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.'"

Why is this surprising?

[Anonymous Coward]

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?

More than atoms in the universe?

[JordanL]

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.

Importance

[Darkness404]

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.

Very helpful for Endangered Species Act

[Kligat]

I've often been annoyed by the excessive focus on the iconic [washingtonpost.com] 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.

Re:But solve the real problem?

[Darkness404]

Please tell how you think we are currently becoming overpopulated? For one we have enough food to feed -everyone- the problem is corrupt government and lack of education that causes hunger in third-world countries. In first world countries its quite easy to get food and shelter so no one should ever die of hunger. Yeah, you won't be eating steak and shrimp every night, but you aren't going to starve to death. Take a drive to North Dakota sometime if you don't think we have enough space. If you read the UN's projections for birth rates (http://www.un.org/esa/population/publications/wpp2006/WPP2006_Highlights_rev.pdf) it shows a -sharp- decline in birth rates for most of the developed world. And in general a "bubble" of population increase then a decrease (because there is a large amount of old people who are going to die). Even a doubling in human population isn't really a huge deal with increasing technology leading to increased crop yields and the ability to farm previously unfarmable areas. And we have way more than enough space.

Re:More than atoms in the universe?

[cmseagle]

Yeah, I would tend to call BS on that particular statistic. Let's say the average water bottle is .5L. In that one, single water bottle that is sitting on my desk, there are 5.01*10^25 atoms. That's one hell of a number.

Now, let's pretend God has a really good magnifying glass and a really small set of tweezers, and he's removing atoms from this water bottle at a rate of 1 per second. Conservative estimates put the universe at 13.5 billion years old, which converts to 4.25*10^17 seconds.

So, since the beginning of time, God has removed 4.25*10^17 atoms from my water bottle. A lot, right? Not quit. (4.25*10^17)/(5.01*10^25)=8.00*10^-9.

Even removing an atom every second since the beginning of time, only a few trillionths are missing from my bottle of water. That's just a bottle of water, now imagine the number of atoms in the ocean, or in the sun. Something does not seem right with the "More than number of atoms in the universe" claim.

Re:But solve the real problem?

[Darkness404]

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 [wikipedia.org] -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?