Download File - Kevin Wilcox

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)?
Physiological
constraints
Evolutionary
processes
Regional
species pool
Abiotic
factors
Habitat
selection
Dispersal
abilities
Biotic factors
Interspecific competition
Herbivory
Facilitation, mutualism
From Morin (2011)
Local
community
structure
Historical
events
Ecosystem function
• Productivity
• Nutrient retention
• Soil CO2 flux
Diversity
HIGH
LOW
• Alpha: # species at
the local scale
• Beta (β): Difference
between
communities,
species turnover
• Gamma (γ): #
species at regional
scale
α:
VS.
β:
VS.
γ=βxα
Whittaker 1960
How many species can be lost before
ecosystem function is impacted?
Loreau et al. 2001
How many species can be lost before
ecosystem function is impacted?
• Tilman and Downing (1996)
• Grassland in Minnesota
• Looked at drought resistance of plant communities
with different levels of richness
How many species can be lost before
ecosystem function is impacted?
• Naeem et al. (1994)
Ecotron, UK
• 9, 15, and 31 species treatments – distributed among
trophic levels
High diversity communities consumed more
CO2 and were more productive (greater light
interception)
Naeem et al. 1994
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
Biodiversity and Productivity
Diversity (H’)
Knapp et al. 2002
Biodiversity and Productivity
Loreau et al. 2001
Found positive relationship between species richness
and productivity in US and across Europe
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
Biodiversity and Productivity
Hector et al. 1999
The number of functional groups were shown to be
more important than species richness (in this study
at least)
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.
Biodiversity and Ecosystem Stability
• 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
Biodiversity and Ecosystem Stability
Coefficient of variation
Tilman et al. 1996
Signal to noise ratio
Tilman et al. 2006
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 hypothesis
Questions:
1. Describe the relationship between the number of plant
species and plant biomass
2. 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.