Mortality over Time
Population Density Declines
through Mortality
Experimental Evidence:
Self Thinning
Log mean plant weight (w )
Log density (N)
Low
High
Low
High
Change during
one time interval
Experimental Evidence:
Self Thinning
Log mean plant weight (w )
Log density (N)
Low
High
Low
High
Change during
one time interval
Experimental Evidence:
Self Thinning
Log mean plant weight (w )
Log density (N)
Low
High
Low
High
Change during
one time interval
Experimental Evidence:
Self Thinning
Log mean plant weight (w )
Log density (N)
Low
High
Low
High
Change during
one time interval
Experimental Evidence:
Self Thinning
Log mean plant weight (w )
Log density (N)
General pattern
1.
Unimpeded growth
2.
Mortality begins
3.
Similar trajectories exhibited
once thinning starts
4.
At some point thinning slows
1
1
1
1
2
2
2
3
4
Self Thinning
in Thirty
Species
Similar slope
to thinning line
across a range
of species
Attempts to Explain the
Thinning Line
An Intuitive Argument
Two stands of trees
starting at different
densities
An Intuitive Argument
Two stands of trees
starting at different
densities
Thinning occurs as
trees increase in size.
An Intuitive Argument
Two stands of trees
starting at different
densities
Thinning occurs as
trees increase in size.
Trees cannot grow
larger unless enough
space is made
available through
mortality.
Yoda
et al.
(1963)
propose the
“-3/2 Thinning Law”
k
≈
-3/2
“-3/2 Thinning”
k
≈
-3/2
Allometric relationships:
those that scale with
body mass
They posit an underlying
allometric relationship
“-3/2 Thinning”
k
≈
-3/2
They posit an underlying
allometric relationship
•
w
= average individual biomass
•
C = constant
•
N = population density
•
-k = slope of thinning line
“-3/2 Thinning”
k
≈
-3/2
They posit an underlying
allometric relationship
Why 3/2?
An Intuitive Argument
An Intuitive Argument
An Intuitive Argument
An Intuitive Argument
An Intuitive Argument
Biomass
Density
Volume
–>
m
3
Area
m
2
An Intuitive Argument
Biomass
Density
Volume
–>
m
3
Area
m
2
An Intuitive Argument
Biomass
Density
Volume
–>
m
3
Area
m
2
An Intuitive Argument
Biomass
Density
Volume
–>
m
3
Area
m
2
An Intuitive Argument
Biomass
Density
Volume
–>
m
3
Area
m
2
k
≈
-3/2
k
≈
-4/3
Revisiting the
“-3/2 Thinning Law”
X
k
≈
-3/2
k
≈
-4/3
A Revised View of the
Allometric Relationship
Same as the scaling
relationship of body
mass to maximum
density in animals!
A General Interpretation of the Thinning
Relationship
Lemna
Sequoia
A General Interpretation of the Thinning
Relationship
A General Interpretation of the Thinning
Relationship
Permitted
combinations
Prohibited
combinations
Self Thinning Revisited
Log mean plant weight (w )
Log density (N)
General pattern
1.
Unimpeded growth
2.
Mortality begins
3.
Similar trajectories exhibited
once thinning starts
4.
At some point thinning slows
4
?
Self Thinning Revisited
Log mean plant weight (w )
Log density (N)
Growth limited
by space
Growth limited
by resources
Self Thinning Revisited
Log mean plant weight (w )
Log density (N)
Growth limited
by resources
Resource limitation
regulating growth
leads to the “Law of
Constant Yield”
Proof of Constant Yield
with a slope = -1
Log mean plant weight
Log density
Slope
≈
-1
log(N)
log(N-z)
log
Y
N
Y
log
(N-z)
Proof of Constant Yield
with a slope = -1
Log mean plant weight
Log density
Slope
≈
-1
log(N)
log(N-z)
log
Y
N
Y
log
(N-z)
Calculation of slope
Proof of Constant Yield
with a slope = -1
Log mean plant weight
Log density
log(N)
log(N-z)
log
Y
N
Y
log
(N-z)
Calculation of slope
X
X
Proof of Constant Yield
with a slope = -1
Log mean plant weight
Log density
log(N)
log(N-z)
log
Y
N
Y
log
(N-z)
Calculation of slope
= -1
Putting it all together
•
Development of
size hierarchies
•
Thinning
•
Law of Constant Yield