(color online) An optimal node hierarchy for the Florida food web^[19] and the corresponding feedback arcs. The whole network has 128 nodes and 2106 arcs, and its largest strongly connected component contains 103 nodes and 1579 arcs (for clarity only this component is shown). The nodes (black dots) are arranged to 22 hierarchical levels starting from level 0 at the bottom. Gray solid lines are feedforward arcs (pointing from higher-level nodes to lower-level nodes), and red dashed lines are feedback arcs (pointing from lower-level nodes to higher-level nodes). Each blue dotted line represents a pair of opposite arcs between two nodes.