Presentation on theme: "Biodiversity and ecosystem functioning"— Presentation transcript:
1 Biodiversity and ecosystem functioning Diane Srivastava, UBC Zoology
2 In the 20 years since the Conventional on Biological Diversity was signed at Rio …what have we learnt about biodiversity loss? …what have we done about biodiversity loss?
3 Ecological - Economic conflicts prior to Rio Human activity:Habitat lossPollutionOverharvestingECOLOGICAL LOSSECONOMIC WINBiodiversity lossConversion ofEcological Capital to Economic CapitalEthical and aesthetic costsnot measured in $Economic growthmeasured in $how to compare?
4 Reasons to conserve species diversity: Ethical and aestheticEvolutionary capitalFunctional importance in ecosystems& ecosystem services to humans
5 Energy flow through food webs Ecosystem functions are biological processes that involve the flow of energy and nutrients in, out and through food webs.Carbon fixationWater purificationPollinationDecompositionPest suppressionProduction of biomassNitrogen fixationEnergy flow through food websEcosystem services are those ecosystem functions that benefit humans.
6 The value of the world’s ecosystem services: $33 trillion Costanza et al Nature 387:
7 Ecological - Economic conflicts post Rio Human activity:Habitat lossPollutionOverharvestingECOLOGICAL LOSSECONOMIC WINBiodiversity lossConversion ofEcological Capital to Economic CapitalEcosystem service costsmeasured in $Economic growthmeasured in $Global wetlands: $3.4 billioncan compare!
8 Example 1: PollinationEcosystem service value: $195 billion for global agriculturePollinator diversity is declining globally (e.g local diversity of native bees in Europe is half of pre-1980 values)Distribution of bee-dependent plants is declining (e.g % in Europe since 1980s)But does pollinator diversity really increase pollination?
9 Yes! Pollinator diversity increases pollination and crop yield Pumpkin, IndonesiaCoffee, IndonesiaWatermelon, CaliforniaFarms near forests in Costa Rica have 20% greater yield due to higher native pollinator diversity, translating into $60,000 more income for the farmer
10 Example 2: Water purification Ecosystem service value: New York City $7 billionAlgal species diversityNitrate uptake
11 Example 3: Carbon fixation Terrestrial plants sequester 2.6 x 109 g C per year offsetting 30% of atmospheric carbon emissionsEcosystem service value: set by carbon credits and other instruments, globally in the trillionsSo plants are valuable – but do we need so many species?
12 Random loss of species can reduce function Yes! Most (86% of 272) experiments show that plant diversity increases plant production ( = C fixation)Random loss of species can reduce function(in this case, plant biomass)Tilman, D. et al Science 294:
13 Example 4: StabilityEcosystem service value: economic prosperity depends on predictable rates of return on investment.Marine systems:Loss of biodiversity concomitant with increase in risks
14 Example 4: Stability A system with no consumptive resistance: Mountain pine beetle attack of monoculture forest
15 Overall – biodiversity increases ecosystem functioning Meta-analysis of 111 experiments (Cardinale, Srivastava et al. Nature 2006)Biomass production and resource consumption increases with diversity of:plantsdetritivoresherbivorespredatorsin both terrestrial and aquatic systems
16 Losing biodiversity is like losing rivets on an airplane – eventually catastrophic failure Plant productionNutrient uptakeDecomposition
17 Mechanisms: (1) Niche complementarity Competitive exclusion principle: Species need to be different that each other in order to coexistSpecies differ in their use of microhabitats and resources, and so complement each other functionallyOptimal stream flowMayflyStoneflySensitivity to disturbance
18 Mechanisms: (2) Facilitation Species may help each other with function. For example, clover fixes nitrogen which grasses use for biomass production.A field with both clover and grass may therefore be more productive than one with just one of these species.e.g.: Farmers often “intercrop” to get higher yields.
19 Mechanisms: (3) Portfolio effect If species fluctuate independently, their net biomass (or function) may not fluctuate much as individual fluctuations may cancel each other out.Thus more diverse communities may have lower variability than depauperate communities.Rationale taken from economics: to reduce risk, investors “diversify” their stocks.
20 Problem # 1All BDEF experiments are in small, homogeneous plots or bottles. The real world might be different!
21 Problem # 1….is not that much of a problem If anything, adding realistic amounts of spatial heterogeneity strengthens the BDEF relationshipIncreasing heterogeneityHeterogeneousstreamsHomogeneousstreams
22 Problem # 2Most BDEF experiments are based on random-loss.But we know extinctions aren’t random!Tend to lose first:Pollution sensitive speciesRare speciesLarge speciesPredators
23 Problem # 2….is not that much of a problem Expected order of species loss usually exacerbates the effects of species loss on ecosystem function*Functionally important species often the most vulnerable* 9 out of 11 studies that formally compare real and random-loss scenarios, Duffy et al. 2009Nutrientrelease frommarine sedimentsSpecies richness
24 Problem # 3Sure, diverse ecosystems function better than the average monoculture, but not better than the best monocultureWe could optimize carbon sequestration by replacing native forests with ecualyptus monocultures!best
25 Problem # 3…true only for one function! If we consider optimizing multiple ecosystem functions, there is no “magic” monoculture
26 In the 20 years since the Conventional on Biological Diversity was signed at Rio …what have we learnt about biodiversity loss? High certainty about impacts for humanity …what have we done about biodiversity loss? Not enough, over to you today!