Disturbance Ecology

Dr. Mark McGinleySpecial Topics in Ecology and

BiodiversityISB, UM 2010

How Many Books in the Library?

• How would you try to figure out how many books in the library?– Counting is the boring way– Are there other approaches we could use to

estimate the number of books

Is the Library Full?

• If the library is full then it is relatively easy to determine the number of books in the library.

If the library is full

– Need to know• Total length of book shelves• Mean width of book

# books = total length of book shelves/mean book width

What If The Library is Not Full?

• Then we need to know a different approach,– We need to know something about the rate at

which books are added and lost from the library

How Does This Relate To Ecology?

Different approaches to understanding causes of patterns of biodiversity- are communities full of species or are communities not full of species.

Equilibrium Approach

• If communities are full of species, then we can understand biodiversity by understanding the factors that limit the number of species in a community– Competition – If competition determines community structure

then the maximum number of species that can be found in a community is equal to the number of niches.

Non-equilibrium Approach

• Sometimes communities are not full because something stops competitive exclusion from occurring– Predation– Disturbance

Disturbance

• “Disturbance” is a word that has a particular meaning in regular usage

– Typically a “disturbance” is something that disrupts “normal”

• Yelling and screaming in the library• Being told to “shush” at a football game

Disturbance

• Ecologically, disturbance has been defined in different ways by different people.– Important to recognize this and always be

aware of which definition people are using

Disturbance

• Pickett and White– A disturbance is any relatively discrete event

in time that disrupts population, community, and ecosystem structure

Fire

Fire

Landslides

Hurricanes

Hurricanes- Salt Water Damage

Tsunami

Floods

Not Disturbance-Drought

Disturbance

• Disturbances are regular and predictable events in many communities

Disturbance vs Disaster

• Disturbances occur frequently enough that natural selection can occur– Thus, many species are “adapted” to

disturbances

• Disasters occur so rarely natural selection has not occurred– Species are not adapted to disasters.

Disturbance Regime

• Frequency• Location• Magnitude• Intensity• Synergisms

Disturbance Regime- Fire

• Intensity– Crown fire vs. ground fire

Importance of Disturbance

• Evolutionary– Organisms should have adaptations that allow

them to survive or recover from disturbances

Serotinous Cones

Importance of Disturbance

• Ecological– Disturbance may effect species diversity in a

community– First person to think about this was Darwin

• He recognized more species of grasses growing in fields that had been moved for hay than in fields that were unmowed.

Competition Between Grasses

Connell’s Intermediate Disturbance Hypothesis