Abstract
A parasite's ability to be a specialist vs. a generalist may have consequences for its prevalence within one or more if its host species. In this study we investigated the relationship between host specialization and prevalence in the highly species diverse avian blood parasites of the genera Plasmodium and Haemoproteus . Contrary to trade‐off hypotheses that may explain host specialization, within both genera the parasites with the ability to complete their life cycles and be transmitted across a wide host range (broad compatibility) were also the most common parasites within their compatible host species. These patterns remained unchanged when the host species with the highest prevalence were excluded, which reduces the possibility that the observed pattern was caused by parasites reaching high prevalence in a single main host, and being “spilled over” to other host species. We hypothesize that a positive relationship between parasite host range and prevalence might be explained by an overall higher encounter rate for the parasites with broad host range, which compensates for possibly reduced performance of parasites in each host species. Overall, these results show that parasites with the ability to successfully infect a wide variety of host species of broad ancestry also can have the ability to be the most prevalent in single host species.