Disturbance Ecology

Question 1

What are patch dynamics models?

Answer 1

Spatial variation in the nature of the community
Movement between patches via dispersal of individuals
Periodic disturbances as an important feature of communities

Question 2

What is a disturbance?

Answer 2

A discrete event that disrupts an ecosystem or community; often removes organisms from a community and opens up space which can be colonised.

Major cause of long-term fluctuations in the structure and functioning of ecosystems.

Must be defined in terms of the normal range of environmental variation that an ecosystem experiences.

Question 3

What is perturbation?

Answer 3

Includes concept of disturbance but also includes changes that do not result in a change in plant biomass e.g. rising CO2 concentrations.

Question 4

What are some examples of natural disturbance?

Answer 4

Treefalls, fires, droughts, pathogens, herbivores, eruptions

Question 5

What are some examples of human-induced disturbance?

Answer 5

Deforestation, overgrazing, chemical pollution, mining

Question 6

What are the properties of disturbance events?

Answer 6

Type, severity, frequency, size, timing and intensity.

Question 7

What is primary succession?

Answer 7

Gradual establishment of biotic communities in an area where little or no life existed before; there is no pre-existing seed bank. E.g. newly formed islands or glacier retreat.

Question 8

What is secondary succession?

Answer 8

Gradual re-establishment of biotic communities in an area where one was previously present. There is a pre-existing seed bank. E.g. treefall gaps, old field succession, forest fires.

Question 9

How does succession occur in a treefall gap?

Answer 9

Light admitted to the forest floor change the physical conditions needed for seedling establishment and decomposition.

Changes are more intense in tropical forests.

Trade-off between growth in gaps and survival in shade for seedlings/saplings.

Disturbance specialists (light-demanding species) and shade tolerant species.

Question 10

Explain the Intermediate Disturbance Hypothesis (IDH)

Answer 10

Attempts to explain the number of species coexisting in a community.

Disturbances that disproportionately affect competitive dominants may also increase diversity.

Diversity is greatest at moderate disturbance frequencies/magnitudes.

At low levels, compensatory mechanisms (competition or predation) reduce species diversity via competitive exclusion.