Revisiting a trophic overlap-based measure for species uniqueness in ecological networks

Species uniqueness can be measured from the network perspective offering an alternative view to species importance. Direct and indirect effects between species can be quantified to construct a matrix that represents the interaction structure of the food web. Such a matrix is then used to determine the trophic fields of individual species; and the uniqueness of a species is defined based on the extent of overlap between its trophic field and those of other species (TFO-based index). In this paper, we revisit this former idea of species uniqueness and demonstrate how its computation can be simplified. Here, from the interaction matrix we construct a distance matrix where an element of this matrix is the distance between the interaction profiles of a particular species pair; and the row sums of this distance matrix are the uniqueness values of species in the food web. We offer two approaches depending on the type of distance calculated. The Manhattan distance-based index produces identical ranking of species uniqueness as the TFO-based index, while the Euclidean distance-based index shows strong correlation with the TFO-based index. Lastly, we describe a basic framework for quantifying species uniqueness from the network perspective as a potential direction for future research.