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Les conséquences écologiques de l’érosion de la biodiversité
Par :Michel LoreauProfesseur, Département de biologie, Université
McGillChaire de recherche du Canada en écologie théorique
BIENVENUE
Michel LoreauDepartment of Biology, McGill University, Montreal
E-mail: [email protected]
The ecological consequences of biodiversity loss
Loreau, The Challenges of Biodiversity Science (2010)
• The world population increased by a factor of 2.4 between 1950 and 2000
• Average per capita affluence increased by a factor of 2.8 in the same period
• As a result, the gross world product increased sevenfold
The ultimate cause of biodiversity loss: Human environmental impact
Importance of “vertical” diversityRemoval of sea otters
Population explosion of sea urchins
Overgrazing of kelp
•
Extinction of other species living in kelp
•
Increased wave action, coastal erosion and storm damage
•
Evolution of chemical defences in kelp
Sea otter
Sea urchin
Kelp
But what is the ecological significance of “horizontal”
diversity?
Neutral theory Functional redundancy
Niche theory Functional
complementarity
Diversity
Prod
uctiv
ity
Diversity
Prod
uctiv
ity
Separation between community ecology (biodiversity) and ecosystem ecology (ecosystem functioning, management)
Species diversity increases plant biomass production in grasslands
Hector et al., Science 286: 1123–1127 (1999)
Abo
vegr
ound
bio
mas
s (g
/m2 )
Species richness
Tilman et al., Science 294: 843–845 (2001)
A general form of biodiversity– ecosystem functioning relationships?
Cardinale et al., Nature 443: 989–992 (2006)
ΔY = S.ΔRY .M + S.cov(ΔRY, M)
Loreau & Hector, Nature 412: 72–76 (2001)
Net effect = Complementarity effect + Selection effect
Partitioning selection and complementarity in biodiversity experiments
Net effect = Increase in yield above that expected from monoculturesComplementarity effect: Due to improved average performanceSelection effect: Due to dominance by most productive species
Species richness
Biodiversity effects on plant biomass production in BIODEPTH
Loreau & Hector, Nature 412: 72–76 (2001)
Species richness
Selection effect (g1/2/m) Complementarity effect (g1/2/m)
Selection effect (g/m2)
Biodiversity effects on plant biomass production: A meta-analysis
Cardinale et al., PNAS 104: 18123–18128 (2007)
Complementarity effect (g/m2)
The results of biodiversity experiments support niche theory
Neutral theory Functional redundancy
Niche theory Functional
complementarity
Diversity
Prod
uctiv
ity
Diversity
Prod
uctiv
ityNo net biodiversity effectNo complementarity effectNo selection effect
Positive net biodiversity effectPositive complementarity effectVariable selection effect
Biodiversity and ecosystem stability: The insurance hypothesis
Yachi & Loreau, PNAS 96: 1463–1468 (1999)
Based on Tilman et al., Nature 441: 629–632 (2006)Hector et al., Ecology 441: 629–632 (2010)
Species diversity stabilises plant biomass production in grasslands
Species richness Species richness
CV
tota
l bio
mas
s (x
100)
CV
tota
l bio
mas
s
The whole is the sum of its parts, but it obeys different rulesHector et al., Ecology 441: 629–632 (2010)
Population vs. ecosystem stability in grassland plants
Species richness
CV
biom
ass
(x10
0)
Biodiversity as insurance: Mechanisms
1.
Asynchrony of species environmental responses
(= temporal complementarity)
2.
Increase in total biomass
(due to functional complementarity)
Loreau, From Populations to Ecosystems (2010)
in theory
Biodiversity as insurance: Mechanisms in the Cedar Creek experiment
Log Synchrony of environmental
responses
Log Total biomass
Log CV
of total biomass
r2
= 0.27 (P
< 10−9)
r2
= 0.44 (P
< 10−15)
de Mazancourt et al., unpublished results
Inorganic nutrientdepletion zone
L1
PlantP1
qR
kL1kσ1 R
Inorganic nutrient poolR
I
kLSkσS R
…
…cL1P1 L1 P1
HerbivoreH1
cP1H1 P1 H1
CarnivoreC1
cH1C1 H1 C1
PlantPS
cLSPS LS PS
HerbivoreHS
CarnivoreCS
cPSHS PS HS
cHSCS HS CS
Inorganic nutrientdepletion zone
LS
…
cPSH1 PS H1
cHSC1 HS C1
cP1HS P1 HS
cH1CS H1 CS
mPS PS λPS mPS PS
mHS HS λHS mHS HS
mCS CS λCS mCS CS
mP1 P1
mH1 H1
mC1 C1
λP1 mP1 P1
λH1 mH1 H1
λC1 mC1 C1
…
Complex BEF relationships in food webs
Loreau, From Populations to Ecosystems (2010)
Complex BEF relationships in food webs
Species richness
Tot
al b
iom
ass
H1
P1
HS−1
PS−1
HS
PS
…
…
H1
P1
HS−1
PS−1
HS
PS
…
…
Herbivores
Plants
Both plant diversity and
herbivore diversity vary
Herbivore diversity alone
varies
Loreau, From Populations to Ecosystems (2010)
Biodiversity and ecosystem multifunctionality in BIODEPTH
Hector & Bagchi, Nature 448: 188–190 (2007)
Plant species diversity increases forage yield in grasslands
Sanderson et al., Crop Sci. 44: 1132–1144 (2004)Bullock et al., Ecol. Lett. 4: 185–189 (2001)
Forage yield increases in species-rich mixtures as compared with the species-poor mixtures recommended by the UK Ministry across several sites in southern England
Forage yield increases with the number of productive species in Utah
Recommended mixture
Vilà
et al., Ecol. Lett. 10: 241–250 (2007)
⇒ Impact on carbon storage?
Biodiversity increases wood production in Mediterranean forests
Plant species diversity as a reservoir of adaptation to environmental changes
Reich et al., Nature 410: 809–812 (2001)
Genetic diversity increases rice resistance to blast disease
“Disease-susceptible rice varieties planted in mixtures had 89% greater yield and blast was 94% less severe than when they were grown in monoculture. The experiment was so successful that fungicidal spray was no longer applied by the end of the two-year programme.”
Zhu et al., Nature 406: 718–722 (2000)
Ostfeld & Keesing, Conserv. Biol. 14: 722–728 (2000)
Vertebrate host diversity reduces risk of human exposure to Lyme disease
International Center for Integrated Mountain Development (Nepal)
Loss of insect pollinators compensated by human labour in Himalaya
Conclusions
•
Biodiversity loss has significant impacts on ecosystem functioning, in particular:
Horizontal diversity enhances resource use and biomass production through functional complementarity between species
Horizontal diversity stabilises ecosystem properties through a combination of temporal and functional complementarity between species
Conclusions
•
The ecological consequences of biodiversity loss have been vastly underestimated because of the traditional focus on small scales, single trophic levels, and single ecosystem processes
•
Interactions between multiple trophic levels tend to generate complex biodiversity effects; they are potentially
a major source of surprises and uncertainty
•
Most grassland plant species play a significant role in ecosystem functioning when variability across space, time, functions, and environmental drivers is taken into account
Conclusions
•
Biodiversity loss is likely to strongly affect the provision of ecosystem services and is, therefore, a serious threat to human wellbeing and sustainable development