Food-web-based comparison of the drivers of helminth parasite species richness in coastal fish and bird definitive hosts

Studies on the factors determining parasite richness in hosts are typically performed using data compiled for various sets of species from disparate habitats. However, parasite transmission is embedded within local trophic networks, and proper comparisons among host species of the drivers of parasite richness should ideally be conducted among hosts belonging to the same local network. Here, we used data from 6 well-resolved coastal food webs that include parasites to investigate patterns and drivers of species richness of trophically transmitted helminths in coastal fish and bird definitive hosts. We first investigated whether previous notions that birds harbour more trophically transmitted parasite species than fish hold true for food-web-based comparisons; then we investigated the roles of host prey range, trophic level and body size in driving parasite richness patterns in coastal birds and fish. Our analyses indicated that bird hosts, on average, harboured higher parasite richness than fish hosts. While there was no consistent driver of parasite richness at the level of entire food webs, host prey range and host trophic level were positively correlated with parasite richness in birds within individual food webs. For fish hosts, the effect of host prey range was less consistent and trophic level had no effect on parasite richness. Host body size did not affect parasite richness for either host type. These results suggest that host prey range and trophic level seem to be more consistent drivers of parasite richness for coastal bird than for fish hosts.