Intermediate Disturbance Hypothesis (IDH)

Ariane Ruby B. Sogo-anAdvanced Ecology

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.

“Are diverse communities more stable than species-

depauperate communities?”“Are stable systems more

diverse than unstable system?”

Factors that affects species diversity:

1. Invasive Species2. Keystone Species3. Availability of Resources4. Stability of Community

“How do say that an environment is stable or disturbed?”

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.

“Are diverse communities more stable than species-depauperate communities?”

“Are stable systems more diverse than unstable system?”

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.

• 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.

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

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.

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

Summary

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

END OF REPORT