Phylogenetic relationships between unicellular aquatic organisms

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Phylogenetic relationships between unicellular
aquatic organisms
purple sulfur bacteria, methanotrophs,
chemotrophic or autotrophic cant tolerate O2
Prokaryotic inorganic chemotrophs
cyanobacteria (tolerate O2, heterocysts)
heterotrophic bacteria eat organic resources,
predators or decomposers
endosymbiosis
Diversification of phytoplankton is largely
driven by evolution of new photosynthetic
pigments
eukaryotes
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Cyanobacteria- prokaryotes1350 described
species
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Why are cyanobacteria so famous?

• Evolved 2.5 bya, first to use water as a source
  of electrons in photosynthesis
• N-fixers, transformed global N cycle
• produced O2, transformed atmosphere into
  oxidizing environment
• ancestors of all eukaryotic life by endosymbiosis
  with bacteria
• gave rise to green algae 250mya
• now mostly known as a sign of pollution and for
  toxic compounds

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Chlorophytes- green algae6,000 species
Scenedesmus
Pediastrum
Volvox
Spirogyra
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Why are chlorophytes so famous?

• appeared 250mya
• have chloroplasts
• use chlorophyll-a and b
• have had their chloroplasts stolen by euglenids,
  among others
• evolved flagellae

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Euglenophytes1000 species
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Bacillariophyta- Diatoms200 general, 106
species
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Why are diatoms so famous?

• appeared 185mya
• the frustule (silicate petri dish)
• the auxospore (sexual stage)
• associated with silica availability

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Chrysophytes- golden brown500 species
Dinobryon
More species in fresh than salt water
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Cryptophytes100 species
Cryptomonas
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Pigments of phytoplankton

• All have chlorophyll-a
• phycobilin in cyanobacteria
• carotenoids in chrysophyta and bacillariophyta
• chl-a and chl-b in chlorophytes
• xanthophylls, mainly in cyanobacteria
• Pigments have different spectral properties, can
  be used to identify broad groups

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P and cyanobacteria (N-fixers)Smith 1983 Science
221669
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Distribution of lake phytoplankton taxa
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Sinking phytoplankton

• Stokes equation
• v 2gr2(?- ?)/9?
• ggravitational acceleration
• rradius (assuming sphere)
• ?fluid density
• ?algae density
• ?viscosity (stickiness)
• Adaptations to sinking
• density (gas vacuoles, e.g.)
• shape (dont be a sphere)
• size (r)

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What happens to phytoplankton?
Sinking (15-40 of PP)
Grazing by zooplankton (35-75 of PP)
affected by turbulent mixing cell size,
density, shape
adaptations for morphology (spines, mucous
coats) chemical defenses life history
adaptations colonial life history
adaptations for gas vacuoles flagella
(pyrophytes, cryptophytes)
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Fates of production in different systemsCebrian
1999 American Naturalist 154449
More production consumed by herbivores in aquatic
systems, more detritus accumulation on land
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Wind re-suspends sinking phytoplankton
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How do sinking losses change with productivity?
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What happens to phytoplankton that sink?

• Either lost to hypolimnion, aphotic zone
• Live as periphyton in littoral zone of lake

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How does periphyton production compare to
phytoplankton?Vadeboncoeur et al. 2003 Limnology
and Oceanography 481408
benthic of whole lake primary production
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Why is benthic productivity important?
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Benthic vs. fish prey for big fish
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Productivity from bottom to topVadeboncoeur et
al. 2002 Bioscience 52 44
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Effects of cell size

• competition
• SA/V
• grazing
• gape limitation of zooplankton
• sinking
• Stokes equation

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Things wed like to know about phytoplankton

• What determines their nutritional quality for
  herbivores?
• What determines their diversity?
• What determines their productivity?

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What determines nutritional quality of
phytoplankton for zooplankton?

• Elemental composition
• Biochemical composition
• Chemical defenses

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Effects of cell chemistryDeMott et al. 1998
Limnology and Oceanography 431147
Daphnia grows better on phytoplankton with lots
of P
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BUT lakes with lots of P have different
phytoplankton with less essential Fatty
AcidsMuller-Navarra et al. 2003 Nature 427 69
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What limits energy transfer from phytoplankton to
zooplankton?

• Food quantity (more zooplankton in eutrophic
  lakes) McCauley et al. 1988 Am Nat 132383
• Food quality
• Is it elements or molecules? P or fatty acids?

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What determines trophic efficiency?
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What determines trophic efficiency?Cebrian,
Shurin et al. 2008 PLoS ONE
Aquatic ecosystems
Terrestrial ecosystems
Not productivity (apparently)
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Nutrients!
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Things we know to affect trophic efficiency

• Total productivity
• goes down with productivity
• Loss of benthic productivity
• Low quality of algae in eutrophic lakes
• Algal quality
• mineral nutrients, N and P
• Essential Fatty Acids

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What controls phytoplankton diversity?

• Paradox of the plankton How can so many
  phytoplankton coexist if they all need the same
  things (light, C, N, P, etc.)?
• G.E. Hutchinson 1959 American Naturalist 93145
• Based on Gausses axiom of competitive exclusion

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Solutions to the paradox (and evidence for them)
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Solutions to the paradox 1 Multiple Resources

• Tilmans resource ratio hypothesis- Tilman 1981
  Ecology 62802
• Measured growth of 4 Diatom species on Si and P
• Predicted the outcome of competition- who wins?

Growth rate
Silicate
Phosphate
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The outcome of competition in lab experiments
Theory- based on monocultures
low SiP
high SiP
intermediate SiP
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Does this work in the real world?Interlandi and
Kilham 2001 Ecology 821270
Measured phytoplankton diversity and resource
availability (N, P, Si, light) over two years in
three lakes
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Phytoplankton diversity is highest in Yellowstone
Lakes when more resources are limitingInterlandi
and Kilham 2001 Ecology 821270
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Where do tradeoffs come from?Lichtman et al.
2007 Ecology Letters
mu maximum growth Q cell nutrient content m
mortality
Vmax maximum uptake R nutrient concentration
in the environment R nutrient
concentration where growth 0 K Half
saturation content
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How do these things affect R?
How are these traits related to each other?
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Tradeoffs between saturation, uptake and nutrient
demand
High minimum nutrient concentration (Qmin) -gt
fast growth rate
Fast growth -gt low R (no tradeoff)
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Has a lot to do with cell size
Big cells take up nutrients faster, but need more
nutrients for growth
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Lessons from correlations in functional traits

• Species that can take up nutrients quickly are
  more sensitive to low nutrients
• Big species can take up nutrients faster but
  dont do as well at low nutrients

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Can phytoplankton partition the light
spectrum?Stomp et al. 2004 Nature 432104
phycocyanin
Grew two cyanobacteria in white light (all
wave- lengths), or with only red or green
wavelengths
phycoerythrin
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More diverse phytoplankton communities capture
more light Streibel et al. 2009 American
Naturalist
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Lessons from resource competition theories

• tradeoffs can allow coexistence -gt promote
  diversity
• evidence for tradeoffs in multiple dimensions
• different nutrients
• different wavelengths of light
• growth vs. need for nutrients

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Solutions to the paradox 2Keystone predators

• Prevent competitive exclusion by eating dominant
  competitors
• Paine 1966 American Naturalist 10065
• Originally from intertidal zone- Sea stars eating
  mussels

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Keystone predators do they live in lakes?

• Grazers Tend to decrease diversity at low
  productivity and increase it at high productivity
• Worm et al. 2002 Nature 417 848

With Grazers
No Grazers
Sweden
Canada
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Zooplankton and phytoplankton diversitySommer et
al. 2001 Ecology Letters
Copepods eat big algae
Daphnia eat small algae
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Who says the world is in equilibrium?

• Gausses axiom says that species at equilibrium
  lt number of limiting resources
• Can have two kinds of non-equilibrium
• Extrinsic- Intermediate Disturbance Hypothesis,
  storage effects
• Intrinsic- Cycles and Competitive Chaos

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Extrinsic factors
Intermediate Disturbance Hypothesis
Storage Effects
Requires tradeoff in performance under
different sets of conditions
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Evidence for just such a tradeoff
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Intrinsic fluctuations non-equilibrium
population dynamicsHuisman and Weissing 1999
Nature 402 407
Competition for five resources can lead to
cycles, chaos, and coexistence of a potentially
unlimited number of species
5 species, 5 resources
12 species, 5 resources
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Does chaos happen in the real world?Beninca et
al. 2008 Nature 451 822
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Chaos in the real world? Zooplankton densities
in Blue Chalk Lake, Ontario
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Solutions to paradox of the plankton

• Multiple resources (resource ratio hypothesis)
• different nutrients
• different kinds of light
• life history tradeoffs
• Keystone predation (predators weaken competition)
• Non-equilibrium (extrinsic or intrinsic)

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Questions about phytoplankton

• What determines their diversity?
• What determines their abundance?
• What determines which kinds are more abundant?