In 1926 Italian biologist Umberto D’Ancona noticed that the ratio of predators (sharks and rays) in the Adriatic Sea was much higher during World War I than before or after. Since he did not understand what could be the reason, he asked his mathematician and senator father-in-law Vito Volterra, who wrote up a couple of equations, and explained to him the phenomenon. This is how the Lotka-Volterra model was born, which is one of the basic models of ecology.
The explanation of the shark problem is the following. Predators and prey interact with each other. If there is more prey, it has a positive effect on predators, as more food becomes available. However, if there are more predators, it has a negative effect on prey, as more gets eaten. This interaction leads to an equilibrium ratio of the two. During the war, fishing stopped in the Adriatic, but before and after it also affected the equilibrium. Fishing reduced the number of prey which had a negative effect of predators, and it reduced the number of predators, which had a positive affect on prey. So fishing had a double negative effect on predators (they were fished, and also their food), but it had an ambivalent effect on prey (they were fished, but also their predators). In conclusion: the ratio of predators was not high during the war, but low in peacetime.
I read this story about 10 years ago in Karl Sigmund’s marvelous book Games of Life, and it is one of the main inspirations behind Zandagort. Although there is no fishing (and fish) in the game, the inclusion of the ecosystem and the relation between that and economy stems from here.
Anyway, if you want to play with the ecosystem in Zandagort, just try the newly fixed ecosimulator.