What are the causes and consequences of variation in diversity

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What are the causes and consequences of variation
in diversity?
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What are the causes and consequences of variation
in diversity?
How is diversity related to temporal variability?
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History of ideas on diversity and stability

• Wild speculation-
• Elton 1958
• MacArthur 1955

Stability increases as the number of links
increases. If the number of prey species for
each species remains constant, an increase in the
number of species in the community will increase
the stability. -MacArthur 1955
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History of ideas

• Math defies intuition-
• May 1973
• Gardner and Ashby 1970

More species greater chance of including
unstable combinations of strong interactions -gt
extinctions and fluctuations if interaction
strength is uniformly distributed
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History of ideas

• The role of interaction strength
• Yodzis 1981
• McCann et al. 1998
• Berlow 1999

Early data unequivocally indicate that
distributions of interaction strength are
strongly skewed toward weak interactions. It
seems, then, that weak interactions may be the
glue that binds natural communities
together -McCann et al. 1998 Nature
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History of ideas

• Wild speculation-
• Math defies intuition-
• The role of interaction strength-

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How are diversity and stability related in nature?
What can species-time relations tell us about
diversity and stability?
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Questions?

• How do diversity and stability covary in lake
  zooplankton assemblages?
• How is diversity related to environmental
  variability?
• Does regional diversity stabilize ecosystems?
• Patrick Thompsons M.Sc. thesis

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How do we measure stability?Species turnover
a daily richness z turnover ST long-term
richness
ST aTz
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A simple modelShurin 2007 Oikos

• Species blink in and out
• Diversity affects invasion and extinction
• invasion resistance
• facilitation
• Environmental variation affects invasion and
  extinction
• storage effects, variability enhances coexistence
• stochastic extinction, variability prevents
  coexistence

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And the data say
Toolik
SE AK
ELA
Quebec
Kodiak
Dorsett
Lake Geneva
Washington
Wisconsin
36 lakes 483 lake-years 5,364 samples
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Daily, annual and inter-annual richness
Shurin et al. 2007 Ecology Letters 10 127
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Richness and turnover
Shurin et al. 2007 Ecology Letters 10 127
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Richness and turnover
Shurin et al. 2007 Ecology Letters 10 127
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Richness and turnover
Shurin et al. 2007 Ecology Letters 10 127
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Conclusions

• Feedbacks among diversity, invasion, extinction
  and the environment influence different aspects
  of species-time
• Zooplankton show scale-dependent patterns
• positive correlations within the temperate zone
• negative correlations across latitudes

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Environmental stability and diversity-a double
edged sword

• Abiotic variability can either increase or
  decrease coexistence
• Storage effects vs. geometric mean fitness

What is the net effect of environmental variation
on diversity?
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How to measure environmental variability
Clearwater Lake, Ontario
date
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The data set
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The data set
surface temperature bottom temperature chlorophyll
a total nitrogen total phosphorus maximum
O2 minimum O2 conductivity pH DOC zooplankton
species
X 10 variables
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The data set
X 53 lakes
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The data set
X 53 lakes
1,042 years
5,932 monthly samples
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How do we partition environmental variability
among time scales?

• Multiplicative model of variance decomposition
• Xt XltAtStEt
• Xlt long-term mean
• At inter-annual component (XA/Xlt)
• St seasonal component (XM/XA)
• Et residual or unpredictable component

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How do we partition environmental variability
among time scales?

• Multiplicative model of variance decomposition
• Xt XltAtStEt
• Xlt long-term mean
• At inter-annual component (XA/Xlt)
• St seasonal component (XM/XA)
• Et residual or unpredictable component

Standard Deviation measures variance on each
time scale

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The interannual component
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The interannual component as deviation from the
long-term mean
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deviation from the mean
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Conductivity has high interannual variation
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Total nitrogen has low seasonal variation
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Temperature has high seasonal variation
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Low and high variability lakes- pH
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Low and high variability lakes- pH
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Low and high variability lakes- temperature
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Low and high variability lakes- temperature
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How does variability relate to zooplankton
diversity?

• Long-term mean
• Interannual variability
• Seasonal variability
• Residual (unpredictable) variability

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Zooplankton species richness and mean
environmental conditions
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Zooplankton species richness and interannual
variability
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Zooplankton species richness and seasonal
variability
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Zooplankton species richness and residual
variability
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Interannual and residual variation are better
predictors of diversityaverage conditions and
seasonality- not so much
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Conclusions

• Diversity mostly increases with greater thermal
  variability but declines with chemical
  instability
• Environmental variability (especially interannual
  and unpredictable) are more important for
  diversity than average conditions

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Increasing frequency of extreme
variationEasterling et al. 2000 Science
birth of Jon
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How does diversity affect ecosystem resilience?
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How does diversity affect ecosystem resilience?

• Local diversity affects stability, but who cares?
• Regional diversity may matter in a changing
  environment
• Pool of diverse traits for any occasion

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Experimental design

• 2 x 2 x 2 factorial
• warming (2.5 ºC)
• salinity (3 ppt)
• dispersal of regional zooplankton species

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Interactive effects of warming and dispersal on
zooplankton composition
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Interactive effects of warming and dispersal on
ecosystem processes
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No interactive effects of salinity and dispersal
on ecosystem processes
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Why regional diversity was more important in the
warming treatment
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Conclusions

• Dispersal and regional diversity can stabilize
  some ecosystem functions
• limited capacity
• only some stresses (warming, not salt)
• only some functions (production)
• Regional diversity in response to warming greater
  than to salinity

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Its like that cuz I says so
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Thanks

• Helmut Hillebrand
• Monika Winder
• Rita Adrian
• Bill Keller
• Blake Matthews
• Andrew Paterson
• Michael Paterson
• Bernadette Pinel-Alloul
• Jim Rusak
• Shelley Arnott
• Allyson Longmuir
• Norm Yan
• Patrick Thompson

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Thanks
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