
Isolated islands have fewer species than less isolated islands
of the same size
Beyond Islands: Habitat Loss & Beyond Islands: Habitat Loss & FragmentationFragmentation
• Area decreases (Grain Area decreases (Grain decreases)decreases)
• Isolation increases (Distance Isolation increases (Distance increases)increases)
• Fewer species expectedFewer species expected• InsularizationInsularization
Occam’s principle of Occam’s principle of parsimony with a warning parsimony with a warning
from Einsteinfrom EinsteinOne should not One should not
increase beyond increase beyond what is necessary what is necessary the number of the number of entities required to entities required to explain anythingexplain anything
William of OckhamWilliam of Ockham
Everything should be Everything should be made as simple as made as simple as possible but not possible but not simplersimpler
Albert EinsteinAlbert Einstein
IBTIBT
The TheoryThe Theory
• Immigration, extinctionImmigration, extinction– Straight to concaveStraight to concave
• TurnoverTurnover• Near, FarNear, Far• Large, SmallLarge, Small
Immigration RateImmigration RateR
ate
of
New
Sp
ecie
s
Imm
igra
tion
Number of Resident Species0 ManyLow
High
Extinction RateExtinction Rate
Rate
of
Exti
ncti
on
Number of Resident Species0 ManyLow
High
Rate
of
New
Sp
ecie
s
Imm
igra
tion
EquilibriumEquilibrium
Number of Resident Species0 ManyLow
High
Equilibrium
Rate
of
New
Sp
ecie
s
Imm
igra
tion
Rate
of
Exti
ncti
on
Turnover
IsolationIsolation
Number of Species
Far from Mainland
Rate
of
Exti
ncti
on
Rate
of
New
Sp
ecie
s
Imm
igra
tion
AreaArea
Number of Species
Large Island
Rate
of
Exti
ncti
on
Rate
of
New
Sp
ecie
s
Imm
igra
tion
EquilibriumEquilibrium
Number of Species
Small, Far Island
Rate
of
Exti
ncti
on
Rate
of
New
Sp
ecie
s
Imm
igra
tion
EquilibriumEquilibrium
Number of Species
Small, Close Island
Rate
of
Exti
ncti
on
Rate
of
New
Sp
ecie
s
Imm
igra
tion
EquilibriumEquilibrium
Number of Species
Large, Close Island
Rate
of
Exti
ncti
on
Rate
of
New
Sp
ecie
s
Imm
igra
tion
EquilibriumEquilibrium
Number of Species
Large, Far Island
Rate
of
Exti
ncti
on
Rate
of
New
Sp
ecie
s
Imm
igra
tion
IBTIBT
Extensions of TheoryExtensions of Theory
• Target effectTarget effect• Rescue effectRescue effect
II EE
DistanceDistance MWMW RescueRescue
AreaArea TargetTarget MWMW
Rescue effectRescue effect
Brown & Kodric-Brown 1977
Isolation influences extinction rates of extant species too, by ‘rescuing’ them from extinction through continuous supply of more individuals
Area and IsolationArea and Isolation
Number of Species
RescueEffect
TargetEffect
Rate
of
Exti
ncti
on
Rate
of
New
Sp
ecie
s
Imm
igra
tion
Bigger islands are bigger ‘targets’ for colonization
Extensions of TheoryExtensions of Theory
• Target effectTarget effect• Rescue effectRescue effect• Landscape ecology: matrix, Landscape ecology: matrix,
patch quality, corridorpatch quality, corridor
Simberloff: Experimental TestSimberloff: Experimental Test
Simberloff’s mangrove Simberloff’s mangrove islandsislands
Land bridge islandsLand bridge islandsBarro Colorado Island, PanamaBarro Colorado Island, Panama
1. Hilltop = 15.7 km2 of lowland tropical 1. Hilltop = 15.7 km2 of lowland tropical forest.forest.
2. Isolated in 1914 when Lake Gatun was 2. Isolated in 1914 when Lake Gatun was formed by construction of the Panama formed by construction of the Panama Canal.Canal.
3. Knowing area and period of isolation, 3. Knowing area and period of isolation, can model extinction. can model extinction.
4. 108 species of breeding birds in 1938.4. 108 species of breeding birds in 1938.
5. Terborgh used land bridge model to 5. Terborgh used land bridge model to predict 17 would be lost in 50 years; really predict 17 would be lost in 50 years; really 13 = 12% of 108.13 = 12% of 108.
So why does insularizationSo why does insularizationlead to species loss?lead to species loss?
The 3 Step Process of Species Loss and The 3 Step Process of Species Loss and Extinction DebtExtinction Debt
The 3 Step Process of Species Loss and The 3 Step Process of Species Loss and Extinction DebtExtinction Debt
InstantaneousInstantaneous
FastFast
SlowSlow
SamplingSampling
IsolationIsolation
AreaArea
The 3 Step Process of Species Loss and The 3 Step Process of Species Loss and Extinction DebtExtinction Debt
InstantaneousInstantaneous
FastFast Faster & Faster & GreaterGreater
Loss as AreaLoss as Area
SlowSlow
The 3 Step Process of Species Loss and The 3 Step Process of Species Loss and Extinction DebtExtinction Debt
InstantaneousInstantaneous
FastFast Faster & Faster & GreaterGreater
Loss as AreaLoss as Area
SlowSlow
The 3 Step Process of Species Loss and The 3 Step Process of Species Loss and Extinction DebtExtinction Debt
InstantaneousInstantaneous
FastFast Faster & Faster & GreaterGreater
Loss as AreaLoss as Area
SlowSlowExtinction debt Extinction debt Steeper zSteeper z
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