Download current problems of ecosystem ecology and biodiversity theory

CURRENT PROBLEMS OF
ECOSYSTEM ECOLOGY AND
BIODIVERSITY THEORY
CURRENT PROBLEMS OF
ECOSYSTEM ECOLOGY
AND BIODIVERSITY THEORY
January Weiner
Jagiellonian University
Underground part of a grassland ecosystem trophic web:
Grazing and detritivorous trophic chains are interwoven;
Many functional groups; even more species
SPECIES DIVERSITY
AND
ECOSYSTEM FUNCTIONING
„...It has been
experimentally proved, if a
plot of ground be sown
with one species of grass,
and a similar plot be sown
with several distinct
genera of grasses, a
greater number of plants
and greater weight of dry
herbage can be raised in
the latter than the former
case...”
Bayreuth
conference
1993
„Diversity begets stability”
controversy
•
•
•
•
•
Elton, MacArthur ...
May (1972), Goodman (1975)
Doubts...
Concept of „biodiversity” (biotic diversity)
„biodiversity and ecosystem functioning”
1994
P.M. Vitousek, D.U.Hooper:
Biological diversity and terrestrial
ecosystem biogeochemistry
Ecosystem function
may depend on:
NUMBER OF HITS ON KEYWORDS
„BIODIVERSITY” + „ECOSYSTEM FUNCTION”
(Scopus)
A. Species number (redundancy)
4000
3500
B. Species abundances (domination
structure)
3000
2500
2000
1500
1000
C. Species functional specifity
(complementarity)
500
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
0
HYPOTHETICAL
EFFECTS of
DIVERSITY
REDUCTION
upon
ECOSYSTEM
FUNCTIONING
DAVID TILMAN
(>50 HIYPOTHESES)
Naeem, Lorau, Inchausti 2002
MANIPULATIVE FIELD EXPERIMENTS
(CEDAR CREEK LTER SITE)
• ARTIFICIALLY
ASSEMBLED COMMUNITIES
• REMOVAL EXPERIMENTS
BIODIVERSITY EFFECT
UPON:
• ECOSYSTEM FUNCTIONS
• RESISTANCE/RESILIENCE/
STABILITY
JONATHAN LEVINE
MICHEL LOREAU
Cedar Creek
Long Term
Ecological
Research site
(LTER-site)
(Minnesota, USA)
LONG-TERM EXPERIMENTS
ECOSYSTEM FUNCTIONS MONIOTORED:
•PRODUCTIVITY
•BIOMASS (ABOVEGROUND,
UNDERGROUND)
• NUTRIENTS (CYCLING,
RETENTION)
• NITROGEN (UPTAKE, RETENTION)
•DECOMPOSITION
•CO2 (FLUX, RESPIRATION)
Schwartz et al.. 2000
EXPERIMENTS on
STABILITY (RESISTANCE/RESILIENCE)
Plots with 16 species reached 2.7 × more biomass than
monocultures (repeated in various combinations)
Tilman 1999
Ecology 80:1455-1474
Plant cover and soil
nitrogen uptake are greater
in plots with more species
NPP was more resistant to
drought and recovered faster in
the plots with many species
HYPOTHESES EXPLAINING THE EFFECT
OF BIODIVERSITY UPON ECOSYSTEM
FUNCTIONING
ECOLOGICAL
MECHANISMS OF
BIODIVERSITY EFFECT
• complementarity
• facilitation
„SAMPLING
EFFECT”:
At high initial number of
species there is increased
probability that a species
of particularly high
productivity and
competitive competences
may occur among them
(Computer simulations)
STATISTICAL ARTEFACT
•„sampling effect”
Two competing species (A i B), each of wchich has specific
requirements conc. 2 kinds of resources (1 i 2)
Amount of resource 2
Tillman’s resource competence model
(„scramble competition”)
A
B
A
CB = CA
A
A eliminates B
Only A
B
Amount of resource 2
Amount of resource 2
Amount of resource 1
B eliminates A
equilibrium (stable?)
Only B
B
Amount of resource 1
Niche differentiation:
At a higher habitat
heterogeneity the number of
species and the total
community biomass increase
Amount of resource 1
The effect of species characters upon ecosystem
functioning: nitrogen mineralisation rate depends on grass
species, at the same nitrogen availability (100 g N/m2)
(Wedin i Tilman 1990)
Facilitation:
The effect of nitrogen-fixing tree (Myrica faya)
on nitrogen balance in a montane forest
ecosystem (Hawaii)
Plant cover and
biomass increase
with species
number;
a repeatable effect
(Cedar Creek
experiment, Tilman &
al.. 2001)
Utilization of
available nitrogen
increases with
species number
Nitrogen uptake depending on species number
(Tilman et al.. 1996)
(Cedar Creek
experiment, Tilman &
al.. 2001)
Diversity (S) and stability
A. Drought resistance (Cedar Creek
experiment, Tilman & Downing 1994):
biomass before/after drought (increases with
S)
B. Year to year coef. of variance of total
community biomass (decreases with S);
Tilman 1996, 1999
C. Coeff. of variance of the biomass of
particular species (increases with S); Tilman
1996
DROUGHT RESISTANCE
(Cedar Creek experiment, Tilman & Downing 1994): log (biomass
before/after drought ratio) (increases with S)
EXPERIMENTAL ECOSYSTEMS
(„MICROCOSMS”, „ECOTRONS”)
Other similar
experiments
A. Total biomass of artificial
plant communities in greenhouse
(increases with S)
B. Field experiment in California
grasslands: community biomass
increases with the number of
functional groups
BIODEPTH:
METHODOLOGICAL
CONTROVERSIES
BIODiversity and
Ecosystem Process in
Terrestrial Herbaceous
Ecosystems
„BIODEPTH” SITE
IN PORTUGAL
RESULTS OF THE BIODEPTH EXPERIMENT
(Hector at al.. 2002)
BIODEPTH EXPERIMENT:
NET EFFECT OF BIODIVERSITY
COMPLEMENTARITY ***
SELECTION
(Hector at al.. 2002)
Effect of functional „dissimilarity” of macro-detritivores on
soil ecosystem (microcosm experiment).
Science 306, Nov. 2004
respiration
respiration
Litter mass loss
Litter mass
loss
2002
EXPERIMENTAL EVIDENCE FOR FUNCTIONAL
EFFECTS OF COMMUNITY DIVERSITY
EFFECT
OBSERVATIONAL
EXPERIMENTAL
ECOSYSTEM FUNCTIONING
POSITIVE
NEGATIVE
N O EFFECT
5
3
3
15
3
2
RESILIENCE/RESISTANCE)
POSITIVE
NO EFFECT
1
?
2
1
VARANCE
POSITIVE
NEGATIVE
1
5
Schwartz et al.. 2000