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

RobustnessComplexity

Interconnection/FeedbackDynamics

Hierarchical/Multiscale

HeterogeneousNonlinearity

Uncertainty and

RobustnessComplexity

Interconnection/FeedbackDynamics

Hierarchical/Multiscale

HeterogeneousNonlinearity

Homogeneous Heterogeneous

Tight

Loose

coup

ling

Ideal gas

Internet

Post office

Turbulent Shear flows Power

grid

Organisms

Ecosystems

Telephone system

Socio-economic systems

Internet

Organisms

Ecosystems

Homogeneous Heterogeneous

Tight

Loose

coup

ling

Idealgas

Postoffice

TurbulentShear flows

HOTTelephone system

Power grid

Socio-economic systems

Internet

Organisms

Ecosystems

Homogeneous Heterogeneous

Tight

Loose

coup

ling

Idealgas

Postoffice

TurbulentShear flows

ComplexityTelephone

system

Power grid

Socio-economic systems

Internet

Organisms

Ecosystems

Idealgas

Postoffice

TurbulentShear flows

Socio-economicsystems

Complexity

Telephone system

Power grid

Internet

Organisms

Ecosystems

Ideal gas

TurbulentShear flows

“Complexity”

Telephone system

All

None

desi

gn

Phase transitions

HOT

1 dimension

All

None

desi

gnControl Theory

Statistical Physics

Dynamical Systems

Information TheoryComputational

Complexity

Theory ofComplex systems?

Universal network behavior?

demand

throughputCongestion

induced “phase

transition.”

Similar for:• Power grid?• Freeway traffic?• Gene regulation?• Ecosystems?• Finance?

random networks

log(thru-put)

log(demand)

Networks Making a “random network:”• Remove protocols

– No IP routing– No TCP congestion control

• Broadcast everything Many orders of magnitude

slower

BroadcastNetwork

Networks

random networks

real networks

HOTlog(thru-put)

log(demand)

BroadcastNetwork

random

designed

HOTYield,flow, …

Densities, pressure,…

The yield/density curve predicted using random ensembles is way off.

Similar for:• Power grid• Freeway traffic• Gene regulation• Ecosystems• Finance?

HOT

Turbulence

Log(flow)

log(pressure drop)

random pipes

streamlined pipes

Ecosystems?

random food webs

real food webs

HOT“through-

put?”

“density?”

random food webs

real food webs

HOT“throughput?”• reproduction• carbon• biomass

“density?”• Genes• Cells• Neurons• Organisms

May: generic complexity destabilizes models

butecosystems are not random

collections of 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

• 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.

Observations

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 vs. marineisland vs. continentaltropical vs

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, large-bodied 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.

HOT

Disturbance

Evolution and extinction

Specialization

“density?”

“through-put?”

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.

SOC/EOC

HOT

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.