This project is intended as an example of how the structure of a network is related to its stability and at the same time as an illustration of how difficult it can be to settle the actual structure of a real network.

(a) Think of an ecological food web. Try to think about how the number of links attached to a node, i.e. a species, will influence its viability.
A keystone species is one that if removed will trigger a major upheaval in the ecosystem.
Bees are examples of keystone species.

(b) Try to consider how you will imagine the relation between stability of a species and the number of links between this species and other species in the food web.

(c) How do you expect a keystone species to be placed in terms of network structure in a food web?

Now we turn to two ecological papers [226, 416], which attempted to address the the link between structure and stability of food webs.

(d) Make a list of the most important points in [416] and summarise in particular how the authors describe the relation between the structure, or topology, of the food webs and a food web’s stability.
(e) Summarise briefly the focus of reference [226].
(f) What is the main difficulty according to [226] in identifying keystone species from food web data.
(g) Nowthink of a network describing social interactions.Consider howwe can reliably identify key persons in such a network. You can e.g. focus on decision making in a parliamentary democracy.