# Environmental and host- and parasite-associated drivers of the flea-mammal interaction network structure differ between biogeographic realms

## TL;DR

The study shows how climate, host, and parasite factors differently shape mammal-flea interaction networks across different regions of the world.

## Contribution

The study reveals that drivers of network structure vary between biogeographic realms due to ecological and historical factors.

## Key findings

- Climatic drivers of nestedness and modularity differ between biogeographic realms.
- Host species richness mainly affects nestedness, while flea species richness affects modularity.
- Dissimilarity in host-sharing-by-fleas networks is linked to host and flea dissimilarities, but not for flea-sharing-by-hosts networks.

## Abstract

We evaluated the effects of climatic factors, host and parasite species richness, and their phylogenetic and functional diversity on the nestedness and modularity of mammal-flea interaction networks from four biogeographic realms. We also tested for the associations between pure structural network dissimilarity (i.e., dissimilarity between host-sharing-by-fleas networks, Dh, or dissimilarity between flea-sharing-by-hosts networks, Df) and environmental dissimilarity, and host and flea compositional, phylogenetic, and functional dissimilarities. We asked whether (a) the relative effects of these factors differ between biogeographic realms and (b) the network structure is more strongly driven by environmental, geographic, host-associated, or flea-associated factors. The climatic drivers of nestedness and modularity differed between realms. The networks in different realms responded to different factors, with the directions of some of these effects being opposite. Among interactor-associated factors, host species richness was most often detected as an important driver of nestedness, whereas flea species richness mainly affected modularity. Dh was mostly explained by host-associated and, to a lesser extent, flea-associated dissimilarity. No effect of host-associated dissimilarity on Df was detected, but it was linked with flea-associated dissimilarity in two of the four realms. Environmental dissimilarity weakly affected Dh and did not affect Df. We conclude that between-realm differences in the drivers of network structure resulted from an interplay of ecological and historical factors, whereas between-interactor differences in their effects on the network structure arose due to the asymmetry in host-flea relationships.