Presentation on theme: "Biodiversity and ecosystem functioning Diane Srivastava, UBC Zoology."— Presentation transcript:
Biodiversity and ecosystem functioning Diane Srivastava, UBC Zoology
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?
Human activity: Habitat loss Pollution Overharvesting Conversion of Ecological Capital to Economic Capital Biodiversity loss Ethical and aesthetic costs not measured in $ Economic growth measured in $ Ecological - Economic conflicts prior to Rio ECONOMIC WINECOLOGICAL LOSS how to compare?
Reasons to conserve species diversity: Ethical and aesthetic Evolutionary capital Functional importance in ecosystems & ecosystem services to humans
Ecosystem functions are biological processes that involve the flow of energy and nutrients in, out and through food webs. -Carbon fixation -Water purification -Pollination -Decomposition -Pest suppression -Production of biomass -Nitrogen fixation -Energy flow through food webs Ecosystem services are those ecosystem functions that benefit humans.
The value of the worlds ecosystem services: $33 trillion Costanza et al. 1997 Nature 387: 253-260.
Human activity: Habitat loss Pollution Overharvesting Conversion of Ecological Capital to Economic Capital Biodiversity loss Ecosystem service costs measured in $ Economic growth measured in $ Ecological - Economic conflicts post Rio ECONOMIC WINECOLOGICAL LOSS can compare! Global wetlands: $3.4 billion
Example 1: Pollination Ecosystem service value: $195 billion for global agriculture Pollinator 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. 12- 22% in Europe since 1980s) But does pollinator diversity really increase pollination?
Yes! Pollinator diversity increases pollination and crop yield Pumpkin, Indonesia Coffee, Indonesia Watermelon, California Farms near forests in Costa Rica have 20% greater yield due to higher native pollinator diversity, translating into $60,000 more income for the farmer
Example 2: Water purification Ecosystem service value: New York City $7 billion Algal species diversity Nitrate uptake
Example 3: Carbon fixation Terrestrial plants sequester 2.6 x 10 9 g C per year offsetting 30% of atmospheric carbon emissions Ecosystem service value: set by carbon credits and other instruments, globally in the trillions So plants are valuable – but do we need so many species?
Random loss of species can reduce function (in this case, plant biomass) Tilman, D. et al. 2001. Science 294: 843-5. Yes! Most (86% of 272) experiments show that plant diversity increases plant production ( = C fixation)
Example 4: Stability Ecosystem service value: economic prosperity depends on predictable rates of return on investment. Marine systems: Loss of biodiversity concomitant with increase in risks
Example 4: Stability A system with no consumptive resistance: Mountain pine beetle attack of monoculture forest
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: plants detritivores herbivores predators in both terrestrial and aquatic systems
Losing biodiversity is like losing rivets on an airplane – eventually catastrophic failure Plant production Nutrient uptakeDecomposition
Mechanisms: (1) Niche complementarity Competitive exclusion principle: Species need to be different that each other in order to coexist Species differ in their use of microhabitats and resources, and so complement each other functionally Stonefly Mayfly Sensitivity to disturbance Optimal stream flow
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.
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.
All BDEF experiments are in small, homogeneous plots or bottles. The real world might be different! Problem # 1
If anything, adding realistic amounts of spatial heterogeneity strengthens the BDEF relationship Problem # 1….is not that much of a problem Increasing heterogeneity Heterogeneous streams Homogeneous streams
Problem # 2 Most BDEF experiments are based on random-loss. But we know extinctions arent random! Tend to lose first: Pollution sensitive species Rare species Large species Predators
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. 2009 Nutrient release from marine sediments Species richness
Problem # 3 Sure, diverse ecosystems function better than the average monoculture, but not better than the best monoculture We could optimize carbon sequestration by replacing native forests with ecualyptus monocultures! best
Problem # 3…true only for one function! If we consider optimizing multiple ecosystem functions, there is no magic monoculture
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!