What does it matter if the snail darter goes extinct, or the humpback chub, or an obscure beetle? This question has bedeviled conservationists and their critics for decades. Not long ago, Stefano Allesina, a computational ecologist at the University of Chicago, wondered whether he could use the power of Google to answer it — to calculate the relative significance of extinctions within an ecosystem.
Allesina borrowed Google’s PageRank algorithm and applied it to a food web — a model of what eats what in an ecosystem. In its intended role, PageRank determines a website’s relative importance in a user’s search by the importance of the sites that link to it. If, for example, the New York Times links to a page, that page is assumed to be important, and so…