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Light:Nutrient Balance
And the Dynamics of
Pelagic Ecosystems
Jim Elser
Department of Biology
Arizona State University
With thanks to...
Jotaro Urabe, Kyoto University
Tom Andersen, NIVA
Bob Sterner, U of Minnesota
Tom Chrzanowski, U Texas
David Schindler, U of Alberta
Pat Hassett, Ohio University
H. Hayakawa, Lake Biwa Research Institute
Marcia Kyle, ASU
John Schampel, U of Minnesota
Wataru Makino, Kyoto University
Shariar Anwar, ASU
Mike Paterson, Freshwater Institute
Dave Findlay , Freshwater Institute
Ken Mills, Freshwater Institute
Michael Turner, Freshwater Institute
Everett Fee, Canmore, Alberta
Stephanie Guildford, Freshwater Institute
Neil MacKay, ASU
Paul Frost, ASU
Linda Gudex, ASU
Jessie Clasen, ASU
Nick George, U of Minnesota
Takehito Yoshida, Kyoto University
Traci Main, ASU
Dean Foster, ASU
Tessie Tibbets, ASU
Amy Waggener, ASU
Craig Herbold, USC
Staffs of:
Experimental Lakes Area
Trout Lake Biological Station
U of Notre Dame Environmental Research Center
Center for Ecological Research, Kyoto University
This work was funded by the NSF.
And a little bit by NASA.
Goals for Today’s Talk
For the non-ecologists (and ecologists who haven’t been paying attention):
- introduce the theory of ecological stoichiometry (ES)
- show how ES is useful in understanding food-web dynamics
For the ecologists:
- change the way you think about the role of light in food webs
- change the way you think about the competitive exclusion principle
For everyone:
- suggest applications of ES and light:nutrient balance to
global climate change
Astrobiology
What would happen to cows
if there wasn't so much sunlight?
Expectations from a 9-year old ecologist
Stephen Elser
resident specialist
on Pokémon ecology
Primary Production,
Autotroph Biomass
What would happen to secondary production
if solar radiation were reduced?
Expectations from single-currency ecological theory
Solar Radiation
High
Secondary Production,
Herbivore Biomass
Low
Low
Solar Radiation
High
(CXNYPZ)inorganic + (CXNYPZ) autotroph + light -> Q (CXNYPZ)' autotroph + (CXNYPZ)’ inorganic
(CXNYPZ)prey + (CXNYPZ) predator -> Q (CXNYPZ) predator + (CXNYPZ)’ waste
From: Elser, J.J., and J. Urabe. 1999. The stoichiometry of consumer-driven nutrient recycling: theory, observations, and consequences.
Ecology 80: 735-751.
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Ecological Stoichiometry of Autotrophs and Herbivores
In Freshwater and Terrestrial Ecosystems
Terrestrial foliage vs. freshwater seston
% Observations
60
T: 36freshwater
(406)
terrestrial
F: 10 (267)
50
40
terrestrial
freshwater
30
20
10
<5
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
>100
0
Biomass C:N
% Observations
50
T: 968 (413)
F: 307 (203)
40
30
20
10
3250
>3500
3000
2750
2500
2250
2000
1750
1500
1250
750
Biomass C:P
25
T: 28.3 (332)
F: 30.2 (267)
20
15
10
60
55
>65
Biomass N:P
50
45
40
35
30
25
20
15
5
0
10
5
<5
% Observations
1000
500
250
<250
0
From: Elser, J.J., W.F. Fagan, R.F. Denno, D.R. Dobberfuhl, A. Folarin, A. Huberty, S. Interlandi, S.S. Kilham, E. McCauley, K.L. Schulz, E.H.
Siemann, and R.W. Sterner. 2000. Nutritional constraints in terrestrial and freshwater food webs. Nature 408: 578-580.
Ecological Stoichiometry of Autotrophs and Herbivores
In Freshwater and Terrestrial Ecosystems
Terrestrial foliage vs. freshwater seston
Terrestrial insects vs. freshwater zooplankton
% Observations
60
T: 36 freshwater
(406)
terrestrial
F: 10 (267)
50
40
terrestrial
freshwater
30
T: 6.5 (124)
F: 6.3 (38)
20
10
<5
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
>100
0
Biomass C:N
% Observations
50
T: 968 (413)
F: 307 (203)
40
30
T: 116 (27)
F: 124 (40)
20
10
3250
>3500
3000
2750
2500
2250
2000
1750
1500
1250
750
Biomass C:P
25
T: 28.3 (332)
F: 30.2 (267)
20
15
T: 26.4 (22)
F: 22.3 (37)
10
60
55
>65
Biomass N:P
50
45
40
35
30
25
20
15
5
0
10
5
<5
% Observations
1000
500
250
<250
0
From: Elser, J.J., W.F. Fagan, R.F. Denno, D.R. Dobberfuhl, A. Folarin, A. Huberty, S. Interlandi, S.S. Kilham, E. McCauley, K.L. Schulz, E.H.
Siemann, and R.W. Sterner. 2000. Nutritional constraints in terrestrial and freshwater food webs. Nature 408: 578-580.
Stoichiometric Imbalance Impairs Herbivores
In Freshwater and Terrestrial Ecosystems
Freshwater herbivore (Daphnia)
Terrestrial herbivore (Pieris)
25
20
15
10
5
mean
Pieris rapae 10%
0
0
10
20
30
90%
(59)
40
Biomass C:N in Food
GGE = (Mass of New Biomass Produced)
(Mass Ingested)
But do such effects occur in nature?
From: Elser, J.J., W.F. Fagan, R.F. Denno, D.R. Dobberfuhl, A. Folarin, A. Huberty, S. Interlandi, S.S. Kilham, E. McCauley, K.L. Schulz, E.H.
Siemann, and R.W. Sterner. 2000. Nutritional constraints in terrestrial and freshwater food webs. Nature 408: 578-580.
But Does High Seston C:P Reduce Daphnia Growth in Nature?
An experimental test...
remov e
zooplankton
+PO
4
spike
f eed to Daphni a babies
f or 6 h
Daily
collect
lakew ater
no spike
(control)
After 5 days, measure final body weights
and calculate juvenile growth rates.
Performed for 3 lakes at the Experimental Lakes Area:
L239 and L240 (high seston C:P)
L979 (low seston C:P)
back to regular
lakew ater for
remaining 18 h
repeat for
5 days
But Does High Seston C:P Reduce Daphnia Growth in Nature?
L239
Seston C (µM)
120
L240
L979
initial
after 6 h
100
80
60
40
20
Seston C:P (molar)
0
1
2
4
1
2
4
1
2
initial
after 6 h
1200
1000
800
600
400
200
0
1
2
Day
4
1
2
Day
4
1
2
Day
0.4 p < 0.03
0.4 p < 0.01
0.4
0.3
0.3
0.3
0.2
0.2
0.2
0.1
0.1
0.1
p < 0.05
-1
growth rate (d )
But Does High Seston C:P Reduce Daphnia Growth in Nature?
L239
0.0
C
+P
L240
0.0
L979
0.0
C
+P
C
“Hai.”
From: Elser, J.J., H. Hayakawa, and J. Urabe. 2001. Nutrient limitation reduces food quality for zooplankton:
responses of Daphnia growth to short-term phosphorus amendment of natural seston. Ecology 82: 898-903.
+P
What Regulates Autotroph Nutrient Limitation and C:N:P In Nature?
and
What Are the Ecological Consequences?
50% treatment
100
25 % treatment
40
marine
30
30
20
10
20
0
10
0
50
100
150
200
250
300
% Observations
40
Biomass C:P
3250
>3500
2000
2250
2500
2750
3000
750
1000
1250
1500
1750
<250
250
500
0
(modified from Elser and Hassett 1994, Nature 370: 211-213, Elser et
al. 2000, Nature 408: 578-580.)
From: Sterner, R.W. and J.J. Elser . 2002. Ecological Stoichiometry: The Biology of Elements from Molecules to
the Biosphere. Princeton University Press, Princeton, NJ.
What Regulates AutotrophNutrient Limitation and C:N:P In Nature?
and
What Are the Ecological Consequences?
100 % treatment
25 % treatment
The Light : Nutrient Project
Autotroph C : Nutrient Ratio Increases
(Nutrient Content Declines)
Under Nutrient Limitation
% Maxim um Gr ow th Rate
25
50
75
100
12
1200
800
10
Percent Nitrogen
Cellular C:P
1600
400
Cellular N:P
0
120
80
8
6
4
40
2
0
0
0.2
0.4
0.6
0.8
1.0
-1
Spe cific Gr ow th Rate (d )
P-limited Alga
LOW
HIGH
N "Stress"
N-limited Wheat
(Monochrysis lutheri)
(f rom Greenwood 1976)
(f rom Goldman et al. 1979)
From: Sterner, R.W. and J.J. Elser . 2002. Ecological Stoichiometry: The Biology of Elements from Molecules to
the Biosphere. Princeton University Press, Princeton, NJ.
Autotroph C : Nutrient Ratio Increases
(Nutrient Content Declines)
With Increasing Light Intensity
P-limited Growth
N:C
(µg : mg)
300
P:C
(µg : mg)
300
200
100
50
N:P
(µg : µg)
N:C
(µg : mg)
5
30
0
0.4
0.8
Spe cific Gr ow th Rate (d
4.0
%N
3.0
HN / HP
HN / LP
LN / HP
LN / LP
ab
-1
)
Nutrient-limited
Cyanobacterium
100
0
30
(Synechococcus linearis)
(no relat ionships)
20
From Healey (1985)
12
8
4
0
0.4
0.8
1.2
Spe cific Gr ow th Rate (d
ab
b
b b
a a
0.3
b
0.2
a
a
a
b
0.0
Low
Light
)
0.0
a
Nutrient-limited
Red pine
(Pinus resinosa)
ab
0.1
1.0
High
-1
0.4
a
a
2.0
200
0
1.2
%P
P:C
(µg : mg)
incr easi ng li ght
10
N:P
(µg : µg)
Cellular Ratios (by mass)
15
N-limited Growth
From Elliot and White (1994)
High
Low
Light
From: Sterner, R.W. and J.J. Elser . 2002. Ecological Stoichiometry: The Biology of Elements from Molecules to
the Biosphere. Princeton University Press, Princeton, NJ.
temperatur e
temperatur e
deep
The Light:Nutrient Hypothesis:
Causes
shallow
mixed layer depth
li ght
li ght
high
low
water clarity
high
low
nutrient supply
50
marine
30
30
high
low
20
10
20
0
10
0
50
100
150
200
250
300
% Observations
40
40
I m : nutrient supply
high
low
Biomass C:P
3250
>3500
2000
2250
2500
2750
3000
750
1000
1250
1500
1750
<250
250
500
0
grow th capacity (µ
high
)
max
low
actual grow th rate (µ)
high
low
Relative Grow th Rate (µ:µ
high
low
Based on: Sterner, R.W., J.J. Elser, E.J. Fee, S.J. Guildford, and T.H. Chrzanowski.
1997. The light:nutrient balance in lakes: the balance of energy and materials
affects ecosystem structure and process. Am. Nat. 150: 663-684.
)max
Particulate C:P
high
low
I m: nutrient supply
high
low
Particulate C:P
The Light:Nutrient Hypothesis:
Consequences
high
low
"Ecological efficiency" (2°/1°)
strong
weak
Strength of trophic cascade
high
low
Efficiency of P recycling
strong
weak
Based on: Sterner, R.W., J.J. Elser, E.J. Fee, S.J. Guildford, and T.H. Chrzanowski.
1997. The light:nutrient balance in lakes: the balance of energy and materials
affects ecosystem structure and process. Am. Nat. 150: 663-684.
Phytoplankton-bacteria
competition
Evaluating The Light:Nutrient Hypothesis:
A Mix of Strategies
Simple
Controlled
Replicated
Short
Small
Artificial
Analytical
model
Simulation
model
Complex
Uncontrolled
Unreplicated
Long
Large
Natural
Lab
flask
Small indoor
microcosms
Big indoor
microcosms
Field
microcosms
Whole-ecosystem
manipulation
Field
sampling
Correlation Test of the Light:Nutrient Hypothesis
The Northwest Ontario Lake Size
Series (NOLSS)
Gr e e n Lak e
Or ange Lake
Linge Lak e
Mus clow Lak e
Sydne y Lake
Tr out Lak e
89 ha
167 ha
706 ha
2220 ha
5750 ha
34,700 ha
From: Sterner, R.W., J.J. Elser, E.J. Fee, S.J.
Guildford, and T.H. Chrzanowski. 1997.
The light:nutrient balance in lakes: the
balance of energy and materials affects
ecosystem structure and process. Am. Nat.
150: 663-684.
Correlation Test of the Light:Nutrient Hypothesis
Regional Differences in Seston C:P
600
1000
P < 0.001
P < 0.05, r2 = 0.45
800
600
400
400
200
200
0
Wis c ons in
ELA
0
Wisconsin
ELA
0 2 4 6 8 10 12
rel. I m: TP
OK, but correlations are just correlations...
Based on: Hassett, R.P., B. Cardinale, L.B. Stabler, and J.J. Elser. Ecological stoichiometry of N and P in lakes and
oceans with emphasis on the zooplankton-phytoplankton interaction. Limnol. Oceanogr. 42: 648-662.
Experimental Test of the Light:Nutrient Hypothesis
Experiment by Urabe and Sterner
Biomass (mg C / L)
6 10
1.6 µM P
2
5
0
0 0
0
Size after 5 d (µg)
0.10 µM P
3
10
30
Algal
Biomass
2
15
4
10
5
1
P:C ratio
Daphniagrowth
20
5
10
0
0
10
100
10
100
Light Intensity (µE / sq m / sec)
From: Urabe J, Sterner RW. 1996. Regulation of herbivore growth by the balance of light and nutrients. PNAS 93:8465-8469.
Seston C:P (molar)
Experiment by
Sterner, Lampert, and Co.
Seston C (µM)
Experimental Test of the Light:Nutrient Hypothesis
From: Sterner RW, Clasen J, Lampert W, Weisse T. 1998. Carbon:phosphorus stoichiometry and food chain production. Ecology Letters 1:146-150.
Experimental Test of the Light:Nutrient Hypothesis
Experiment by Urabe, Elser, and Andersen
Ambient
(I)
Shaded
(~7% I)
0
0.75
1.5
3
6
12 µg P /L
 Enclosures were 1-m diameter, 4-m deep. Each was covered with Plexiglas to
remove UV.
 Enclosures sampled every 5 d for 4.5 weeks.
 Seston [C], C:P, zooplankton biomass were monitored (among other things)
 Daphnia growth on enclosure seston was assessed at 3.5 weeks.
Experimental Test of the Light:Nutrient Hypothesis
Seston C (mg C /L)
+ 1 s.e.
Experiment by Urabe, Elser, and Andersen
Ambient light
Seston C:P
+ 1 s.e.
Shaded
Enriched P +1 (µg / L)
From: Urabe, J., M. Kyle, W. Makino, T. Yoshida, T.
Andersen, and J. J. Elser. 2002. Reduced light
increases herbivore production due to
stoichiometric effects of light:nutrient balance.
Ecology: in press.
Experimental Test of the Light:Nutrient Hypothesis
Seston C (mg C /L)
+ 1 s.e.
Experiment by Urabe, Elser, and Andersen
Ambient light
Zooplankton (µg dw / L)
+ 1 s.e.
Seston C:P
+ 1 s.e.
Shaded
From: Urabe, J., M. Kyle, W. Makino, T. Yoshida, T.
Andersen, and J. J. Elser. 2002. Reduced light
increases herbivore production due to
stoichiometric effects of light:nutrient balance.
Ecology: in press.
Enriched P +1 (µg / L)
Experimental Test of the Light:Nutrient Hypothesis
Experiment by Urabe, Elser, and Andersen
100
100
Daphnia biomass
Daphnia
( µg d.w.Biomass
1 -1 )
(µg / L)
a
b
Ambient
light
10
10
1
1
0.1
0.1
0.2
0.4
0.6
Se s ton abundance
( µg C l -1 )
Shaded
0
200
400
C:P atomic ratio
From: Urabe, J., M. Kyle, W. Makino, T. Yoshida, T. Andersen, and J. J. Elser. 2002. Reduced light
increases herbivore production due to stoichiometric effects of light:nutrient balance. Ecology: in press.
600
Experimental Test of the Light:Nutrient Hypothesis
Undiluted seston
ambient light
shaded
60% diluted seston
ambient light
shaded
Residuals
Growth of
juvenile Daphnia
on undiluted and
diluted (60%) seston
from the enclosures.
Growth Rate (per d)
Experiment by Urabe, Elser, and Andersen
Theoretical Test of Light:Nutrient Effects
Model of Loladze, Kuang and Elser (modified from model of T. Andersen)
(
x' (t) = bx 1 -
Grazer
(
x
min[K, (P - qy)] / q
y' (t) = emin 1, min
(P - qy) / x
q
) - f (x)y
) f (x)y - dy
Producer
From: Loladze, I, Y. Kuang, and J.J. Elser. 2000. Stoichiometry in producer-grazer systems: linking energy flow and element
cycling. Bull. Math. Biol. 62: 1137-1162.
Theoretical Test of Light:Nutrient Effects
Model of Loladze, Kuang and Elser (modified from model of T. Andersen)
light
light
light
From: Loladze, I, Y. Kuang, and J.J. Elser. 2000. Stoichiometry in producer-grazer systems: linking energy flow and element
cycling. Bull. Math. Biol. 62: 1137-1162.
Theoretical Test of Light:Nutrient Effects
Model of Loladze, Kuang and Elser (modified from model of T. Andersen)
Grazer
light
From: Loladze, I, Y. Kuang, and J.J. Elser. 2000. Stoichiometry in producer-grazer systems: linking energy flow and element
cycling. Bull. Math. Biol. 62: 1137-1162.
Experimental Test of the Light:Nutrient Hypothesis
"Aquatron" Experiment (summer 2000) by Urabe and Elser
Aquatron Dynamics
High Light
(40 µE / sq m / s)
(310 µE / sq m / s)
(380 µE / sq m / s)
50
A
B
1
0.5
Food biomass (mg C l -1 )
6
C
Daphnia
Algal
P:C
10
4
5
2
Algal C
0
1
0
0
30
60
90
0
30
60
90
0
30
60
90
Days
C transfer
efficiency:
~30%
C transfer
efficiency:
~7%
Urabe, J., J.J. Elser, M. Kyle, T. Sekino and Z. Kawabata. 2002. Herbivorous animals can mitigate unfavorable
ratios of energy and material supplies by enhancing nutrient recycling. Ecology Letters: in press.
P:C ratio of food (x 10 -3 )
Consumer biomass (mgC l -1 )
1.5
Low Light
(Extra)
High Light
Aquatron Dynamics
10
10
A
normal density
dependence
Brood size (eggs /(eggs
adult)
/ female)
Size
Brood
8
C
7.5
6
5
Low Light
4
2.5
2
0
0
0.1
Daphnia biomass (mg dw / L)
1
0
2
4
6
Seston abundance (mg C l -1)
Daphnia (mg dw / L)
10
10
B
7.5
8
D
what is this?
7.5
5
5
2.5
2.5
High Light
Urabe, J., J.J. Elser, M. Kyle,
T. Sekino and Z. Kawabata.
2002. Herbivorous animals
can mitigate unfavorable ratios
of energy and material
supplies by enhancing nutrient
recycling. Ecology Letters: in
press.
0
0
0.1
Daphnia biomass (mg dw / L)
Daphnia
(mg dw / L)
1
0
500
1000
C:P ratio
1500
20
Aquatron Dynamics
Low Light
High Light
(Extra)
High Light
(40 µE / sq m / s)
(310 µE / sq m / s)
(380 µE / sq m / s)
B
C
100
Daphnia (indiv. l-1 )
A
D. pulicaria
10
1
D. magna
0.1
10
50
90
10
50
90
10
50
90
Days
exclusion
coexistence
Urabe, J., J.J. Elser, M. Kyle, T. Sekino and Z. Kawabata. 2002. Herbivorous animals can mitigate unfavorable
ratios of energy and material supplies by enhancing nutrient recycling. Ecology Letters: in press.
temperatur e
temperatur e
deep
shallow
mixed layer depth
li ght
li ght
high
low
water clarity
high
The Light:Nutrient Hypothesis:
Causes

Unbalanced supplies of light and
nutrients result in unbalanced growth of
phytoplankton, generating increased
C:nutrient ratios at the base of the pelagic
food web.
low
nutrient supply
high
low
I m : nutrient supply
high
low
grow th capacity (µ
high
)
max
low
actual grow th rate (µ)
high
low
Relative Grow th Rate (µ:µ
high
low
From: Sterner, R.W., J.J. Elser, E.J. Fee, S.J. Guildford, and T.H. Chrzanowski.
1997. The light:nutrient balance in lakes: the balance of energy and
materials affects ecosystem structure and process. Am. Nat. 150: 663-684.
)max
Particulate C:P
high
low
The Light:Nutrient Hypothesis:
Consequences
I m: nutrient supply
high
low
Particulate C:P

This is bad news for herbivores.
Man, this stuff
is HORRIBLE!
high
low
"Ecological efficiency" (2°/1°)
strong
weak
Strength of trophic cascade
high
low
Efficiency of P recycling
strong
weak
From: Sterner, R.W., J.J. Elser, E.J. Fee, S.J. Guildford, and T.H. Chrzanowski.
1997. The light:nutrient balance in lakes: the balance of energy and
materials affects ecosystem structure and process. Am. Nat. 150: 663-684.
Phytoplankton-bacteria
competition
Applications and Implications
Light:Nutrient Balance
And the Global Ocean
From: Karl, D.1998. A sea of change: biogeochemical variability
in the North Pacific Subtropical Gyre Ecosystems 2: 181214.
Light:Nutrient Balance and Global Change
 Under future climate scenarios in the continental boreal regions
(Schindler 1998), runoff to lakes will likely decrease. Effects of
such shifts on lakes remain unclear.
 However, such climate changes will likely lower external nutrient
supply while simultaneously raising light intensity (due to lower
DOC inputs). Light:nutrient supply may become increasingly
unbalanced.

These effects are analogous to effects of elevated pCO2 in
terrestrial systems and appear to be driven by similar
mechanisms.
Evolution in microbe-based ecosystems:
Desert springs as analogues for the early development
and stabilization of ecological systems
PI’s:
Tom Dowling, Biology
Luis Eguiarte, UNAM
Jim Elser, Biology
Bill Fagan, Biology
Other participants:
John Schampel, Biology
Evan Carson, Biology
Trent McDowell, Geology
Brian Wade, Microbiology
James Watts, Biology
Jack Farmer, Geology
Ferran Garcia-Pichel, Microbiology
Valeria Souza, UNAM
C. Tang, Cal. Acad. Sci.
Cuatro Cienegas as Seen from Space
Aerial Views
Some photos courtesy of: http://www.utexas.edu/depts/tnhc/.www/fish/dfc/cuatroc/
Stromatolites at Cuatro Cienegas
thin section
high magnification
Some photos courtesy of:
http://www.utexas.edu/depts/tnhc/.www/fish/dfc/cu
atroc/
Higher Food Web Components
Hydrobid snails (endemic)
(incl. CaCO3 deposits that crawl and
CaPO4 apatite deposits that swim)
Two-line pupfish (endemic)
Cichlid (endemic)
(fish-eating form)
Cichlid (endemic)
(mollusk-eating form)
Photos courtesy of: http://www.utexas.edu/depts/tnhc/.www/fish/dfc/cuatroc/
Grazer Biomass
Grazer Biomass
A Stoichiometric Constraint
on the Cambrian Explosion?
Conclusions
Light:nutrient balance has major effects on food webs by altering
the stoichiometric balance between autotrophs and herbivores.
 These effects can lead to counter-intuitive outcomes in the food
web (e.g. decreased secondary production with increased light,
facilitation instead of competition among herbivores).


Various anthropogenic pertubations, including global change,
simultaneously impact multiple factors in ecosystems.
Ecological stoichiometry can help understand and predict these
impacts.
Ecological / evolutionary theory will be more effective when it
fully acknowledges the chemical basis of living things.
Thanks for listening….
…and thanks to Stephen for helping.