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What are the causes and consequences of variation in diversity?. What are the causes and consequences of variation in diversity?. How is diversity related to temporal variability?. stability. diversity. History of ideas on diversity and stability. Wild speculation- Elton 1958
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What are the causes and consequences of variation in diversity?
What are the causes and consequences of variation in diversity? How is diversity related to temporal variability?
stability diversity 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
stability diversity History of ideas • Math defies intuition- • May 1973 • Gardner and Ashby 1970 More species = greater chance of including unstable combinations of strong interactions -> extinctions and fluctuations if interaction strength is uniformly distributed
stability diversity 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. 1998Nature
stability stability stability diversity diversity diversity History of ideas • Wild speculation- • Math defies intuition- • The role of interaction strength-
How are diversity and stability related in nature? What can species-time relations tell us about diversity and stability?
Questions? • How do diversity and stability covary in lake zooplankton assemblages? • How is diversity related to environmental variability? • Does regional diversity stabilize ecosystems? • Patrick Thompson’s M.Sc. thesis
35 30 Daily richness 25 20 10 20 30 40 50 60 70 80 90 100 50 45 Cumulative richness 40 10 20 30 40 50 60 70 80 90 100 Time How do we measure stability?Species turnover a = daily richness z = turnover ST= long-term richness ST = aTz
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
And the data say… Toolik SE AK ELA Quebec Kodiak Dorsett Lake Geneva Washington Wisconsin 36 lakes 483 lake-years 5,364 samples
Daily, annual and inter-annual richness Shurin et al. 2007 Ecology Letters 10: 127
Richness and turnover Shurin et al. 2007 Ecology Letters 10: 127
Richness and turnover Shurin et al. 2007 Ecology Letters 10: 127
Richness and turnover Shurin et al. 2007 Ecology Letters 10: 127
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
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?
How to measure environmental variability Clearwater Lake, Ontario date
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
surface temperature bottom temperature chlorophyll a total nitrogen total phosphorus maximum O2 minimum O2 conductivity pH DOC + zooplankton species X 10 variables The data set X 53 lakes
surface temperature bottom temperature chlorophyll a total nitrogen total phosphorus maximum O2 minimum O2 conductivity pH DOC + zooplankton species X 10 variables The data set X 53 lakes 1,042 years 5,932 monthly samples
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
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 }
The interannual component as deviation from the long-term mean
How does variability relate to zooplankton diversity? • Long-term mean • Interannual variability • Seasonal variability • Residual (unpredictable) variability
Zooplankton species richness and mean environmental conditions
Residual variability 16 16 14 14 12 12 zooplankton richness 10 10 8 8 6 6 4 4 0.0 0.1 0.2 0.3 0.4 0.5 -2.0 -1.5 -1.0 bottom temperature ln(TP) Zooplankton species richness and residual variability
Interannual and residual variation are better predictors of diversityaverage conditions and seasonality- not so much
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
Increasing frequency of extreme variationEasterling et al. 2000 Science birth of Jon
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
Experimental design • 2 x 2 x 2 factorial • warming (2.5 ºC) • salinity (3 ppt) • dispersal of regional zooplankton species
Interactive effects of warming and dispersal on zooplankton composition
Interactive effects of warming and dispersal on ecosystem processes
No interactive effects of salinity and dispersal on ecosystem processes
Why regional diversity was more important in the warming treatment