Lecture 4

Question 1

Resilience (engineering)

Answer 1

Capacity of a system to absorb disturbance and reorganize while undergoing change so as to still retain the same function, identity and feedbacks

Question 2

Resilience (ecosystem)

Answer 2

The capacity of an ecosystem to tolerate disturbance without collapsing into a qualitatively different state that is controlled by a different set of processes

Question 3

How is ecological resilience measured?

Answer 3

Magnitude of disturbance that can be absorbed before the system changes its structure by changing the variables and proceses that control behavior

Question 4

What is the result of resilience as a property of the system?

Answer 4

Persistence / Probability of extinction

Question 5

Stability

Answer 5

Ability of a system to return to an equilibrium state after a temporary disturbance

Question 6

What is the result of stability?

Answer 6

Degree of fluctuation around specific states

Question 7

Contrast: high resiliency/low stability vs. Low resilience/high stability

Answer 7

High resilience: wide distance between states
Low stability: ecosystem state is in a “shallow trough”, wide but low peaks between states.

Low resiliency: short distance between states
High stability: tall peaks/deep troughs surrounding an ecosystem state.

Question 8

In the absense of disturbance, what kinds of conditions can trigger an abrupt system response?

Answer 8

Gradually changing eg. nutrient loading, climate change, habitat fragmentation

Question 9

What happens when resilience is lost/decreased?

Answer 9

System is at high risk of shifting into a qualitatively different state (e.g. lake eutrophication)

Question 10

Compare and Contrast the resilience and stability viewpoints of system behavior

Answer 10

Resilience view: emphasizes domans of attraction and need for persistence (emphasis on heterogenity in viewing events in a regional instead of local context)
Stability view: emphasizes equilibrium, harvesting of nature’s excesses w/ minimal fluctuation (stable maximum subject to change)

Question 11

Intermediate disturbance hypothesis

Answer 11

Highest levels of diversity are supported at intermediate levels of disturbance (frequency or intensity)
Ex. Coral reefs and algal dominance- sea urchins conrolled algae; when they were wiped out by a pthogen, brown algae dominated reefs. this algae is unpalatable to remaining herbivores

Question 12

How can resilience be degraded?

Answer 12

1. Loss of biodiversity
2. toxic pollution
3. Unsustainable resource use (through industrial subsidies)
4. Climate change