Compositional turnover in host and parasite communities does not change network structure

16 November 2017

Dallas, Tad ; Poisot, Timothée

Decreasing similarity between ecological communities with increasing geographic distance (i.e., \textit{distance-decay}) is a common biogeographical observation in free-living communities, and a slightly less common observation for parasite communities. Ecological networks of interacting species may adhere to a similar pattern of decreasing interaction similarity with increasing geographic distance, especially if species interactions are maintained across space. We extend this further, examining if host-parasite networks -- independent of host and parasite species identities -- become more structurally dissimilar with increasing geographic distance. Utilizing a global database of helminth parasite occurrence records, we find evidence for \textit{distance-decay} relationships in host and parasite communities at both regional and global scales, but fail to detect similar relationships in network structural similarity. Host and parasite community similarity were strongly related, and both decayed rapidly with increasing geographic distance, typically resulting in complete dissimilarity after approximately 2500 km. Our failure to detect a decay in network structural similarity suggests the possibility that different host and parasite species are filling the same functional roles in interaction networks, or that variation in network similarity may be better explained by other geographic variables or aspects of host and parasite ecology.