Intermediate Disturbance Hypothesis (IDH)

1. Intermediate Disturbance
Hypothesis (IDH)
Ariane Ruby B. Sogo-an
Advanced Ecology

2. Learning Objectives:
1. Explain the link between Biodiversity and
Stability.
2. Determine the disturbance factors that
contributes to the variation of species in a
given area.
3. Explain the Intermediate Level of
Disturbance.

3. “Are diverse communities more stable
than species-depauperate
communities?”
“Are stable systems more diverse than
unstable system?”

4. Factors that affects species diversity:
1. Invasive Species
2. Keystone Species
3. Availability of
Resources
4. Stability of Community
“How do say that an environment is stable or
disturbed?”

5. What is disturbance in the aspect of
Ecology?
• Is a temporary change in average
environmental conditions that causes a
pronounced change in an ecosystem.
• Disturbances often act quickly and with great
effect, sometimes resulting in the removal of
large amounts of biomass.

6. “Are diverse communities more stable than
species-depauperate communities?”
“Are stable systems more diverse than unstable
system?”

7. Intermediate Level of Disturbance
Hypothesis (IDH)
• Joe Connel (1978), the highest local diversities
are actually maintained NOT in stable systems
but in communities of levels of disturbance.

8. • High level of Disturbance:
– Only good colonists (r-selected species) will
survive giving rise to low diversity.
• Low Level of Disturbance:
– Competitively dominant species will out compete
all other species and only a few k-selected species
will persist, yielding low diversity.
Most Diverse lies in between. Hence, Intermediate.

9. • Examples of communities with High species
diversity:
– Rain Forest (diversity maintained by storms)
– Coral Reefs (Diversity maintained by Hurricanes)

10. Seth Reice (1994)
• Disturbance operates in habitats of all types
and naturally disturbed areas are nearly
always more diverse than undisturbed areas.
• Many communities exist in nonequilibrium
state in which the species composition
changes.

11. Wayne Sousa (1979)
• Small boulder – 1.7 sessile plants/animal sp.
• Large Boulder – 2.5 sp.
• Intermediate Boulder – 3.7 mean sp k and r
sel.
~Rock Stability vs. Rock Size

12. Summary
• The most diverse communities are not
necessarily the stable. Rather, the most
diverse communities seem to exist at
intermediate level of disturbance.

13. END OF REPORT