1. Thinking Systems Class 10 Matt Cohen, PhD

2. A Rat Infestation Gainesville home built in 1928 –No rats when we moved in Lived there for just under 2 years –“Massive” control efforts by the end Owners of 2 large dogs –Exceedingly poor hunters Neighborhood of cat owners –Every direction (E, W, N, S) had one or more felines –Drove the dogs crazy…ever- vigilant border patrols + - -

3. Elements of Systems Boundary (the yard, canine patrolled) Inputs and outputs (cats, dead rats) Internal components (rats, dogs, cats) Interactions –Positive interactions (rats breeding) –Negative interactions (cats on rats, dogs on cats)

4. Why Systems? Interactions create complexity –Emergent behavior Water is “wet” Traffic snarls (even without accidents) The Rise of Fall of Pet Rocks Thresholds (tipping points) exist –Predicting these is enormously important Global climate change, business cycles, disease epidemics Epileptic seizures, landslides, fisheries collapse Systems aren’t more complex than we think, they are more complex than we can think. –But…we have to try! $3.95 each (!)

5. Key Attributes of Systems I. Mutual causality –Components affect each other, obscuring linear cause-effect Popularity → sales → popularity Poverty → soil erosion → poverty Chicken → Egg → Chicken Indirect effects –Component A exerts control over Component B via its action on Component C AB AB C

6. Indirect Effects - Aleutian Islands Nutrients are essential for plant and animal production –Phosphorus (P) is often limiting nutrient Essential for ribosomes and metabolism Limited geologic source in the region Amount of P controls the productivity of the ecosystem Grassland production of Aleutian islands is P limited Sea bird guano is a rich P source –Was mined for fertilizer for years Abundant P Depleted P Croll et al. (2005) - Science

7. Nutrients and Sea Birds Seabirds eat fish from the sea but poop on land Major flow of P from sea to land that supports productive grasslands Marine Birds Grassland Production Fish Soil P + + +

8. Predator Control of Ecosystems Introduce Arctic Foxes –Top-predator –Seabirds never had a terrestrial predator –Decimated the sea-bird populations Marine Birds Grassland Production Fish Soil P + + + Arctic Foxes - Roughly 300% more soil P AND biomass on fox-free islands than on fox-infested islands

9. Key Attributes of Systems II. Consist of processes at different space/time scales –Fast and slow variables Humans and viruses Evolution and extinction Supply and demand Systems are historically contingent –Deep dependence on what happened in the past The Great Unfolding Beta-max, Bacteria, Base 10 AB A B C

10. Fast and Slow: Beer and the Business Cycle There exists a cycle of boom (bull) and bust (bear) periods in economic systems…WHY?

11. A Systems View of Boom and Bust 1.The structure of a system influences behavior. Systems cause their own problems, not external forces or individual errors. –Distribution chains (and economies) contain fast and slow moving parts –Communication between parts is LAGGED 2. Human systems include the way in which people make decisions. 3. People tend to focus on local optimization NOT global optimization.

12. Consider a Typical Supply Chain Retailer: Sells products, varying consumer demand, orders to wholesalers for next weeks delivery Wholesalers/Distributors: Distribute beer to multiple retailers, orders to brewery for two weeks in the future Brewery: Make beer, adjust production to demand ALL –Avoid the costs of excess and insufficient inventory J. Sterman at MIT http://web.mit.edu/jsterman/www/SDG/beergame.htmlhttp://web.mit.edu/jsterman/www/SDG/beergame.html

13. Beer Game Simulator Brewery Wholesaler Distributor Retailer Team 1 Team 2 Team 3 Team 4 ORDERS EXCESS/ BACKLOG Oscillation Amplification Lag Changing Demand

14. Dependence on History: Algae, Nutrients, and Shallow Lakes Shallow lakes (< 10 m deep) Two alternative “states” –Rooted vegetation (macrophytes) –Algae Shifts between the two occur catastrophically, and BOTH can occur under the same environmental conditions Where you are depends on where you’ve been

15. Self-Reinforcing Feedbacks in Shallow Lakes Rooted Plant State –Plants require clear water –Plants stabilize sediments –Stable sediments keep water P concentrations low AND limit stirring –Low P limits algae and high clarity favors rooted plants Algae State –Algae makes ooze –Ooze is easily stirred up, making the water turbid and recycling P –More P makes algae grow faster AND sediments looser via loss of plants Regime shifts due to combined effects: –Too much P (human pollution) –Disturbances (pollution affects vulnerability)

16. Environmental Change and Ecosystem “State” Shifts Typical Models of Nature Emerging Model of Many Complex Systems Scheffer et al. (2001) - Nature

17. Thinking for Managing Complex Systems The “state” of a system is controlled by external forces AND internal interactions Indirect effects lead to surprising behavior Fast and slow variables interact to create instability –Spatial variability (local vs. global variable) also Managing for ONE THING often creates bigger problems later (discussion section)

18. The End Matt Cohen mjc@ufl.edu