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PageRank Algorithm Applied To the Food Web
An anonymous reader brings word of a new application for PageRank, Google's link analysis algorithm: monitoring the food web in an ecosystem. A team of researchers found that a modified version of PageRank can predict with great accuracy which species are vital to the existence of others. Quoting:
"Every species is embedded in a complex network of relationships with others. 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 realized he could apply PageRank to the problem when he stumbled across an article in a journal of applied mathematics describing the Google algorithm. '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.'"
Pagerank is just a repeated application of a transformation matrix. It has the effect of running a Markov model (a way to model discrete states) until there is convergence. He just used a Markov model the way that it is supposed to be used...
I dont get it... what's notable here?
What factorial does it take to equal that number? I know that its very easy in math to get numbers that large, but this wasn't a place I expected to find it.
FanFictionRecs.net
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.'"
The difference is, its pretty obvious to a human if a page is important. On the other hand there are a lot of species that we don't know if they are important or not. So how do we know what the "important" species are? Other than humans, we don't know of any real "important" species. Could the ecosystem survive without X? Theres no way we can really know that.
Taxation is legalized theft, no more, no less.
I've often been annoyed by the excessive focus on the iconic and popular species in many endangered species awareness campaigns. It is easy to say "we are spending a million dollars on protecting a worm?" in Congress, but when more renowned species like a hammerhead shark variety are endangered, they will naturally get more attention. Now scientists can defend their case for funding by pointing to this algorithm.
Have you learned nothing from history? We can know if an ecosystem survives without certain members.
It just isn't a good idea to experiment.
I would have thought that an animal-based algorithm such as PigeonRank would be more applicable to this problem.
The World Wide Web is dying. Soon, we shall have only the Internet.
If you're under 40 and in good health you're in for a rather rude awakening, with those beliefs. You'll likely live to see the shit begin to hit the fan in a serious way. Google and other online sources should be education enough for you. I'm too disorganized to do anything more than plant the seed; you'll have to water and feed it.
So lets see here, I'm supposed to believe some random person on the internet because of A) Sci-Fi films, B) "facts" that contradict reputable sources such as the United Nations and C) ideas that don't make much sense. Lets see here, we have technology that allows us to grow more crops in a single area than ever before, technology that lets us grow more crops with less effort (we have less humans employed as farmers than before yet have more crops than before) and technology that will let us grow crops in places that could never have had crops planted before. We similarly have lots of habitable space, more than ever before. Someone could live in the middle of the desert, yet still have food, a habitable place to live and water.
So in the end, we have more food than we know what to do with, technology enabling us if there was some kind of food shortage to grow our own food in our basements if need be, no shortage of space, etc. Seriously, part of science fiction is... fiction. If it was true, well perhaps I should start carving Ego in big letters in rocks in case humanity forgets about individuality and the word I (for those not in the know this is a reference to Ayn Rand's book Anthem). But really take a look at http://en.wikipedia.org/wiki/File:Population_growth_rate_world.PNG -large- portions of the world have a negative birth rate. So with no science to back up your claims, other than a few science fiction movies, why should I believe you?
Taxation is legalized theft, no more, no less.
The pagerank algorithm is better understood as a kind of Eigenvector Centrality Measure.
See http://en.wikipedia.org/wiki/Eigenvector_centrality#Eigenvector_centrality
Meaning it is not new as a method by itself, but applying it to the linking-structure of the WWW in order to produce
relevant documents for a query, was new. I think it is fair to say that the Google Pagerank matters very little, outside of being able to rank otherwise
not-comparable search results.
And so it is better to state that "a specialized Eigenvector Centrality Measure can predict with great accuracy which species are vital to the existence of others" instead of "a modified version of PageRank can predict with great accuracy which species are vital to the existence of others". One can see that also when one realizes that these biologists have no query, no search, no equivalent of search keywords.
On the other hand, when the post says "Co-author Dr. Stefano Allesina realized he could apply PageRank to the problem when he stumbled across an article in a journal of applied mathematics describing the Google algorithm." -- I guess he might have found the method through the Google name.
Stephan
http://stephan.sugarmotor.org