Transcript Biodiversity and ecosystem function

If biodiversity is so precious and important,
then why is it so threatened?
 Distinguish between physical agents of biodiversity loss,
and the underlying policy and social reasons
 Existence of trade-offs- those actions harmful to one
component of nature also provide valuable societal
benefits
(Tilman 1999)
 Much of current environmental policy is rooted in policy
developed for an older and much different world
Dr. John A. Finn
University of Reading
Social, cultural and economic driving forces that
cause reduced biodiversity need addressing:
a) difference between value to individual and society need
to be removed, especially where irreversible damage
caused
b) reform social and economic policies that drive species
loss
c) more research and institutions for biodiversity
conservation. Science has an integral role in contributing
to policy reform; “Society invests in science because
science benefits society”
Folke et al, 1996
Dr. John A. Finn
University of Reading
Human population in the biodiversity hotspots.
 25 biodiversity hotspots that have exceptionally high
species richness and endemicity. Are also very
threatened by human activities. (Cincotta et al. Nature
404: 990-992.)
 Overhead- indicates relationship between biodiversity
hotspots and population pressure
Dr. John A. Finn
University of Reading
“The world that exists in 100 and 1000
years will be of human design, whether
deliberate or haphazard. Principles of
design need to be based on science and
ethics”
Tilman 1999
Dr. John A. Finn
University of Reading
References for previous section:
 Biological diversity, ecosystems and the human scale.
1996. Folke et al. Ecological Applications 6: 1018- 1024.
(electronically available through library)
 Causes, consequences and ethics of biodiversity. 1999
Tilman, D. Nature 405: 208-211. (electronically available
through registration at Nature website
http://www.nature.com/nature/info/insights.
html)
 Human population in the biodiversity hotspots. Cincotta et
al. Nature 404: 990-992.
Dr. John A. Finn
University of Reading
Biodiversity and ecosystem function:
pattern, process and prospects
Dr. John A. Finn
Department of Agriculture,
The University of Reading
Experimental reductions in biodiversity
"On average, plants contain less than half a gram of
carbon per square metre. Yet this thin veneer of living
matter sandwiched between a 100km deep lithosphere and
a 100-km high atmosphere manages to cycle about 60
gigatonnes (60 x 1015) of carbon per year between the
biosphere, lithosphere and atmosphere. Clearly the Earth's
biota has staggering capability to affect our environment.”
But this perspective overlooks a critical feature of plant
life: this green slime consists of more than a quarter of a
million species. What, if any, is the role of such
extraordinary diversity? ”
Naeem [1999]
Dr. John A. Finn
University of Reading
Ecosystem function
Hypothetical relationships between diversity and ecological processes
Redundant
low
Rivet
high
low
Idiosyncratic
high
low
Species richness
Dr. John A. Finn
University of Reading
high
Relationship between diversity and function
 Null hypothesis: ecosystem function is insensitive to
species additions or deletions (the trivial case)
Ecosystem
function
low
high
Species richness
Dr. John A. Finn
University of Reading
What are ecosystem effects of a reduction in diversity?
 Rivet: all species contribute to the integrity of an ecosystem in a
small but significant way such that a progressive loss of species
steadily damages ecosystem function.
Ecosystem
function
low
high
Species richness
Dr. John A. Finn
University of Reading
Relationship between diversity and function
 Redundant:the contribution of additional species is redundant
above a critical level
Ecosystem
function
low
high
Species richness
Dr. John A. Finn
University of Reading
Relationship between diversity and function
 Idiosyncratic hypothesis: ecosystem function changes
unpredictably as species richness changes
Ecosystem
function
low
high
Species richness
Dr. John A. Finn
University of Reading
 BIODiversity and Ecosystem Processes in Terrestrial
Herbaceous systems: an EU funded project examining the
importance of biodiversity for ecosystem functioning.
 Diversity gradient of:
species richness (five levels)
functional group richness (three levels)
Simulated loss of plant species from background level to
single species
 Eight European sites, 2m X 2m plots, ~60 plots each site
 measured: above-ground biomass, soil nutrients, insect
herbivory, weed invasion etc.
Dr. John A. Finn
University of Reading
Novel contribution of BIODEPTH:
 Experimentally varies diversity at a local scale: diversity is
a determinant variable
 Varies composition within each diversity level
 Independently varies species richness and functional group
richness
 Measures a variety of ecosystem processes, not just yield
 Designed to permit analyses that identify contribution of
sampling effect and complementarity, i.e. the mechanisms
by which diversity exerts and influence
 Replicated experiment conducted at several sites across a
large spatial scale
Dr. John A. Finn
University of Reading
1500
Germany
1500
Portugal
1500
Switzerland
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1000
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Ireland
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Sweden
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UK (Sheffield)
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UK (Silwood)
ANOVA: P < 0.01
ANOVA: P < 0.001
0
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Greece
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D e c r e a s in g
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s p e c ie s
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( lo g
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s c a le )
Decreasing species richness (log2 scale)
Dr. John A. Finn
University of Reading
 The previous slide show the relationship between diversity
and aboveground biomass at each of the local sites
(countries). When each data set from individual sites were
analysed individually, the relationship was best described
by a variety of models: linear (Portugal and Switzerland);
curvilinear ( Germany, Sweden, Sheffield); ANOVA (Ireland
and Silwood).
Dr. John A. Finn
University of Reading
Aboveground Biomass (g/m )
2
1500
1000
Germany
Ireland
UK
Switzerland
500
Portugal
Sweden
Greece
0
32
16
8
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1
Decreasing Plant Species Richness
Dr. John A. Finn
University of Reading
 The previous slide shows a ‘meta-analysis’ (combined
analysis) of all of the data simultaneously. The analyses
attributed variation mostly to location (30% of variation),
diversity (20%) and species composition (40%). There
was no significant diversity*location interaction. This
means that the shape of the relationship between biomass
and diversity at each site did not differ significantly. Thus,
overall, the relationship was described as a log-linear
reduction in biomass as diversity decreased. This
corresponds to a general reduction of about 80 g biomass
per sq. metre for each halving of species richness in
European grasslands.
Dr. John A. Finn
University of Reading
Explanations for differences between single sites and meta-analysis
 (i) all sites conform to the same underlying pattern seen in the overall
analysis, and differences between individual sites are due to reduced
sample size and statistical power
 (ii) sites do differ in their responses, but the overall analysis is not
powerful enough to reveal a significant location-by-species richness
relationship
 (iii) a significant general pattern emerges despite differences in detail
at individual locations; while at any single location the effect of
changes in species richness may vary from strong (e.g. Portugal,
Switzerland) to undetectable (e.g. Greece), but on average we would
expect productivity to decline as species richness declines.
Dr. John A. Finn
University of Reading
Aboveground biomass (g/m )
2
800
b
700
600
500
8 species
4 species
2 species
11 species
400
300
3
2
1
Decreasing functional group richness
Dr. John A. Finn
University of Reading
Processes to explain relationships between
diversity and ecosystem function
 ‘Sampling effect’ or ‘selection probability effect’
 Niche complementarity
 Positive species interactions e.g. mutualisms
Dr. John A. Finn
University of Reading
Processes (contd)
The Sampling Effect
 The sampling effect:
more diverse communities have a greater probability of containing
and becoming dominated by, a highly productive species.
Important biological property of ecological systems OR
artefact of species richness experiments and random
assemblages, a ‘hidden treatment’
Dr. John A. Finn
University of Reading
How might biodiversity relate to ecosystem function?
 2. Niche complementarity- ecological differences between
species lead to more complete utilisation of available
resources in more diverse communities.
Granivorous ants/rodents feeding on different sized seeds;
microhabitat preferences in animals
Different rooting depths by plants, different degrees of shadetolerance etc.
 3. Mutualisms- A reduction in positive mutualistic
interactions among species in more depauparate and
simplified communities.
Dr. John A. Finn
University of Reading
Niche complementarity: Within- and between- FG diversity
FG 1
SP 1
FG 2
SP 3
SP 2
SP 4
FG 3
Ecological differences between species lead to more complete utilisation of
available resources in more diverse communities. Differences between species
of different functional groups are expected to be greater than differences
Dr. John A. Finn
between species of the same FG
University of Reading
Aboveground biomass (g/m )
2
800
b
700
600
500
8 species
4 species
2 species
11 species
400
300
3
2
1
Decreasing functional group richness
Dr. John A. Finn
University of Reading
The insurance hypothesis: More diverse assemblages will have a greater
probability of having species that are adapted to changed conditions
Stable conditions
Environmental fluctuation
Contribution
of each
species to
ecosystem
function
7 spp
1 spp
6 spp
1 spp
John A. Finn
Species richness Dr.
University of Reading
The Insurance Hypothesis: more diverse assemblages have a greater
probability of containing species that are adapted to changed conditions
10 sp.
process
rate
1 sp.
constant
conditions
2 sp.
4 sp.
variable
conditions
Dr. John A. Finn
University of Reading
The Insurance Hypothesis: more diverse assemblages have a greater
probability of containing species that are adapted to changed conditions
10 sp.
ecological
process
4 sp.
2 sp.
1 sp.
constant
conditions
variable
conditions
Dr. John A. Finn
University of Reading
Further references on function-diversity work:
 Hector, A. et al. (1999) Plant diversity and productivity experiments in
European grasslands. Science, 286, 1123-1127. (BIODEPTH project)
 Hooper, D.U. (1998) The role of complementarity and competition in
ecosystem responses to variation in plant diversity. Ecology, 79, 704 - 719.
 Jonsson, M. and Malmqvist, B. 2000. Ecosystem process rate increases
with animal species richness: evidence from leaf-eating, aquatic insects. Oikos 89: 519-523.
 Tilman, D., Knops, J., Wedin, D., Reich, P., Ritchie, M. & Siemann, E.
(1997a) The influence of functional diversity and composition on
ecosystem processes. Science, 277, 1300-1302.
Dr. John A. Finn
University of Reading