biodiversity and ecosystem functioning diane srivastava, ubc zoology
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 costsnot measured in $
Economic growthmeasured 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 world’s 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 growthmeasured 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
Nitr
ate
up
take
Example 3: Carbon fixation
Terrestrial plants sequester 2.6 x 109 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 uptake Decomposition
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
Op
tima
l str
ea
m fl
ow
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 heterogeneityHeterogeneousstreams
Homogeneousstreams
Problem # 2
Most BDEF experiments are based on random-loss.
But we know extinctions aren’t 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
Nutrientrelease frommarine 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!