From Graphs to Spatial Graphs

Graph theory is a powerful body of mathematical knowledge, based on simple concepts, in which structural units are depicted as nodes with relationships between them depicted as lines. The nodes may have qualitative and quantitative characteristics, and the edges may have properties such as weights and directions. Graph theory provides a flexible conceptual model that can clarify the relationship between structures and processes, including the mechanisms of configuration effects and compositional differences. Graph concepts apply to many ecological and evolutionary phenomena, including interspecific associations, spatial structure, dispersal in landscapes, and relationships within metapopulations and metacommunities. We review applications of graph theory in biology, emphasizing graphs with spatial contexts. We show how spatial graph properties can be used for description and comparison as well as to test specific hypotheses. We suggest that future applications should include explicit spatial elements for landscape studies of ecological, genetic and epidemiological phenomena.