Monday, September 7, 2009

Modifying Google's "Page Rank" algorithm to track ecosystems

Judith Burns in the BBC: Google's algorithm for ranking web pages can be adapted to determine which species are critical for sustaining ecosystems, say researchers. According to a paper in PLoS Computational Biology, "PageRank" can be applied to the study of food webs.

These are the complex networks of who eats whom in an ecosystem. The scientists say their version of PageRank could be a simple way of working out which extinctions would lead to ecosystem collapse. Every species is embedded in a complex network of relationships with others. So a single extinction can cascade into the loss of seemingly unrelated species.

Investigating when this might happen using more conventional methods is complicated as even in simple ecosystems, the number of combinations exceeds the number of atoms in the universe. So it would be impossible to try them all.

Co-author Dr Stefano Allesina realised he could apply PageRank to the problem when he stumbled across an article in a journal of applied mathematics describing the Google algorithm. The researchers say they had to make minor changes to it to adapt it for ecology. Dr Allesina, of the University of Chicago's department of ecology and Evolution, told BBC News: "First of all we had to reverse the definition of the algorithm. "In PageRank, a web page is important if important pages point to it. In our approach a species is important if it points to important species."….

"Garden of Earthly Delights," a 1500 painting by Hieronymous Bosch


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