Transcript PowerPoint Presentation on Ecosystems

Macroecological questions.
•
•
•
•
What patterns exist, and how are they
determined by environment vs. history?
How are ecosystems structured, and how is this
structure shaped by evolution?
What is the relationship between structure and
function?
What are the robustness and resilience
properties of ecosystems and how are they
shaped by evolution?
HOT features of ecosystems
• Organisms are constantly challenged by environmental
uncertainties,
• And have evolved a diversity of mechanisms to minimize
the consequences by exploiting the regularities in the
uncertainty.
• The resulting specialization, modularity, structure, and
redundancy leads to high densities and high throughputs,
• But increased sensitivity to novel
perturbations not included in
evolutionary history.
• Robust, yet fragile!
• Complex engineering systems are
similar.
Uncertainty
and
Robustness
Complexity
Interconnection/
Feedback
Dynamics
Hierarchical/
Multiscale
Heterogeneous
Nonlinearity
Uncertainty
and
Robustness
Complexity
Interconnection/
Feedback
Dynamics
Hierarchical/
Multiscale
Heterogeneous
Nonlinearity
Turbulent
Shear flows
coupling
Tight
Telephone
system
Organisms
Power
grid
Ecosystems
Internet
Post
office
Loose
Ideal
gas
Homogeneous
Socioeconomic
systems
Heterogeneous
Turbulent
Shear flows
coupling
Tight
Telephone
system
Organisms
Power
grid
Ecosystems
Internet
Post
office
Loose
Ideal
gas
Homogeneous
Socioeconomic
systems
Heterogeneous
Turbulent
Shear flows
coupling
Tight
Telephone
system
Organisms
Power
grid
Ecosystems
Internet
Post
office
Loose
Ideal
gas
Homogeneous
Socioeconomic
systems
Heterogeneous
Organisms
Telephone
system
Internet
design
All
Turbulent
Shear flows
None
Phase transitions
Ideal gas
“Complexity”
Ecosystems
Control
Theory
Computational
Information
Theory
All
design
Theory of
Complex systems?
Complexity
None
Statistical
Physics
Dynamical
Systems
1
dimension

Universal network behavior?
throughput
Congestion
induced
“phase
transition.”
Similar for:
• Power grid?
• Freeway traffic?
• Gene regulation?
• Ecosystems?
• Finance?
demand
Networks
log(thru-put)
Making a “random network:”
• Remove protocols
– No IP routing
– No TCP congestion control
• Broadcast everything
 Many orders of magnitude
slower
random
networks
Broadcast
Network
log(demand)
Networks
real
networks
log(thru-put)
HOT
random
networks
Broadcast
Network
log(demand)
The yield/density curve
predicted using random
ensembles is way off.
designed
Yield,
flow, …
HOT
random
Densities, pressure,…
Similar for:
• Power grid
• Freeway traffic
• Gene regulation
• Ecosystems
• Finance?
Turbulence
streamlined
pipes
Log(flow)
HOT
random
pipes
log(pressure drop)
Ecosystems?
“throughput?”
real food
webs
HOT
random
food webs
“density?”
“throughput?”
• reproduction
• carbon
• biomass
real food
webs
HOT
random
food webs
May: generic complexity
destabilizes models
but
ecosystems are not random
collections of organisms
“density?”
• Genes
• Cells
• Neurons
• Organisms
HOT features of ecosystems
• Organisms are constantly challenged by
environmental uncertainties,
• And have evolved a diversity of mechanisms to
minimize the consequences by exploiting the
regularities in the uncertainty.
• The resulting specialization, modularity, structure,
and redundancy leads to high densities and high
throughputs,
• But increased sensitivity to
novel perturbations not included
in evolutionary history.
• Robust, yet fragile!
Ecosystems and extinction
Observations
• 99.9% of all species which have ever existed are
now extinct
• Extinction events have heavy tails.
• 5 major extinction events and numerous smaller
ones.
• Currently in the sixth major extinction with the
rate increasing orders of magnitude in the last
10,000 years.
Ecosystems and extinction
• There is an ongoing debate about the cause of these
extinctions.
• Biologists generally agree that they are due to
catastrophic external events
– meteor impacts
– large scale geophysical phenomena.
• Advocates of SOC/EOC argue instead that they are due
to SOC/EOC “co-evolutionary biological phenomena.”
• But while extinctions may be triggered by exogenous
events, the distribution of extinctions for a given
disturbance is a fairly structured, deterministic, and
even predictable process.
Habitats
terrestrial
island
tropical
vs.
vs.
vs
marine
continental
nontropical
greater extinction vulnerability
Specialization
• Within a habitat, specialization offers short-term
benefits.
• Evolution necessarily ignores events that don’t actually
happen, even if they are catastrophic. (So do we.)
• Thus tails may be extra heavy.
• Specialization consistently correlates with extinction risk
in large extinctions.
• For example, body size increases over time on average
(both within and across species).
Specialization
• Large body size has been a risk factor in all major
extinctions (although not always in marine animals).
• However, in the smaller late Eocene extinctions, largebodied mammal species were not selected against.
• This highlights the role of external causes and the highly
structured form of the response, because...
• The late Eocene extinctions were generally related to
global cooling, which tends to favor large body size.
Evolution and extinction
“throughput?”
HOT
Specialization
Disturbance
“density?”
Ecosystems and extinction
• There is an ongoing debate about the cause of the large
extinctions that are known from the fossil record.
• Biologists generally agree that they are due to
catastrophic external events
– meteor impacts
– large scale geophysical phenomena.
• Advocates of SOC/EOC argue instead that they are due
to SOC/EOC “co-evolutionary biological phenomena.”
• But while extinctions may be triggered by exogenous
events, the distribution of extinctions for a given
disturbance is a fairly structured, deterministic, and
even predictable process.
What’s at stake?
If ecosystems are:
• EOC/SOC: Specie extinction, global warming,
etc. are random fluctuations. Not to worry,
nothing to do. Details don’t matter.
• HOT: Robust, but fragile. Details do matter.
HOT
SOC/EOC