Guilhaumon F, Krasnov BR, Poulin R, Shenbrot GI and Mouillot D.

Aim  The large-scale description of ecosystem complexity, including the structure of interaction networks, has been largely overlooked although it is known to underpin species co-occurrences and their robustness to climatic or anthropogenic disturbances. Here, we investigated whether the various components of mammal–flea interaction networks (richness of fleas, richness of mammals and the richness of mammal–flea associations) are spatially congruent and follow the latitudinal diversity gradient (LDG).

Location  Sixteen regions, world-wide.

Methods  We first took into account the effect of area on diversity by determining the position of regions with respect to species–area relationships. We then investigated the spatial congruence between the regional richness of each component of mammal–flea interaction networks as well as their latitudinal gradients. We further investigated patterns for flea–host associations by testing for relationships between mammal–flea interaction richness and (1) flea niche breadth and (2) host carrying capacity.

Results  We report divergent LDGs for the different components of mammal–flea interaction networks: our data agree with a canonical LDG for mammals, but reveal that the diversity of fleas and mammal–flea associations do not follow such a classical gradient. Our results suggest that host carrying capacity is more likely than flea niche breadth to modulate the number of links in host–parasite interaction networks.

Main conclusions  The complex interplay between geographic variation in host diversity and both host and parasite traits can lead to unexpected spatial patterns such as the invalidation of expected parasites and links in host–parasite web LDGs. Beyond our focus on host–parasite interactions, our study is among the first in the emerging field of interaction network macroecology and paves the way for other components of ecological networks to be investigated across space and time.