Ectoparasites are more vulnerable to host extinction than co-occurring endoparasites: evidence from metazoan parasites of freshwater and marine fishes

The extinction of fish species can direct and indirectly affect many groups of associated species, among which parasite communities can be the most susceptible. However, the intensity of this effect depends on the structure interaction networks. This study evaluated whether networks constituted of fish ectoparasites or endoparasites differed in their robustness to the loss of host species and to what extent these potential differences are explained by the network structures. We used path models to evaluate the direct and indirect effects of host and parasite richness, connectance, and nestedness on the robustness of ecto- and endoparasite-based networks. In most cases, nestedness was the descriptor that best explained the robustness of the fish-parasite networks, and co-extinctions are less likely when the fish species act mainly as hosts of the generalist parasites. Both the richness of the host species and connectance in the networks have an essential indirect influence on robustness. Regardless of the extinction sequence, the ectoparasite-based networks showed higher vulnerability to host species loss when compared to endoparasite-based networks. These findings highlight the importance of considering both ecto- from endoparasites to better understand the structure and vulnerability of host–parasite networks.