Transcript A. Productivity

IV. Productivity, Diversity, and Stability
A. Productivity
A. Productivity
1. Gross Primary Productivity?
A. Productivity
1. Gross Primary Productivity
Total photosynthetic productivity;
CO2 + H20 -----> Glucose + O2
A. Productivity
2. Net Primary Productivity?
A. Productivity
2. Net Primary Productivity
NPP = GPP - respiration
(Plants use some of the energy they
absorb; it is not stored as biomass. NPP is
only the amount stored as new biomass.
B. Diversity - Relationships with Productivity
B. Diversity - Relationships with Productivity
1. Productivity increases diversity
B. Diversity - Relationships with Productivity
1. Productivity increases diversity
- QUANTITATIVE EFFECT
If you have more productivity at the base
of a food web, then you can build a longer
food chain (adding additional levels AND
species)…. And then get keystone effects.
B. Diversity - Relationships with Productivity
1. Productivity increases diversity
- QUALITATIVE EFFECT
An increase in productivity may also occur
because more types of food have been added.
This may allow for more specialization at the
next trophic level - and the coexistence of
more species.
B. Diversity - Relationships with Productivity
1. Productivity increases diversity
2. Diversity increases productivity
- Sampling Effects
More diverse communities are more likely to
contain the most productive species, and thus
raise the total productivity.
- Niche Complementarity
More diverse communities are more likely to
contain different types of species that use
different types of energy... thus more efficiently
harvesting the available energy
Monoculture
They all need the same
things at the same
concentrations; have to
place them far apart to
reduce competition.
Polyculture
Combinations of different plants can be
planted at higher density, and they use
different "niches" and coexist. Even if
abundance of "most productive" species,
drops, this loss can be offset.
- Positive Interactions
More diverse communities may contain
species that benefit other species, and thus
increase the productivity of the whole
community
Monoculture
They all need the same
things at the same
concentrations; have to
place them far apart to
reduce competition.
Polyculture
Nitrogen fixing legumes
(beans) nutrify the soil,
increasing the growth of
other plants
without
beans
with
beans
Diversity and Productivity in a Long-Term Grassland Experiment Tilman, et
al. 2001. Science 294. 843 - 845
Dotted line is biomass in a monoculture of the most productive species. Higher
productivity than this, at higher richness values, means niche complementarity or
positive effects must be occurring.
Diversity and Productivity in a Long-Term Grassland Experiment Tilman, et
al. 2001. Science 294. 843 - 845
Dotted line is biomass in a monoculture of the most productive species. Higher
productivity than this, at higher richness values, means niche complementarity or
positive effects must be occurring.
So, many
random
assemblages
of multiple
species have
biomass
above that of
the most
abundant
monoculture.
Diversity and Productivity in a Long-Term Grassland Experiment Tilman, et
al. 2001. Science 294. 843 - 845
Dotted line is biomass in a monoculture of the most productive species. Higher
productivity than this, at higher richness values, means niche complementarity or
positive effects must be occurring.
So, many
random
assemblages
of multiple
species have
biomass
above that of
the most
abundant
monoculture.
And we might
expect
greater niche
complementa
rity in natural
systems…
- Effects of Genetic Diversity
Example Crutsinger, et al. 2006. Science 313: 966-968.
Methods:
- 63 1m2 plots, each containing 12 plants of all goldenrod.
- The plants in a plot represent either 1, 3, 6, or 12
genotypes, randomly selected from a pool of 21 genotypes.
- Example Crutsinger, et al. 2006.
Science 313: 966-968.
Results:
1: ANPP correlated with number
of genotypes in plot.
- Example Crutsinger, et al. 2006.
Science 313: 966-968.
Results:
1: ANPP correlated with number
of genotypes in plot.
2: Total insect species diversity,
and diversity of herbivores and
predators, correlate with ANPP
and number of genotypes per
plot.
- Example Crutsinger, et al. 2006.
Science 313: 966-968.
Results:
3. The effects were non-additive;
there were more arthropods
(and herbivores and predators)
in 6 and 12 species plots than
predicted by adding the richness
values of the monocultures.
- Example Crutsinger, et al. 2006.
Science 313: 966-968.
Results:
5: Increase in herbivorous
insects due to both MORE food
(ANPP - quantitative effect) and
DIFFERENT food (niche
differentiation - qualitative
effect).
- Example Crutsinger, et al. 2006.
Science 313: 966-968.
Results:
6: Increase in predator richness
due to increase in herbivore
richness, not AMOUNT of food.
Some herbivores were only
associated with some
genotypes.
C. Effects on Stability
C. Effects on Stability
1. Types
- "resistance to change"
- "resilience after change"
C. Effects on Stability
1. Types
2. Relationships with diversity
- more diverse communities are less
susceptible to single "types of
disturbance" - (a pest, a flood, a drought) because the many species are unlikely to
be sensitive to the same thing.
C. Effects on Stability
Biodiversity and Ecosystem
Functioning: Current Knowledge
and Future Challenges. Loreau, et
al. 2001. Science 294: 804 - 808
As richness increases,
communities become less variable
(more stable).
C. Stability
1. Types
2. Relationships with diversity
- diverse communities may recover more
rapidly, too (resilience).... but they may not.
Fisheries ... yes
Rain forest... maybe not
Stimulate condensation
and precipitation
Volatiles released
Rainforests feed
themselves and
water themselves.
Decomposition
rapid
Absorption rapid
CUT FOREST
DOWN
Select for fire-adapted
grasses.... rainforest
doesn't come back....
REDUCE RAINFALL...
REDUCE NUTRIENTS
INCREASE FIRE
RAINFOREST
(wet, few fires)
"Multiple
Stable States"
GRASSLAND
(dry, many fires)
We are dependent on the environment
for food and resources. Ideally, we
would like a STABLE, PRODUCTIVE
supply of these resources.... right??
FEAST
FAMINE
(We don't want "boom and bust", "feast
and famine" scenarios....)
FEAST
FAMINE
We are dependent on the environment
for food and resources. Ideally, we
would like a STABLE, PRODUCTIVE
supply of these resources.... right??
(We don't want "boom and bust", "feast
and famine" scenarios....)
STABILITY
?
PRODUCTIVITY
We are playing jenga with our life
support systems...
de Ruiter et al. 2005. Food Web
Ecology: Playing Jenga and
Beyond Science 309:68 - 71
de Ruiter et al. 2005. Food Web Ecology: Playing Jenga and Beyond Science
309:68 - 71