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Functional traits, trade-offs and community structure in phytoplankton and other microbes

Functional traits, trade-offs and community structure in phytoplankton and other microbes. Elena Litchman, Christopher Klausmeier and Kyle Edwards Michigan State University. NPZ. Z. P. I. N. Plankton Functional Groups. Z. P 2. P 4. P 1. P 3. I. N. Many Species. Z. P 1. P 1.

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Functional traits, trade-offs and community structure in phytoplankton and other microbes

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  1. Functional traits, trade-offs and community structure in phytoplankton and other microbes Elena Litchman, Christopher Klausmeier and Kyle Edwards Michigan State University

  2. NPZ Z P I N

  3. Plankton Functional Groups Z P2 P4 P1 P3 I N

  4. Many Species Z P1 P1 P1 P1 P1 P1 P28 P1 P1 P1 P1 P1 P1 P21 P1 P1 P1 P1 P1 P1 P14 P1 P2 P3 P4 P5 P6 P7 I N

  5. Continuum of Strategies Z I N

  6. Continuum of Strategies grazing resistant com- petitive light competitive nutrient competitive

  7. Trait-Based Approaches • Traits • Environmental gradients • Species interactions • Performance currencies (fitness measures) McGill et al. 2006 TREE

  8. Trait-Based Approach • Ecologically relevant traits • Trade-offs between these traits • Mechanistic models of population interactions • Fitness • Source of novel phenotypes

  9. Questions • What are key traits of (phyto)plankton? • What are the constraints on and trade-offs between traits? Can they be predicted from first principles? (How) can they be broken? • How are traits distributed along environmental gradients? Can traits explain species distributions? • How to link traits below (genomes, gene regulation, physiology) and above (community assembly evolutionary dynamics, phylogeny)?

  10. Ecologically relevant traits (phytoplankton) Litchman and Klausmeier 2008 Annual Rev. Ecol. Evol. Syst.

  11. Example: Nutrient Utilization TraitsBasic model (modified Droop)   growth Qmin Q V Vmax nutrient uptake K R Qmin Qmax Q • Traits: • µ∞, growth rate at infinite quota • Qmin, minimum internal nutrient content • Qmax, maximum internal nutrient content • Vmax, maximum uptake rate of nutrient • K, half-saturation constant for nutrient uptake

  12. Trait relationships

  13. Linking traits and community structure: Resource competition Species with the lowest minimum nutrient requirements to sustain growth, R* (Tilman 1982) • R* decreases (competitive ability increases) when • m∞ (growth at max Q) • Vmax(max uptake rate) • K (half-saturation constant) • Qmin (min quota) • m(mortality)

  14. What are the trade-offs between traits?

  15. Functional Group Distribution along a Trade-off CurveNiche differentiation? dinoflagellates diatoms coccolith greens Litchman et al. 2007 Ecol. Lett.

  16. Other measures of nutrient competitive ability Nutrient affinity

  17. Three-way trade-offs • Assembled trait information for all species we could find the data for • Considerable number of missing traits • Used statistical imputation techniques to infer missing trait values • Examined relationships between traits and competitive abilities for N and P

  18. Three-way trade-off Edwards et al. in press

  19. Three-way trade-off Edwards et al. in press

  20. Three-way trade-off Edwards et al. in press

  21. Light utilization traits vsgroup distribution in nature (US lakes)

  22. Using traits to explain species distributions English Channel phytoplankton time series

  23. Using traits to explain species distributions English Channel phytoplankton time series When N is low

  24. Traits in a Food Web Perspective Litchman et al. 2010

  25. Traits in a Food Web Perspective • Need to find ways to reduce dimensionality of traits that describe interactions between trophic levels • Use scaling relationships and stoichiometry to define traits

  26. Possible responses to changing environmental conditions • Phenotypic plasticity • Species/group replacements • Trait evolution, niche shifts • Combinations of the above

  27. Adaptive Dynamics Approach(a trait-based approach to evolutionary ecology) Eco-physiological traits & allometric relationships Abiotic factors Growth rate of invader vs resident (competition) ESS or other long-term evolutionary outcome (size)

  28. Marine vs Freshwater Diatom Cell Sizes Litchman et al. 2009 PNAS

  29. Diatom Size Evolution R Q B Vmax  K R × Qmin Q Qmin Qmax Q Litchman et al.2009 PNAS

  30. Allometries (power relationships) Freshwater Marine R2=0.76 R2=0.49 R2=0.61 R2=0.73

  31. ESS (N limitation) at different fluctuation periods, mixed layer depth and sinking Litchman et al.2009 PNAS

  32. Evolution Experiments 3. Assess trait distribution (mean and variance) before and after experiment under identical conditions Selection pressure Variance change Mean change or both! Single strain (mutation) Multiple strains (mutation or clonal selection)

  33. Evolution Experiments • Single species experiments (single or multiple strains) • Species in a community • Limits on trait evolution • Species replacement instead?

  34. Challenges and future directions • Still very few species with known traits • Significant gaps in trait coverage • With sparse trait data it is difficult to infer trade-offs, especially their shape • Need to characterize intraspecific variation and compare with interspecific differences—important for potential evolutionary changes

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