Trophic cascades: Wolves, bees and “spreadsheet thinking”
I don’t hate spreadsheets. Let me make that absolutely clear. I’ve used them for over 20 years and they are very useful. I’ve used them for all kinds of things from calculating inputs for air dispersion models to sizing relief valves and analysing my finances. I’ve even written a complete production reporting system in Excel and VBA for an onshore production facility.
However, I have also seen the dark side of spreadsheets; the misplaced confidence in our ability to model reality. I’m not the only one as there is a European Spreadsheet Risks Interest Group (EuSpRIG) and they have complied a list of over 80 public reports of spreadsheet errors (top 8 here).
What I want to explore here is two examples from nature that were not exactly caused by a spreadsheet but were caused by what I will call “spreadsheet thinking”. You know, build a model that represents your “problem” and “Solve for X” — manipulate the variables to maximise your favoured outcome.
Both of the examples below are instances of Trophic Cascades.
Trophic cascades are powerful indirect interactions that can control entire ecosystems
Both are examples of trying to optimise an outcome by using a model that is too simplistic.
Reintroducing wolves in Yellowstone National Park increased beaver numbers (link)
If you were a cattle rancher or livestock farmer in the early 1900’s you want to maximise the amount of meat you can sell (this is your X). Wolves (W) eat meat therefore driving W towards zero positively influences X. Simple right?
The last wolf was killed in 1926 (link) and sure enough it worked, at least it appeared to in the short term. Elk populations increased….
But they caused all sorts of other problems, including a reduction in the number of beavers because of the loss of willow trees lining the rivers. Coyote numbers shot up, so numbers of Coyote prey went down (rabbits etc.). It was anything but a targeted intervention and completely changed the ecosystem.
Wolves were reintroduced in 1995 and now there are 9 beaver colonies instead of just 1. Seems obvious now right, but at the time the cattle ranchers made a convincing argument and the government listened to their case and supported their wolf eradication.
However, as is so often the case, our model was too simple and the farmers were did not consider the secondary and tertiary effects in their thinking.
Industrialising farming reduces the number of bees and insects (link)
If you are an arable farmer then you want to maximise the yield from the land you have. This has typically been solved by:
- Removing hedgerows and making fields as big as possible so they can be worked easily by machines
- Using fertiliser to increase the growth rates of crops
- Using pesticides to kill all the things that eat your crops
Over the long term unexpected effects started to appear. Including increased soil erosion, the pollution of rivers and the decline in the bee populations (link). Now there are warnings that the decline in bees could wipe out the British apple industry (link).
Oops! The problem was, these interactions were not in the original model. The models only included part of the system — they were too simplistic and missed the complex interdependencies.
We can’t keep on making these catastrophic cock-ups. The next phase of growth will have to be more careful about its impact on the environment.