Intermediate Disturbance Hypothesis

​Intermediate Disturbance Hypothesis

​The intermediate disturbance hypothesis (IDH) states that moderate levels of disturbance lead to greater species diversity than lower or higher levels of disturbance.

Multiple Choice

How the makeup of a community changes over time starting from the day after a disturbance.

• ecological succession

• change

• high biodiversity

• soils

Multiple Choice

This is when organisms populate an area for the first time.

• high biodiversity

• primary succession

• low biodiversity

• change succession

Multiple Choice

This community contains a predictable assemblage of species that would remain stable until the next big disturbance.

• populate community

• climax community

• lycophytes community

• dense forests

Multiple Choice

We now know that an ecosystem is in later successional stages if it has...

• high biodiversity

• species

• populate

• change

Multiple Choice

What is a change brought about by a physical, chemical, or biological agent that impacts population size or community structure?

• resistance

• stability

• disturbance

• resilience

Multiple Select

Which of the following are examples of natural disturbances? (Select ALL that apply!)

• tornado

• tsunami

• volcano

• earthquake

• urbanization

Multiple Choice

Higher biodiversity =

• higher ecosystem resilience

• lower ecosystem resilience

Multiple Choice

What is habitat diversity?

• Diversity within a species

• # of species and abundance in the community

• How many different habitats are in a region

Multiple Choice

What is species diversity?

• Diversity within a species

• # of species and abundance in the community

• How many different habitats are in a region

• ​IF an ecosystem suffers frequent disturbances, many of the ecological relationships are disrupted and organisms may find it difficult to survive & reproduce. Some species die out.

• IF an ecosystem is rarely disturbed, then it is stable and the number of species remains relatively unchanged.

• Intermediate levels of disturbance may actually stimulate microevolution and speciation!

Multiple Choice

This hypothesis says that intermediate disturbances—not too big and not too little—are ideal.

• build or rebuild soils

• Long Disturbance Hypothesis

• Intermediate Disturbance Hypothesis

• Small Disturbance Hypothesis

​How can IDH stimulate Microevolution?

​The IDH proposes that species diversity is generally maximized if disturbance is neither too rare nor too frequent because species that thrive at both early and late successional stages can coexist.

Multiple Choice

The only constant is...

• death

• change

• taxes

• birth

Multiple Choice

What is the ability of an ecosystem to recover after it has undergone a disturbance?

• resistance

• stability

• disturbance

• resilience

​On a larger scale, disturbances of intermediate frequency and/or intensity may generate diversity. For example, a fire of intermediate or mixed severity could increase diversity by generating spatial heterogeneity within a landscape.

This is because a mixed severity fire will result in a complex of patches in a landscape. Patches differ in severity of burn and include:
- unburned patches
- low severity burn patches
- moderate severity burn patches where perhaps one-third to two-thirds of the vegetation is killed
- high severity burn patches where almost all the vegetation is killed .

In this case, the IDH may not hold on a local scale (within patches) because species richness within a small area may decline (for example, in severely burnt areas). However, on a larger landscape scale a fire of intermediate severity may increase species diversity. This is because areas or patches that differ in burn severity, and that are at different stages of post-fire change, would sustain more species with different disturbance sensitivities.

​spatial heterogeneity - the uneven distribution of characteristics or features across a landscape or population.