Name:	Food Webs
Description:	Food Webs are graph representations of the predatory interactions among species in a given environment. Each vertex in the graph represents a species and is labelled by an integer number i=1,...,N. If species i preys on species j, then a directed link is drawn from j (the prey) to i (the predator). TOP species are those with no predator, BASAL species are those with no prey and INTERMEDIATE species have both predators and prey. Species with no prey must necessarily feed on a set of abiotic resources (water, light, chemicals) which is commonly referred to as the "environment vertex" and labelled by 0 (also non-basal species can feed on the environment vertex). The total number of vertices in a food web is therefore N+1 (in the data table below, the number N+1 is reported for each food web). Actually, in the Silwood Park food web, the "environment vertex" is a biological species (Scotch Broom) itself, and all other species in the web prey directly or indirectly on it. Since every species must feed on at least one species, which in turn must do the same (and so on until one reaches the environment), the environment vertex can be reached from every species following a suitable set of links. In this sense, food webs are connected directed graphs. The present database contains a set of 6 food webs from different environments and of different composition. Due to the difficulty in recording every species in the environment and every interaction among them, generally food webs are very small graphs (less than 200 vertices). Their topological complexity is however fundamental and deeply related to their stability and functional optimization.
About this Data:	Data are converted in the standard format of this website (SOURCE VERTEX -> TARGET VERTEX) from a series of ecological papers (see reference for each data set). Within the context of food webs, this means that the format is (PREY -> PREDATOR).
Properties:	directed, connected
Data:	File Nodes Edges Comment Little Rock Lake 182+1 2494 (none) Grassland 87+1 137 (none) Silwood Park 153+1 370 See Description St. Marks Seagrass 48+1 226 (none) St. Martin Island 44+1 224 (none) Ythan Estuary 134+1 601 (none) The files are in format (x y) where x is the prey and y is the predator, which are connected by a directed edge.
Used in:	Many papers!
Comments:	(none)

Further Information on Little Rock Lake at Neo Martinez page
Further Information on St. Marks at Joseph J. Luczkovich page