Google PageRank Could Help Keep Ecosystems Running

google pagerank meter photo

Image from dannysullivan

As it turns out, Google's search engine is good for more than just looking up your nearest library or favorite local grocery store -- try helping ecosystems run. According to Stefano Allesina of UCSB's National Center for Ecological Analysis and Synthesis, Google's PageRank algorithm can be used by ecologists to figure out which species are most crucial for an ecosystem to function, reports Nature's Emma Marris.

Allesina, who makes his living studying food webs, the networks that describe the feeding relationships within an ecosystem, says that determining what the consequences of removing one prey or another would be is one of the toughest aspects of his job.

starfish photo

Image from Dawn Endico
The "gold-standard" algorithm
The gold-standard method for dealing with what happens when a prey species is removed from the system is to use a genetic algorithm in which randomly generated possible solutions are assigned a greater or lesser degree of fitness. Fitter solutions are then combined to create a next-generation algorithm that benefits from their superior elements. The idea is to ultimately ‘evolve’ an optimal solution.

Google's results: "statistically indistinguishable"
Because running these algorithms is typically such a costly, lengthy chore, Allesina used PageRank to "rank" species according to how many predators wanted to eat them (PageRank works by assigning pages with a rank according to how many others link to it). He tweaked the formula a bit to make it work on his food web, and, after running it on his 18 data sets, found that the results were virtually indistinguishable from those obtained through the "gold standard" algorithm.

The algorithm produces a ranked list which determines which species would need to be removed to get what Allesina calls "maximum ecosystem meltdown". Allesina says it can be modified to include other factors, such as low birth rates and habitat loss, which would affect an ecosystem's resilience.

While it may strike some as being too mechanical or technical -- especially if it's to be used as part of a conservation plan -- the reality is that it's almost impossible to protect all vulnerable species in a faltering ecosystem. Saving those that play the most crucial roles, whether it's because they're important prey or predators (the so-called "keystone" species), would have the most beneficial impacts in preventing a complete meltdown. If anything else, it could be used as a last-ditch solution in case an ecosystem is poised on the brink of destruction.

Via ::Nature News: Google tool identifies linchpin species (news website)

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