Recent collaborative projects in Jons life: baked, halfbaked and al dente

1
Recent collaborative projects in Jons
lifebaked, half-baked and al dente

• Baked How do predators affect ecosystem
  stability?
• Ben Halpern, Elizabeth Borer, Eric Seabloom
• Half-baked Does body size affect Beta diversity?
• Karl Cottenie, Helmut Hillebrand
• Al dente Does nutrient stoichiometry control
  diversity?
• Monika Winder, Helmut Hillebrand

2
Predator effects on ecosystem stabilityHalpern
et al. 2005, Ecology Letters

• Why are food chains short?
• Energetic efficiency constraints (Elton)
• Dynamic stability constraints (Pimm and Lawton
  1979, but see Sterner et al. 1997)
• Who cares?
• Humans affect food webs from the bottom
  (eutrophication) and top (predator removal or
  introduction)

3
Does the strength of trophic cascades vary among
ecosystems?

• Data from 102 experiments that
• manipulated primary predators
• measured herbivore, plant community biomass
• were done in six different ecosystems
• Effects of predators on mean and variance in
  plant and herbivore density

4
Meta-analysis of experiments in 6 systems
5
Bigger effects on herbivores than plants Shurin
et al. Ecology Letters 5785
6
Stability effects vary among systems Halpern et
al. Ecology Letters, in press.
7
Across systems, predators tend to destabilize
herbivore density have no effects on plant
stability
8
Mean and variance of effect size are unrelated
9
Conclusions

• Predators destabilize herbivore populations
• effects vary among systems
• Effects are buffered at plant trophic level
• Mean and variance decoupled

10
How does dispersal ability vary among aquatic
taxa?How does dispersal ability affect patterns
of diversity at different scales? with Karl
Cottenie and Helmut Hillebrand
11
Why would small organisms be better dispersers?

• Asexual reproduction,
• no Alee effect
• Large population size
• Dormant life history stages

Finlays Rule- ubiquity for organisms lt1-10mm,
endemism for ones gt10mm Science 2002 296
1061-1063
12
How should ß-diversity change with distance?
bad dispersers
Tilman, Lehman and Kareiva. 1997. Spatial Ecology
good dispersers
13
ß-diversity versus distance for different taxa
Data from 6681 lakes, 4629 streams Taxa include
phytoplankton, periphyton, zooplankton, insects,
mollusks, amphibians, birds and fish
14
Vertebrates show higher ß-diversity, clumpier
distributions
15
Two Explanations

• Vertebrates are worse dispersers than inverts
• Vertebrates respond to environmental variation at
  finer scales (why?)
• Implications for Finlays rule- suggests cutoff
  for dispersal limitation is bigger (between
  invertebrates and vertebrates)

16
Nutrient stoichiometry and species diversity
(Tilmans resource ratio hypothesis)With Monika
Winder and Helmut Hillebrand
Predicts maximum diversity at intermediate
resource ratios
17
Test 1 Four Yellowstone lakes (Interlandi and
Kilham 2001 Ecology 821270)
18
Test 1 Yellowstone lakes (Interlandi and Kilham)
19
Highest diversity when most resources limiting
20
Test 2 Grasslands (2 data sets) (Stan Harpole,
super-genius)
Sedgewick Reserve, Santa Ynez, CA
Park Grass Experiment (begun 1856), Silwood
Park, UK
Michael Jackson lives here
21
Sedgewick Reserve, Santa Ynez, CA
Park Grass Experiment (begun 1856), Silwood
Park, UK
22
Our data a global survey of nutrient ratios and
micro-algae diversity in lakes, streams,
oceansLake Erken, Sweden
23
Our data a global survey of nutrient ratios and
micro-algae diversity in lakes, streams,
oceansFinnish stream diatoms
Diatom diversity (Shannon)
TNTP
24
Our data a global survey of nutrient ratios and
micro-algae diversity in lakes, streams,
oceansLake Washington phytoplankton (1962-1999)