Download Jiang_Feb_22_2008

Biodiversity and Ecosystem
Functioning: Looking Back and
Moving Forward
Jiang, Lin
School of Biology
Georgia Institute of Technology
Email: [email protected]
Outline
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Current knowledge on biodiversity and ecosystem functioning
(BEF)
 Mechanisms: niche complementarity and positive selection
effects
Problems associated with current BEF studies
 An important mechanism that has received relatively little
attention: the negative selection effect
Hypothesis: multiple forms of BEF relationships.
 My own experimental data
 Literature survey
Biodiversity and stability:
 Question: Does predation alter the relationship between
biodiversity and stability?
Species extinction: past, current, and
future trends
Definitions

Biodiversity: genetic, taxonomic, or functional diversity.
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Species richness: the number of species.
Ecosystem functioning: stocks of energy and materials,
fluxes of energy or material processing, and stability of
stocks or rates over time

Biomass, decomposition, the ability to support consumer
populations, temporal stability of biomass.
Hypothetical relationships between
Ecosystem functioning
biodiversity and ecosystem functioning
Type 1
Species richness
Vitousek and Hooper 1993
Hypothetical relationships between
Ecosystem functioning
biodiversity and ecosystem functioning
Type 1
Type 2
Species richness
Vitousek and Hooper 1993
Hypothetical relationships between
Ecosystem functioning
biodiversity and ecosystem functioning
Type 1
Type 2
Type 3
Species richness
Vitousek and Hooper 1993
Cedar Creek
Experiment
Tilman et al. 2001
BIODEPTH
Experiment
Hector et al. 1999
Ecosystem functioning
The commonly observed relationship between
biodiversity and ecosystem functioning
Type 2
Species richness
Mechanisms for the positive BEF
relationship

Niche
Complementarity

Niche differentiation
among species allows
diverse communities to
utilize available
resources more
completely (Tilman et al.
1997)
No niche overlap
Low diversity
High diversity
Mechanisms for the positive BEF
relationship

The positive selection (or
sampling) effect
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Competitively dominant
Positive correlation between
species competitive ability
and its contribution to
ecosystem functioning.
Increasing diversity increases
the probability that
communities are dominated
by functionally important
species (Aarssen 1997,
Huston 1997, Tilman et al.
1997)
Low diversity
High diversity
The positive selection effect appears to be the
primary mechanism behind positive relations
between biodiversity and community biomass
(Cardinale et al. 2006)
Problems with current BEF experiments

Most BEF experiments are short-term.

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Last less than one generation of experimental
organisms.
Most BEF experiments focus on biomass
production.

Patterns on biomass production may not be
generalized to other ecosystem variables.
The negative selection effect
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No positive correlation
between species
competitive ability and its
contribution to ecosystem
functioning.
Increasing diversity
increases the probability
that communities are
dominated by functionally
insignificant species.
Competitively dominant
Low diversity
High diversity
Ecosystem functioning
Strong negative selection effects can lead to no
effects of biodiversity on ecosystem
functioning
Type 3
Species richness
Ecosystem functioning
Strong negative selection effects can even lead
to negative effects of biodiversity on
ecosystem functioning
Species richness
A simple simulation study to
illustrate the negative selection effect
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A regional pool of 20 species
Two ecosystem functions: community biomass and an undefined
non-biomass function
For each species, its biomass and contribution to the undefined
function are independently and normally distributed
Better competitors, which attain greater biomass, always exclude
worse competitors
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No complementarity effects
Ten different species compositions at each diversity level (2, 6,
10, 14 and 18 species) were randomly drawn from the species
pool
100 simulation experiments
A positive BEF relation for community biomass vs.
diverse BEF relations for the non-biomass function
100
biomass
non-biomass function
Percentage
80
60
40
20
0
negative
neutral
positive
Three new types of BEF relations
Ecosystem functioning
Type 1
Type 2
Type 3
Species richness
Jiang et al., Oikos, in press
Bacterial diversity experiment:
negative selection effects
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Two-way factorial design:
 Bacterial richness: 1, 2, 3, 4 species from a four-species pool
containing Bacillus cereus (Bc), Bacillus pumilus (Bp),
Frigoribacterium sp. (F), and Serratia marcescens (Sm)
 The presence/absence of a bacterivorous ciliate: Tetrahymena
pyriformis
Ecosystem properties:
 Total bacterial biomass
 Decomposition of particulate organic matter (wheat seeds)
 Consumer (Tetrahymena) abundance
Experimental Timeline
Microcosm
setup
Consumer
inoculation
Week1
Week2
Bacterial
inoculation
Sampling
Week3
Wheat seed
introduction
Week
4-6
Week7
Four Bacterial Species
Frigoribacterium sp.
Serratia marcescens
Bacillus pumilus
Bacillus cereus
Tetrahymena pyriformis
10
10
c o n tro l
p re d a tio n
3
T otal bacterial biovolum e (log 10 (m /m l))
Total bacterial biovolume increased with
diversity due largely to positive selection
effects
9
9
8
8
7
7
6
6
5
5
4
4
1
2
3
B a c te ria l ric h n e s s
4
B
c
B
p
F
S
m
B
cB
p
B
cF Sm pF Sm Sm pF Sm Sm Sm Sm
B
c
p
F cB Bp cF pF pF
B
B
B
c
B
B cB
B
B
B a c te ria l c o m p o s itio n
Jiang, Ecology, 2007
Testing the mechanisms (Loreau 1998)
Dmax
OT  max( M i )

max( M i )
OT : the total yield of a polyculture
max(Mi) : the maximum monoculture yield of the species in the mixture
Dmax > 0: the complementarity effect present
Dmax = 0: the positive selection effect present
Dmax < 0: the negative selection effect present
Bootstrapped 95% confidence
intervals (CI) of Dmax
Jiang, Ecology, 2007
No bacterial diversity effect on decomposition
due to negative selection effects
0 .5
0 .5
c o n tro l
Fraction of wheat seed loss
g ra z in g
0 .4
0 .4
0 .3
0 .3
0 .2
0 .2
0 .1
0 .1
0 .0
0 .0
1
2
3
B a c te ria l ric h n e s s
4
B
c
B
p
F
m p F m F m m F m m m m
S cB B c cS B p pS FS B p pS FS FS FS
c
B
B
B
B cB B c B p B p
c
B
B
B a c te ria l c o m p o s itio n
Jiang, Ecology, 2007
Bootstrapped 95% confidence
intervals (CI) of Dmax
Jiang, Ecology, 2007
3
C onsum er population biovolum e (log 10 (µm /m l))
No bacterial diversity effect on consumer
abundance due to negative selection effects
5
5
4
4
3
3
2
2
1
2
3
B a c te ria l ric h n e s s
4
B
c
B
p
F
S
m
B
cB
p
B
cF Sm pF Sm Sm pF Sm Sm Sm Sm
B
c
p
F cB Bp cF pF pF
B
B
B
c
B
B cB
B
B
B a c te ria l c o m p o s itio n
Jiang, Ecology, 2007
Bootstrapped 95% confidence
intervals (CI) of Dmax
Jiang, Ecology, 2007
Abundant evidence suggests that
increasing prey diversity tends to reduce
predator abundance
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The negative selection effect: diverse communities are
more likely to contain unpalatable or inedible prey,
which can become dominant in the presence of
predators.
Ideas in different fields:
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the resource concentration hypothesis in agricultural pest
control (Andow 1991).
the variance in edibility hypothesis in community ecology
(Duffy et al. 2007)
the dilution effect in disease ecology (Keesing et al. 2006)
Existing decomposer diversitydecomposition experiments
Jiang et al., Oikos, in press
Summary
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The negative selection effect may contribute
significantly to the BEF relationship.
The positive BEF relationship for aggregate community
biomass may not be generalized to other ecosystem
functions.
Positive BEF relations should be uncommon when
examining ecosystem functions for which species
competitive ability is not a reliable indicator of its
functional impact.
Future BEF experiments should pay more attention to
ecosystem functions other than biomass.
Biodiversity and stability

Multiple concepts of stability (Pimm 1984,
1991)
Temporal stability: the reciprocal of temporal
variability (i.e., how much a variable fluctuates over
time)
 Resistance
 Resilience
 Persistence
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Stability can be measured at both population
and community levels.
Biodiversity and stability: ideas and
theories
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Early conceptual ideas that increasing biodiversity tends
to increase stability
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Theoretical predictions that increasing biodiversity
tends to reduce population stability
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MacArthur (1955), Elton (1958), Odum (1959), Margalef
(1969)
May (1973), Lehman and Tilman (2000)
Theoretical predictions that increasing biodiversity
tends to increase community stability (e.g., stability of
total community biomass)
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Tilman (1999), Ives and Hughes (2002)
Biodiversity and stability: empirical
findings
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Common positive diversity-stability relationships at the
community level
 McNaughton 1977, Dodd et al. 1994, McGrady-Steed et al.
1997, McGrady-Steed and Morin 2000, Valone and Hoffman
2003a, Caldeira et al. 2005, Steiner 2005, Steiner et al. 2005a,
b, Romanuk et al. 2006, Tilman et al. 2006, Vogt et al. 2006,
Zhang and Zhang 2006
Various diversity-stability relationships at the population
level
 Positive: Romanuk and Kolasa 2004, Kolasa and Li 2003,
Valone and Hoffman 2003b, Romanuk et al. 2006, Vogt et al.
2006
 Neutral: McGrady-Steed and Morin 2000, Romanuk and
Kolasa 2002, Steiner et al. 2005a
 Negative: Gonzalez and Descampus-Julien 2004, Tilman et al.
2006.
Does predation affect the relationship
between biodiversity and stability?
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Positive and neutral effects of biodiversity on
population stability are typical for experiments
conducted in systems involving multiple trophic levels
Hypothesis: Increasing diversity may promote
population stability in the presence of predators
via the weak interaction effect.
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McCann et al. (1998): large oscillations of strong-interacting
predator-prey populations may be damped when additional
prey species that interact weakly with predators are present.
A microcosm experiment
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Two-way factorial design:
The presence/absence of a predatory ciliate:
Lacrymaria sp.
 A prey diversity gradient (1, 2, 3 species) with three
bacterivorous ciliates: Colpidium striatum (C), Halteria
sp. (H), and Tetrahymena pyriformis (T).
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Experimental duration: one month
Species abundance data collected every 2-3 days
The strength of predator-prey
interactions differs among prey species
Population density (log10(#/ml+1))
Low
High
Intermediate
5
5
5
Halteria
4
4
4
3
3
3
2
2
2
1
1
0
0
control
predation
1
0
0
5 10 15 20 25 30
Day
Tetrahymena
Colpidium
0
5 10 15 20 25 30
Day
0
5 10 15 20 25 30
Day
Predation altered the relationship between
diversity and community stability
SD (log10(total community biovolume))
2.0
control
predation
1.5
R2 = 0.25, P = 0.0173
1.0
0.5
0.0
0
1
2
Species richness
3
4
SD (log10(population density))
Predation altered the relationship between
biodiversity and population stability
Tetrahymena
Colpidium
Halteria
1.0
1.0
control
predation
0.8
2.0
0.8
1.5
R2 = 0.35, P = 0.016
0.6
0.6
1.0
0.4
0.4
0.2
0.2
0.0
0.0
0.5
0
1
2
3
Species richness
4
R2 = 0.30, P = 0.035
0
1
2
3
Species richness
4
R2 = 0.61, P = 0.0005
0.0
0
1
2
3
Species richness
4
Summary
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The relationship between biodiversity and
stability is context-dependent.
In the absence of predators, increasing biodiversity
reduced population stability but had little effect on
community stability.
 In the presence of predators, weak predator-prey
interactions helped stabilize population and
community dynamics in more diverse communities.
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Ecosystem function (stability included)
The take-home message
Type 1
Type 2
Type 3
Species richness
Acknowledgments
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Georgia Institute of Technology
National Science Foundation
Shivani Patel, Hena Joshi