12. Diversity vs., Productivity

Question 1

Structure of the lecture

Answer 1

1. Importance of biodiversity
2. Biodiversity to Ecosystem Function (BEF)
3. Hypothesis:Selection vs., niche complementarity hypothesis
4. Test: Ecotron and field rests
5. Debate: Selection vs., niche complementarity
6. Reconciliation: Cardinale, 2012, Hector and Bagchi, 2001, Isbell, 2001

Question 2

How is understanding biodiversity vs., productivity important for ecosystem services?

1.1

Answer 2

1. Ecosystem processes support beneficial ecosystem services, such as the prevision of nutrients, timber, pollination and productivity
2. Ecosystem functions are natural processes that occur regardless of human presence
3. Ecosystem services are functions that humans derive benefits from

Question 3

What is BEF?

1.2

Answer 3

Biodiversity to ecosystem function (BEF)

Question 4

Darwin’s views on BEF

2.1

Answer 4

Darwin, 1959

Productivity of grass monocultures is lower than that of productivity in a monoculture

Question 5

What is the selection/sampling hypothesis?

3.1

Answer 5

Hector et al., 1999

Based on R-star theory

Postulates that plant communities with a diverse array of species are likely to become dominated by one highly productive species

Few, very productive species control ecosystem function by depleting resources to lowest possible levels

Productive species lead to lower diversity

Question 6

What is the niche-complementarity hypothesis?

3.2

Answer 6

Tilman, 1997

Based on Resource-Ratio theory

Diverse, co-existing species will have different requirements for ecological niches. This leads to more efficient utilisation of available resources through niche differentiation. This increases ecosystem functioning.

Diverse communities have higher communities, since more niches are being filled.

Increasing ecosystem functioning, since there are more species that fill more niches

Question 7

Describe the Ecotron experiment

4.1

Answer 7

Measured plant biodiversity throughout time in a controled manner. Had 3 models for biodiversity at multiple trophic levels: high, medium and low.

Removal of species at each level to measure the impact on productivity

Result: Biodiversity loss led to reduced productivity

Question 8

Describe Tilman’s Cedar Creek experiment

4.2

Answer 8

Field test. Found that more diverse grasslands are more productive

Question 9

How did Huston et al., 1997 attempt to separate niche and complementarity effects?

5.1

Answer 9

By attempting to unravel whether niche complementarity vs., selection theory applies to dominant species.

This is currently sill being debated, and it is uncertain whether BEF relationships are modulated by the traits of dominant species, or the presence of productive species.

Question 10

How did Loreau and Hector, 2001, attempt to unravel selection and niche complementarity effects?

5.2

Answer 10

Argued that the effect of biodiversity is equal to the combined effect of niche complementarity and sampling/selection.

Biodiversity is just as important as niches/resources for ecosystem functioning

There is additive partitionary that occurs as a result of biodiversity

Question 11

How did Cardinale et al., 2012 resolve selection and niche complementarity effects?

5,3

Answer 11

Argued that sampling/selection and niche complementarity are not mutually exclusive. Niche complementarity can be just as strong as, or stronger than, selection.

Question 12

Can some species be functionally redundant?

Argument: YES

6.1

Answer 12

Cardinale et al., 2012

Biodiversity may be saturating, but some species are functionally redundant, and do not contribute to productivity. Loss of the least productive species could lead to higher monoculture yields

Question 13

Are some species functionally redundant?

Argument: No

6.2

Answer 13

Hector and Bagchi, 2007
Isbell et al., 2011

Different species support different functions in different places at different time. Space and time is heterogeneous, and different species are useful at different times.