Systems Approach. Ecosystem Community Population.

Systems Approach

Ecosystem

Community

Population

Ecosystem

Landscape

Community-Populations of different speciesthat interact.

Ecosystem

- the various communities of organismsinteracting with the environment.

Landscape -a physical area such as a watershedconsisting of various landscape elements(fields, forests) and the species found.

Community

• Species richness

• Species diversity

• Functional groups

• Life Forms

• Trend Analysis

• Statistical Approach

Ecosystem

• Energy Flow

• Nutrient cycling

Landscape

• Spatial Arrangement of landscape elements or units.

Community

• Central Question:

How is a community structured and by what?

• Are there patterns in community structure?

• If so, what has caused this pattern

• Competition

• Predation

• Time

• Size of patches (islands)

Equilibrium

Non-equilibrium

Equilibrium

- focus on the mean

Non-equilibrium

- focus on the variation

Equilibrium Non-equilibrium

Mean Variation

Predictability Unpredictable

Competition

Island Biogeography Disturbance

Succession

Competition

• An equilibrium concept.

Data from Gause 1934

• Competition is often not an important structuring process in communities.

Species area relationship

• Preston (1948, 1960 and 1962)

– S = CAz

– log S = (log C) + z(log A)

Island Biogeography

• 2 processes - extinction and colonization

• Function of – island size and distance frommainland.

Succession

-fire, insect damage, wind, flooding

-unpredictable in space and time

-results in non-equilibrium dynamics

-recognized as being central to ecosystems

Disturbance a non-equilibrium concept

Modeling Disturbance

Intermediate Disturbance Hypothesis

Predator Mediated Co-existence Hyp.

Effect of grazing on species richness

Succession

In the

Boreal Forest

Holling’s Four-Box Model of ecosystem function.

Keystone Species

Other Keystone species:

- Beaver (create ponds)

- Elephants (Trees)

- Sea otter (Seaurchins)

Community structure

• Equilibrium and non-equilibrium

AND

Time.

Complexity Stability

Stability Complexity

Complexity Stability Debate

• Elton Complexity -> Stability• May 1970’s Modeling – Not so!

• Subsequently refuted (late 80’s & 90’s)• Yodzis - modeling

– Tillman – experiments– BUT we still did not understand the nature of

stability

Summary• Populations

– movement– Fragmentation– Spatially structured populations

• Communities– Dynamic equilibrium/non-equilibrium– Competition– Island Biogeography

• Protected areas - corridors

– Disturbance• Intermediate disturbance hypothesis• predator mediated co-existance

• Ecosystem stability