Phylogenetic and Functional Originality Shape Species Positions in Flea–Mammal Networks Across Biogeographic Realms

We investigated the relationships between a species' network position (measured as the combined normalized degree, species strength, and betweenness centrality) and its phylogenetic or functional originality, using 91 flea-host interaction networks from four biogeographic realms (the Afrotropics, the Nearctic, the Neotropics, and the Palearctic). The originality of a species was measured either via the topology of a phylogenetic tree/functional dendrogram (tree-based index) or as the minimal phylogenetic/functional distance from another species in the same assemblage (distance-based index). Significant relationships between a flea species' position and functional originality were positive in all realms independently of the index used, suggesting that functionally original species were characterized by higher combined species degree, strength, and betweenness centrality. Higher values of these components of the network position were detected in the most phylogenetically original Neotropical fleas using the tree-based index and the least phylogenetically original Afrotropical and Palearctic fleas using the distance-based index. A host species' network position was associated with its phylogenetic originality in the Nearctic (positive) and the Neotropics (negative) but only when the distance-based but not the tree-based index was used. No effect of a host's functional originality on its network position was found in any realms independently of the index used. We conclude that the pattern of the relationship between phylogenetic and functional originality and species position in a flea-host network differed substantially between (a) fleas and hosts and (b) biogeographic realms.