Les conséquences écologiques de l érosion de la biodiversité Par :

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Randell Ross
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Département de biologie, Université McGill Chaire

1 Les conséquences écologiques de l érosion de la biodiversité Par : Michel Loreau Professeur, Département de biologie, Université McGill Chaire de recherche du Canada en écologie théorique BIENVENUE

2 The ecological consequences of biodiversity loss Michel Loreau Department of Biology, McGill University, Montreal

3 Heading for a global biodiversity crisis

4 Heading for a global biodiversity crisis

5 Proximate drivers of biodiversity loss

4 between 1950 and 2000 Average per capita affluence increased by a factor of 2.

6 The ultimate cause of biodiversity loss: Human environmental impact 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 Loreau, The Challenges of Biodiversity Science (2010)

7 Why does biodiversity matter?

8 Biodiversity, ecosystem functioning, and human wellbeing

Importance of vertical diversity Removal of

kelp Increased wave action, coastal erosion

9 Importance of vertical diversity Removal of sea otters Sea otter Population explosion of sea urchins Overgrazing of kelp Sea urchin Kelp Extinction of other species living in kelp Increased wave action, coastal erosion and storm damage Evolution of chemical defences in kelp

10 But what is the ecological significance of horizontal diversity? Separation between community ecology (biodiversity) and ecosystem ecology (ecosystem functioning, management) Neutral theory Functional redundancy Niche theory Functional complementarity Productivity Productivity Diversity Diversity

11 Cedar Creek biodiversity experiment

12 BIODEPTH biodiversity experiment

13 Species diversity increases plant biomass production in grasslands Aboveground biomass (g/m 2 ) Species richness Hector et al., Science 286: (1999) Tilman et al., Science 294: (2001)

14 A general form of biodiversity ecosystem functioning relationships? Cardinale et al., Nature 443: (2006)

15 The controversy over mechanisms Loreau et al., Science 294: (2001)

16 Partitioning selection and complementarity in biodiversity experiments ΔY = S.ΔRY.M + S.cov(ΔRY, M) Net effect = Complementarity effect + Selection effect Net effect = Increase in yield above that expected from monocultures Complementarity effect: Due to improved average performance Selection effect: Due to dominance by most productive species Loreau & Hector, Nature 412: (2001)

17 Biodiversity effects on plant biomass production in BIODEPTH Selection effect (g 1/2 /m) Complementarity effect (g 1/2 /m) Species richness Species richness Loreau & Hector, Nature 412: (2001)

18 Biodiversity effects on plant biomass production: A meta-analysis Selection effect (g/m 2 ) Complementarity effect (g/m 2 ) Cardinale et al., PNAS 104: (2007)

19 The results of biodiversity experiments support niche theory Neutral theory Functional redundancy Niche theory Functional complementarity Productivity Productivity Diversity No net biodiversity effect No complementarity effect No selection effect Diversity Positive net biodiversity effect Positive complementarity effect Variable selection effect

20 Biodiversity and ecosystem stability: The insurance hypothesis Yachi & Loreau, PNAS 96: (1999)

21 Species diversity stabilises plant biomass production in grasslands CV total biomass (x100) CV total biomass Species richness Hector et al., Ecology 441: (2010) Species richness Based on Tilman et al., Nature 441: (2006)

22 Population vs. ecosystem stability in grassland plants CV biomass (x100) Species richness The whole is the sum of its parts, but it obeys different rules Hector et al., Ecology 441: (2010)

23 Biodiversity as insurance: Mechanisms in theory 1. Asynchrony of species environmental responses (= temporal complementarity) 2. Increase in total biomass (due to functional complementarity) Loreau, From Populations to Ecosystems (2010)

24 Biodiversity as insurance: Mechanisms in the Cedar Creek experiment r 2 = 0.27 (P < 10 9 ) Log CV of total biomass r 2 = 0.44 (P < ) Log Synchrony of environmental responses Log Total biomass de Mazancourt et al., unpublished results

25 Complex BEF relationships in food webs λ C1 m C1 C 1 m C1 C 1 Carnivore C 1 Carnivore C S m CS C S λ CS m CS C S λ H1 m H1 H 1 m H1 H 1 c H1C1 H 1 C 1 Herbivore H 1 c H1CS H 1 C S c HSC1 H S C 1 Herbivore H S c HSCS H S C S m HS H S λ HS m HS H S λ P1 m P1 P 1 m P1 P 1 c P1H1 P 1 H 1 Plant P 1 c P1HS P 1 H S c PSH1 P S H 1 Plant P S c PSHS P S H S m PS P S λ PS m PS P S c L1P1 L 1 P 1 Inorganic nutrient depletion zone L 1 c LSPS L S P S Inorganic nutrient depletion zone L S kσ 1 R kl 1 kσ S R kl S I Inorganic nutrient pool R qr Loreau, From Populations to Ecosystems (2010)

26 Complex BEF relationships in food webs H 1 H S 1 H S H 1 H S 1 H S P 1 P S 1 P S P 1 P S 1 P S Total biomass Both plant diversity and herbivore diversity vary Plants Herbivores Herbivore diversity alone varies Species richness Loreau, From Populations to Ecosystems (2010)

27 Biodiversity and ecosystem multifunctionality in BIODEPTH Hector & Bagchi, Nature 448: (2007)

28 Biodiversity and ecosystem multifunctionality in grasslands Isbell et al., unpublished results

29 Biodiversity and ecosystem multifunctionality in grasslands Isbell et al., unpublished results

30 From ecosystem functioning to ecosystem services

Plant species diversity increases forage yield in grasslands Forage yield increases in species-rich mixtures as compared with the species-poor mixtures recommended by the UK Ministry across several

31 Plant species diversity increases forage yield in grasslands 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 Bullock et al., Ecol. Lett. 4: (2001) Sanderson et al., Crop Sci. 44: (2004)

32 Biodiversity increases wood production in Mediterranean forests Impact on carbon storage? Vilà et al., Ecol. Lett. 10: (2007)

33 Plant species diversity as a reservoir of adaptation to environmental changes Reich et al., Nature 410: (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

34 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: (2000)

35 Vertebrate host diversity reduces risk of human exposure to Lyme disease Ostfeld & Keesing, Conserv. Biol. 14: (2000)

36 Loss of insect pollinators compensated by human labour in Himalaya International Center for Integrated Mountain Development (Nepal)

37 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

38 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

39 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

40 If you want to know more Princeton University Press (2010)

What is the ecological evidence for a link between biodiversity and ecosystem services? James Bullock & Phil Martin Centre for Ecology & Hydrology

What is the ecological evidence for a link between biodiversity and ecosystem services? James Bullock & Phil Martin Centre for Ecology & Hydrology Evidence vs Belief Millennium Ecosystem Assessment Biodiversity