Figure 4. Null distribution of the ß-diversity of interactions (ßTL) at fixed trophic group diversity. The values of the histogram show the ßTL between the average food webs of forest and grassland computed using 3000 permutations of trophic group abundances at fixed network structure, leading to various ßTL values while keeping trophic group ß-diversity constant. The vertical line shows the observed ßTL across habitats. The value of ßTL varies from one when the average food web of forest and grassland have identical interaction abundances distribution, to two, when the food webs do not share any common group or interaction.