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

- 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

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 complementarity 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

Decomposition rapid

Absorption rapid

Volatiles released

Stimulate condensation and precipitation

Rainforests feed themselves and water themselves.

CUT FOREST DOWN

REDUCE RAINFALL... REDUCE NUTRIENTS

INCREASE FIRE

Select for fire-adapted grasses.... rainforest doesn't come back....

RAINFOREST

(wet, few fires)

GRASSLAND

(dry, many fires)

"Multiple Stable States"

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