The web of life


Stories from a connected world – The web of life

Thousands of species disappear every year. The extinction of a species can affect many others, because the ecosystem has the structure of a network. Let’s look at an example.

In the early twentieth century, sea otters off the coast of California had almost disappeared because of hunting. In 1911, the U.S. government decided to protect them. Sea otters proliferated and fed abundantly on their main prey, sea urchins. The sea urchin population declined, which increased the amount of algae, their favourite food. With the renewed abundance of algae, more food became available for a range of fishes and coastal erosion was reduced. Avoiding extinction triggered a domino-effect.

Understanding ecosystems is not always easy. In the 1980s, the population of cod in the North Atlantic declined remarkably. Canadian stakeholders blamed seals, for being predators of cods. Although many seals were killed, the cod population continued to decline. In the late ’90s, ecologists drew the food chains that connect the seal and the cod, and obtained a dense and intricate picture [PDF], It was much more complex than it was supposed to be. An ecosystem is a network and, in order to understand it, one has to take into account the pattern of its connections.

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