Species, Area,
& the Equilibrium Theory of
Island Biogeography
as a foundation paradigm
in conservation biology
Species, Area,
& the Equilibrium Theory of
Island Biogeography
as a foundation paradigm
in conservation biology
Conservation planning & design
Fragmentation effects
Species loss equation—predicting extinction
Island models in gene flow, metapopulations,
landscape ecology
• Samples, within contiguous area
• Isolates, islands, z high
• Samples, within contiguous area, z low
• Isolates, islands
The Plot Thickens!
Richness as a f(area, distance)
% Saturation as a f
(distance)
Species-area relations
•
•
•
•
•
S = cAz
z is much less than 1
log S = log c + z log A
Variation in c: places and taxa
Variation in z: area and isolation
z = .10-.15 for samples
z = .18-.35 for islands
IF z = .3, 50/10 Rule
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
Threat 1: Habitat Loss
& Fragmentation
• Area decreases (Grain decreases)
• Isolation increases (Distance
increases)
• Fewer species expected
• Insularization
Occam’s principle of parsimony
with a warning from Einstein
One should not increase
beyond what is
necessary the number
of entities required to
explain anything
William of Ockham
Everything should be
made as simple as
possible but not
simpler
Albert Einstein
IBT
The Theory!
• Immigration, extinction
– Straight to concave
• Turnover
• Near, Far
• Large, Small
Immigration Rate
Rate of Immigration
High
Low
0
Number of Species
Many
Extinction Rate
Rate of Extinction
High
Low
0
Number of Species
Many
Equilibrium
Low
Rate of Extinction
Rate of Immigration
High
Equilibrium
0
Number of Species
Many
Far from Mainland
Number of Species
Rate of Extinction
Rate of Immigration
Isolation
Rate of Immigration
Large Island
Number of Species
Rate of Extinction
Area
Small, Far Island
Number of Species
Rate of Extinction
Rate of Immigration
Equilibrium
Small, Close Island
Number of Species
Rate of Extinction
Rate of Immigration
Equilibrium
Large, Close Island
Number of Species
Rate of Extinction
Rate of Immigration
Equilibrium
Large, Far Island
Number of Species
Rate of Extinction
Rate of Immigration
Equilibrium
IBT
Extensions of Theory!
• Target effect
• Rescue effect
I
E
Distance
MW
Rescue
Area
Target
MW
Extensions of Theory!
• Target effect
• Rescue effect
• Landscape ecology: matrix, patch
quality, corridor
Simberloff: Experimental Test
Another kind of evidence…
• Species relaxation
• Faunal collapse
• Insularization
Conservation Lessons of
Landbridge Islands
The Sundra Shelf after 10,000 yrs
Island
Area
Initial
Present
1000km2 S
S
Borneo 751
153
123
Sumatra 425
139
117
Java
126
113
74
Bali
5
66
19
%
E
20
16
35
71
Land bridge islands
Barro Colorado Island, Panama
1. Hilltop = 15.7 km2 of lowland tropical forest.
2. Isolated in 1914 when Lake Gatun was formed
by construction of the Panama Canal.
3. Knowing area and period of isolation, can
model extinction.
4. 108 species of breeding birds in 1938.
5. Terborgh used land bridge model to predict
17 would be lost in 50 years; really 13 = 12% of
108.
So why does insularization
lead to species loss?
The 3 Step Process of Species Loss and
Extinction Debt
The 3 Step Process of Species Loss and
Extinction Debt
Instantaneous
Sampling
Fast
Isolation
Slow
Area
The 3 Step Process of Species Loss and
Extinction Debt
Instantaneous
Fast
Faster & Greater
Loss as Area
Slow
The 3 Step Process of Species Loss and
Extinction Debt
Instantaneous
Fast
Faster & Greater
Loss as Area
Slow
The 3 Step Process of Species Loss and
Extinction Debt
Instantaneous
Fast
Faster & Greater
Loss as Area
Slow
Extinction debt
Steeper z
Pattern and process
(A.S. Watt 1947)
O Chestnut Tree, Greatrooted blossomer
Are you the leaf, the
blossom, or the bole?
O body swayed to music, O
brightening glance
How can we tell the dancer
from the dance?
--WB Yeats
The Species Loss Equation
SNOW = cANOWz
SORIG = cAORIGz
The Species Loss Equation
SNOW / SORIG = (ANOW / AORIG )
z
The Species Loss Equation
SNOW / SORIG = (ANOW / AORIG )
Critique?
z