The Wolves and Moose on Isle Royal

Isle Royale images from: http://www.kgcphoto.com/isle_royale_national_park.htm

Wolf and moose images from http://blog.kingsoutdoorworld.com/2007/02/

alright – back to work…

• Largest island in lake Superior• Isolated from mainland most of the time• Home to moose and wolves

For now: • concentrate on actions between wolves and

moose herd• ignore other influences on moose population

(such as ?)• rather limited “systems” approach

(see additional reading on web page)

How to describe feedback:

size of moose herd size of wolf pack

size of wolf pack size of moose herd

positive feedback

negative feedback

more food on four legs

more hungry mouths to feed

Example of a Feedback Loop

Size of moose herdMore food for wolves

Appetite for moose Size of wolf pack

Note:

A feedback loop needs to be closed !

Therefore it needs at least

• two components

• two connections between these components

Or Somewhat Simplified:

size of moose herd size of wolf pack

positive

negative

How to analyze a feedback loop:

• Need to disturb the system• Doesn’t matter where you start• Analyze how disturbance moves through

the system

• How does wolf – moose system behave ?

size of moose herd size of wolf pack

Sign of Feedback Loop

• number of negative couplings determines sign of feedback loop

• even number of negative couplings: positive feedback loop

• odd number of negative couplings: negative feedback loop

Effects of Negative of Positive Feedbacks

Effects of Negative of Positive Feedbacks• positive feedback: input signal will be

amplified

• negative feedback: input signal will be damped

Size of wolf and deer herds

From Science Times (3/19/1996) (http://www.admin.mtu.edu/urel/PressReleases/feature/wolves/wolf.html)