A bit more complexity

Ok here’s another fascinating insight from Roger Lewin’s book Complexity.

Lewin reports on the work of Stuart Pimm and Jim Drake at the University of Tennessee who experimented with computer models of ecological communities. As I understand it, these models were based on fairly simple species of herbivores, carnivores and plants using basic rules about the space they need, what they eat/prey on etc. They added species one a time and watched how the ecosystem unfolded.

One thing they learnt was that species-rich communities resisted invasion by new predators more robustly than species-poor communities. And that mature species-rich communities were more robust than younger species-rich communities. All this using only a simplified computer model.

It gets more interesting. Drake found that

…if he started all over again with the same original pool of species, he again finished up with an extremely persistent community, but one of a different composition from the first. He ran it a third time, with the same result: a persistent community, different from the first two.

Drake got more excited by a second discovery which he described to Lewin:

Take one of these consistent communities with its say, fifteen species. Now reassemble the community from the beginning using only these same fifteen species, and you find you can’t do it, no matter what order or combination of orders of introduction you try. You simply cannot put the community back together again once you’ve taken it apart. I call it the Humpty Dumpty effect

I find it quite exciting that even in the relatively simple computer model success can’t be got by attempting to replicate what worked before. It seems as though we must always be willing to be open to something new if we are to create successful communities.

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