Effects of biodiveristy on ecosystem functioning

John Brunojbruno@unc.edu962-0263

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

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)

Plant species richness

Tot

al b

iom

ass

(kg/

m2 )

Tilman et al. 2001

• 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

“Plant biodiversity paradigm”

General experimental approach

Mixture (9 species)Monoculture

Mesocosm growth experiments-

IMS, 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

red algae green algae

brown algae

Sample size: 10

Duration: 10 days (January 2003)

Starting wet weight: 60g

P < 0.001P = 0.35

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

Jamaica

Field experiment 0.497 0.003 1.18

Photosynthesis experiment 0.437 0.008 na

Effect size

Monoculture performance

Negative selection effects

• 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 2002Hector et al. 2002-other BIODEPTH papersCallaway et al. 2003Hooper and Dukes 2004Fridley 2002Downing 2004Bruno et al. 2005

“New Consensus”

CARNIVORES

HERBIVORES

PLANTS

Duffy and Hay’s amphipod study

From Duffy and Hay 2000. Ecological Monographs 10:237-263

Dr. Emmett Duffy

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 VIMSMeasured effects on a variety of ecosystem parameters (algal biomass, sediment organic content, benthic diversity)

No grazersNo grazers Idotea onlyIdotea only

Erichsonella onlyErichsonella onlyAll six speciesAll six species

Duffy’s test of the herbivore diversity hypothesis

0 2 4 6

AFDM (g)

0.0

0.5

1.0

1.5

2.0

0 2 4 6

AFDM (g)

0

5

10Algal biomass

0 2 4 6

% dry sediment mass0.1

0.2

0.3

0 2 4 6

Taxon richness10

15

20

Benthic diversity

Grazer biomass

Sediment organic C

EB

D GIC

E BD G

I

C

E

B

D

G

I

C

E

BD

G

I

C

AFDM (g)

0.0

0.2

0.4

0.6 Botryllus biomass

E

B

D G

IC

E

B

D

G

IC

Grazer species richness

0 2 4 6

Dominance ratio0.0

0.5

1.0

Trophic groupdominance

Grazer species richness

Main findings:1) Most of the herbivores specialized

on one or a few types of algae

2) Increasing micrograzer diversity reduced primary production

3) The mechanism appears to be diet complimentarity

Duffy’s test of the herbivore diversity hypothesis

Duffy et al. 2004 Ecology Letters

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 ((((

Herbivores

Plants

_

_

shrimp blennies killifish crabs pinfish

isopods amphipods

green algae red algae brown algae

_

+

Omnivorous fish

Omnivorous crab

Carnivorous shrimp

Bruno and O’Connor 2005, Ecology Letters

Bruno and O’Connor 2005, Ecology Letters

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 DennoIn press, Ecology Letters