I'm a math major with a current interest towards network theory. A network can be considered as a collection of nodes, and edges between these nodes signifying some relation between them. The most ubiquitous example would be a social network like Facebook with nodes representing people, and an edge connecting two nodes if they're friends.
A network is called directed if the edges have a direction. This means that if there's an edge directed from A to B, it's not the same as an edge from B to A. An example of this would be a food web network, where the nodes represent species and an edge from species A to B means that A eats B. Obviously, this does not necessarily mean that there's an edge from B to A (rarely does the prey eat the predator).
A network is called undirected if it is not directed, i.e. none of the edges have any direction; if there's an edge from A to B, it necessarily means that there's an edge from B to A.
Now, one can assign weights (numerical values) to the edges in a network to signify the relative importance of edges. In the Facebook example above, this can be considered akin to assigning values to edges which indicate the strength of friendship/distance between the residences of friends, etc.
I wish to study ecological networks to see if I can make interesting inferences from my study of weighted networks.
So can you give me some examples of undirected, weighted ecological networks?