The latitudinal patterns of phylogenetic, functional, and numerical interaction specificity in flea-mammal networks vary between biogeographic realms

The latitudinal patterns of the phylogenetic, functional,and numerical interaction specificity (PIS, FIS, and NIS, respectively) of fleasand mammals in their interactionnetworks,from four biogeographic realms,were investigated at the intraspecific, interspecific,and community levelsto understandwhether the spatial variation of interaction specificity followed the predictions of a latitudinal specialization gradient. In fleas, no latitudinal pattern of PIS was detected. FleaFIS varied with latitude in all realms at the intraspecific level and in two realms at the interspecific and community levels. Latitudinal trends in NIS were detected in all realms (except Neotropics)at the intraspecific level and in the Old World realmsat both higher levels. In hosts, PIS varied with latitude in the Afrotropics and the Nearctic at the intraspecific level and in the Afrotropics at theinterspecific and the community levels. FIS demonstrated a latitudinal trend in the Nearctic at the intraspecific level and in the Palearctic at the community level. Relationships between latitude and NIS were found in all realms (except Neotropics)at the intraspecific level and in the Old World realmsinterspecific and communitylevels. The directions of the latitudinal pattern of the same specificity facet could be positive or negative. Theydiffered between fleas and hosts, realms, and organizational levels.The occurrence and direction of the latitudinal specialization gradient areexplained by the combined actions ofevolutionary, historical,and ecological factors. Pooling data from regions with different biogeographical histories and landscape structures,for a macroecological analysis,may produce spurious results.