 So, I don't know how many of you are aware, but we are in the middle of mass extinction of species right now, but we still don't understand the consequences of this widespread loss of species. We can describe and depict ecological ecosystems like network of species interacting each other via predatory links and the study of food web which is this network of species is based on these matrix, but the problem with these matrix is that they don't give us a lot of information about a single node by just the general structure of the network. So, this is my wall and my suggestion to break it is to use what is called network theory which developed is on its own matrix like this one that can give us information about a specific node in the network. I will show you an example. This is the cat's centrality which give us an information about with how many species a particular node will interact. I scaled the Serengeti ecosystem food web which is this one for every species for its particular cat's centrality. So, the size of a node is directly proportional to its centrality. At this point I can ask where is a particular species for example the elephant. It's here which relatively high centrality and a lot of neighbors and I may ask also where is the lion for example. The lion is here. The important is not the position of the species in this case but the size of the node. And we can see that the lion has a relatively low cat's centrality. But what's the most central species in the network? It's just a small hyrax. This is quite unexpected from a pure ecological point of view especially for the lion which is a top predator. This is just an example of the new kind of information that we can access through network theory. And finally I will finish my time with a consideration which is that food webs are complex systems and to study complex systems we need an holistic approach and network theory is conveniently an holistic approach that can help us in slowing down the current extinction rate and preserve the decline in biodiversity. This is just an example. It was a giant sloth, ground sloth three meters high that went extinct some thousand years ago due to spread of Homo sapiens in South America. Question?