Plant diversity and ecosystem function Chapter 13

Plant diversity and ecosystem function

Chapter 13

Why do we care about biodiversity?

Chapin III et al. 2000

How does biodiversity affect ecosystem function (or vice versa)?

Regional species pool

Local community

structure

Biotic factors

Evolutionary processes

Physiological constraints

Historical events

Dispersalabilities

Habitatselection

From Morin (2011)

Abiotic factors

Interspecific competitionHerbivoryFacilitation, mutualism

Ecosystem function

• Productivity• Nutrient retention• Soil CO2 flux

Diversity

• Alpha: # species at the local scale

• Beta (β): Difference between communities, species turnover

• Gamma (γ): # species at regional scale γ = β x α

VS.

HIGHLOW

VS.

α:

β:

Whittaker 1960

How many species can be lost before ecosystem function is impacted?

Loreau et al. 2001


• Tilman and Downing (1996)• Grassland in Minnesota• Looked at drought resistance of plant communities

with different levels of richness


• Naeem et al. (1994)

• 9, 15, and 31 species treatments – distributed among trophic levels

Ecotron, UK

Naeem et al. 1994

High diversity communities consumed more CO2 and were more productive (greater light interception)

Ways in which biodiversity can affect ecosystem function

• Productivity - how much carbon is assimilated

• Stability - how much productivity fluctuates under different environmental conditions

• Invasibility - indirectly affects ecosystem processes

Biodiversity and Productivity

• Scale dependant• Potential Mechanisms

– Productivity and size correlate (Oksanen 1996)

– Resource / energy constraints (Preston 1962, Wright et al. 1993)

– Competition and dominant species (Grime 1973)

– “Paradox of enrichment” (Rosenzweig 1971) – Reordering causes short term diversity losses

Biodiversity and Productivity - Neutral

Oksanen 1996 Journal of Ecology

Biodiversity and Productivity – “Paradox of enrichment”

• With fertilization, productivity is generally increased, but species richness declines

• Speculated to be due to changes in which species is dominating the system Stevens and Carson 1999


Div

ersi

ty (H

’)

Knapp et al. 2002


Found positive relationship between species richness and productivity in US and across Europe

Loreau et al. 2001

Biodiversity and Productivity – “It depends”

Adler et al. 2011

Biodiversity and Productivity - Scale

Mittelbach et al. 2001

On a regional scale, productivity and diversity were correlated in many more systems than at smaller scales


The number of functional groups were shown to be more important than species richness (in this study at least)

Hector et al. 1999

Biodiversity and Ecosystem Stability

• Dynamic stability – System returns to its “original” state after small perturbations– Robert May (1973) thought that increased

diversity would actually lead to decreased dynamic stability

– New theoretical models suggest that increased diversity will not increase dynamic stability but might not decrease it either.


• Stability - How much does a system differ from one year to the next (usually in terms of productivity)?– Coefficient of variation– Stability – signal to

noise ratio

Cv = σ/µ

Stability = µ /σ


Signal to noise ratio

Tilman et al. 2006

Coefficient of variation

Tilman et al. 1996

Biodiversity and Invasion

Kennedy et al. 2002

Biodiversity and Invasion• Native richness can be

positively correlated with exotic species richness

• Observational pattern– No causation

• Resource rich vs. resource poor

• Beta diversity

Stohlgren et al. 1999

Biodiversity and Invasion• Environmental heterogeneity can

influence invasion (Davies et al. 2005)

• Suggests beta diversity may be just as, if not more important in controlling exotic species

Photo credit: Koerner, S.

Biodiversity and Invasion

• Invasive species can then have drastic effects on ecosystems– Reductions in

biodiversity– Drastic changes to soil

nutrient cycling (Ehrenfeld 2003)

– Can change disturbance regimes (D’antonio and Vitousek 1992, Mack and D’antonio 1998)

Exercise 1

• Dependent variable: Aboveground biomass (productivity)• independant variable: Species richness• Come up with a hypothesisQuestions:1. Describe the relationship between the number of plant

species and plant biomass2. How does the relationship between biomass and species

richness change over time? 3. How does it stay the same?4. How do the error bars change the way you interpret these

results?

Fargione and Tilman 2004 Teaching Issues and Experiments in Ecology (TIEE)

Sampling effect hypothesis

• With random assembly:– Higher diversity results

in a higher chance that there will exist a dominant species in the community, thus increasing productivity.

Loreau et al. 2001

Exercise 2

• Dependant variable: % plots exceeding biomass of the monoculture plots

• Independent variable: Species richness• Articulate hypothesis (Sampling effect)1. Do the data support or reject the hypothesis? Does

the answer depend on the year?2. Why might a diverse plot contain more biomass

than even the highest monoculture plot? Why might two species be better than one when it comes to biomass production?

Fargione and Tilman 2004 Teaching Issues and Experiments in Ecology (TIEE)

References• Adler, P. B., E. W. Seabloom, E. T. Borer, H. Hillebrand, Y. Hautier, A. Hector, W. S. Harpole, L. R. O’Halloran, J. B. Grace, T. M. Anderson, and others.

2011. Productivity is a poor predictor of plant species richness. science 333:1750–1753.

• Chapin III, F. S., E. S. Zavaleta, V. T. Eviner, R. L. Naylor, P. M. Vitousek, H. L. Reynolds, D. U. Hooper, S. Lavorel, O. E. Sala, S. E. Hobbie, and others. 2000. Consequences of changing biodiversity. Nature 405:234–242.

• D’Antonio, C. M., and P. M. Vitousek. 1992. Biological invasions by exotic grasses, the grass/fire cycle, and global change. Annual review of ecology and systematics 23:63–87.

• Davies, K. F., P. Chesson, S. Harrison, B. D. Inouye, B. A. Melbourne, and K. J. Rice. 2005. Spatial heterogeneity explains the scale dependence of the native-exotic diversity relationship. Ecology 86:1602–1610.

• Ehrenfeld, J. G. 2003. Effects of exotic plant invasions on soil nutrient cycling processes. Ecosystems 6:503–523.

• Grime, J. P. 1973. Competitive exclusion in herbaceous vegetation. Nature 242:344–347.

• Hector, A., B. Schmid, C. Beierkuhnlein, M. Caldeira, M. Diemer, P. Dimitrakopoulos, J. Finn, H. Freitas, P. Giller, J. Good, and others. 1999. Plant diversity and productivity experiments in European grasslands. Science 286:1123–1127.

• Kennedy, T. A., S. Naeem, K. M. Howe, J. M. Knops, D. Tilman, and P. Reich. 2002. Biodiversity as a barrier to ecological invasion. Nature 417:636–638.

• Knapp, A. K., P. A. Fay, J. M. Blair, S. L. Collins, M. D. Smith, J. D. Carlisle, C. W. Harper, B. T. Danner, M. S. Lett, and J. K. McCarron. 2002. Rainfall variability, carbon cycling, and plant species diversity in a mesic grassland. Science 298:2202–2205.

• Loreau, M., S. Naeem, P. Inchausti, J. Bengtsson, J. Grime, A. Hector, D. Hooper, M. Huston, D. Raffaelli, B. Schmid, and others. 2001. Biodiversity and ecosystem functioning: current knowledge and future challenges. science 294:804–808.

• Mack, M. C., and C. M. D’Antonio. 1998. Impacts of biological invasions on disturbance regimes. Trends in Ecology \& Evolution 13:195–198.

References• May, R. M. 1973. Time-delay versus stability in population models with two and three trophic levels. Ecology:315–325.

• Mittelbach, G. G., C. F. Steiner, S. M. Scheiner, K. L. Gross, H. L. Reynolds, R. B. Waide, M. R. Willig, S. I. Dodson, and L. Gough. 2001. What is the observed relationship between species richness and productivity? Ecology 82:2381–2396.

• Naeem, S., L. J. Thompson, S. P. Lawler, and J. H. Lawton. 1994. Declining biodiversity can alter the performance of ecosystems. Nature 368:21.

• Oksanen, J. 1996. Is the humped relationship between species richness and biomass an artefact due to plot size? Journal of Ecology 84:293–295.

• Preston, F. W. 1962. The canonical distribution of commonness and rarity: Part I. Ecology 43:185–215.

• Rosenzweig, M. L., and others. 1971. Paradox of enrichment: destabilization of exploitation ecosystems in ecological time. Science 171:385–387.

• Stevens, M. H. H., and W. P. Carson. 1999. Plant density determines species richness along an experimental fertility gradient. Ecology 80:455–465.

• Stohlgren, T. J., D. Binkley, G. W. Chong, M. A. Kalkhan, L. D. Schell, K. A. Bull, Y. Otsuki, G. Newman, M. Bashkin, and Y. Son. 1999. Exotic plant species invade hot spots of native plant diversity. Ecological Monographs 69:25–46.

• Tilman, D., and J. A. Downing. 1996. Biodiversity and stability in grasslands. Ecosystem management: selected readings 367:363–365.

• Tilman, D., P. B. Reich, and J. M. Knops. 2006. Biodiversity and ecosystem stability in a decade-long grassland experiment. Nature 441:629–632.

• Whittaker, R. H. 1960. Vegetation of the Siskiyou mountains, Oregon and California. Ecological Monographs 30:279–338.

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Plant diversity and ecosystem function Chapter 13