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

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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

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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!