Effects of biodiveristy on ecosystem functioning
John Bruno
jbruno@unc.edu
962-0263
What is biodiversity?
Genetic
Species & species richness (#/unit area)
Higher taxonomic level
Functional group
What is ecosystem functioning?
Primary production (g/m2)
Primary productivity (g/m2/hour)
Secondary production
Resource use efficiency
Resistance and resiliance, stability
Invasibility
Why ask about the role of biodiversity?
CARNIVORES
HERBIVORES
PLANTS
CARNIVORES
HERBIVORES
PLANTS
Tilman’s study of the effect of plant diversity on productivity
Manipulated plant diversity (0 to 16 species) by adding seeds and extensive weeding
Measured productivity as biomass (above and below ground)
Total biomass (kg/m2)
Plant species richness
Tilman et al. 2001
“Plant biodiversity paradigm”
• Plant diversity has strong positive effects on primary production
• Transgressive overyielding is common
• Selection effects are positive and partially drive biodiversity effects
• The most productive species dominate polycultures
General experimental approach
Monoculture
Mixture (9 species)
Mesocosm growth experimentsIMS, Morehead City, NC
Field growth experiments
Beaufort, NC
Jamaica
Jamaica photosynthesis measurements
Temperature: 27-28ºC
Flow: 4-8 cm/s
Salinity: 35 ppt
Light: 800-1000 uE
25
25
0
0
red algae
Sargassum
Sargassumpolyceratum
polyceratum
Halimeda
Halimedaopuntia
opuntia
Chaetomorpha
Chaetomorphalinum
linum
Caulerpa
Caulerparacemosa
racemosa
Gracilaria
Gracilariadamaecornis
damaecornis
P = 0.35
Laurencia
Laurenciapoiteaui
poiteaui
Gelidiella
Gelidiellaacerosa
acerosa
Galaxaura
Galaxaurarugosa
rugosa
Ceramium
Ceramiumnitens
nitens
Acanthophora
Acanthophoraspecifera
specifera
average
averagemonoculture
monoculture
125
125
100
100
10
10species
species
88species
species
44species
species
22species
species
final
finalwet
wetmass
mass(g)
(g)
Sample size: 10
Duration: 10 days (January 2003)
Starting wet weight: 60g
P < 0.001
75
75
50
50
green algae
brown algae
Effect size
North Carolina
Identity
Richness
RYT
Mesocosm experiment I
0.68
0
1.15
Mesocosm experiment II
0.76
0.01
1.43
Mesocosm experiment III
0.07
0.07
1.21
Field experiment I
0.55
0
1.05
Field experiment II
0.53
0.09
1.24
Photosynthesis experiment
0.28
0
na
Field experiment
0.497
0.003
1.18
Photosynthesis experiment
0.437
0.008
na
Jamaica
-
Fiel
Fie
Mesocos
Mesocos
Mesocos
Mo
200
C ) P < 0.0001,
150
r2
0.5
adj. = 0.73
D) P
0.4
50
0
0.3
0.2
200
150
100
0
50
-100
0
0.1
-50
-50
Monoculture
performance
Monoculture
performance
-100
Proportion
100
-100
Polyculture performance
Negative selection effects
Mo
“New Consensus”
• Plant diversity effects are relatively weak and frequently undetectable
• Compositional effects are much stronger
• Transgressive overyielding is rare
• Selection effects are often negative and reduce net biodiversity effects
• The most productive species rarely dominate polycultures
Englehardt and Richie 2002
Hector et al. 2002-other BIODEPTH papers
Callaway et al. 2003
Hooper and Dukes 2004
Fridley 2002
Downing 2004
Bruno et al. 2005
CARNIVORES
HERBIVORES
PLANTS
Duffy and Hay’s amphipod study
Dr. Emmett Duffy
From Duffy and Hay 2000. Ecological Monographs 10:237-263
Duffy and Hay’s amphipod study
From Duffy and Hay 2000. Ecological Monographs 10:237-263
Duffy’s test of the herbivore diversity hypothesis
Manipulated micrograzer diversity (0-6 species)
Used outdoor mesocosms at VIMS
Measured effects on a variety of ecosystem parameters
(algal biomass, sediment organic content, benthic diversity)
Duffy’s test of the herbivore diversity hypothesis
No grazers
Idotea only
Erichsonella only
All six species
Duffy’s test of the herbivore diversity hypothesis
2.0
10
D
E
C
1.0
AFDM (g)
1.5
I
G
0.5
2) Increasing micrograzer diversity
reduced primary production
E
D
C
0.0
B
5
B
G
I
0
0
2
4
6
0
2
4
6
20
Benthic diversity
B
15
D
E
C
10
I
G
Botryllus biomass
0.6
AFDM (g)
Taxon richness
3) The mechanism appears to be diet
complimentarity
Algal biomass
Grazer biomass
AFDM (g)
Main findings:
1) Most of the herbivores specialized
on one or a few types of algae
0.4
0.2
E
D
G
C
I
B
0.0
Dominance ratio
1.0
2
E
D
C
B
G
4
6
Trophic group
dominance
0.5
I
0.0
0
2
4
6
Grazer species richness
Duffy et al. 2004 Ecology Letters
% dry sediment mass
0
Sediment organic C
0.3
E
0.2
D
C
0.1
0
I
B
G
2
4
6
Grazer species richness
CARNIVORES
HERBIVORES
PLANTS
Predicted effects of increasing predator diversity on
herbivores and plants, categorized as mechanisms
that increase or decrease plant biomass
– Herbivory, + Plant biomass
1) dietary complementarity
2) facilitation among predators
3) selection of a keystone predator
4) reduction of intraspecific competition
5) change in prey behavior (a TMII)
+ Herbivory, – Plant biomass
1) intraguild predation
2) cannibalism
3) predator emigration
4) change in predator behavior
5) omnivory
Predators
((((
shrimp
blennies
_ killifish
crabs
pinfish
+
Herbivores
isopods
_ amphipods
_
Plants
green algae
red algae
brown algae
Omnivorous crab
Omnivorous fish
Carnivorous shrimp
5 species
3 species
Killifish
Blennie
Shrimp
Crab
Pinfish
No predators
Algae wet mass (g)
Herbivores (No.)
500
400
Isopods
300
Amphipods
200
100
0
90
60
30
0
Bruno and O’Connor 2005, Ecology Letters
Number species (S)
1.7
Richness
4.5
4
3.5
1.6
Diversity
1.5
1.4
1.3
1.2
1.1
0.85
0.8
Evenness
0.75
0.7
0.65
5 species
3 species
Killifish
Blennie
Shrimp
Crab
0.6
Pinfish
Simpson's (1-)
C
5
No predators
B
5.5
Shannon-Weiner (H')
A
generalist
carnivores
Bruno and O’Connor 2005, Ecology Letters
A
0.35
Crab
Pinfish
Generalist carnivores
Polycultures
Canonical 2
No predators
0.15
-0.05
0.75
-0.25
-0.25
0
0.25
0.5
0.75
Canonical 1
B
40
ss (g)
Enteromorpha
Hypnea
30
Sargassum + Dictyota
Bruno and O’Connor 2005, Ecology Letters
Byrnes et al.
In press, Ecology Letters
Byrnes et al.
In press, Ecology Letters
Byrnes et al.
In press, Ecology Letters
Kelp crab
urchin
Finke and Denno
In press, Ecology Letters