Geographical range size and host specificity in ectoparasites: A case study with Amphipsylla fleas and rodent hosts

Aim: To identify the factors that determine the geographical range sizes of ectoparasites with different degrees of host specificity. Location: The study used data on the distributions of fleas of the genus Amphipsylla and their rodent hosts across the Holarctic. Methods: All known points of occurrence of 32 flea species and 51 species of their rodent hosts were mapped. The shape and size of the geographical range of each species were estimated using a combination of the minimal convex polygon technique and modelling with the garp algorithm. Factors determining the geographical range sizes of the fleas were identified using stepwise multiple regression analysis. Results: The geographical range size of fleas that are strongly host-specific across their entire ranges correlated positively with the geographical range size of the fleas' principal hosts, and negatively with the geographical range size of the fleas' potential competitors. The geographical range sizes of both (1) fleas that are locally host-specific but that shift their host preferences geographically, and (2) host-opportunistic fleas were positively correlated only with the area of the geographical ranges of their principal hosts. Strongly host-specific fleas occupied 0.2-80.0% of the geographical range of their principal hosts, whereas this figure was 0.9-83.7% in locally host-specific fleas and 16.6-63.7% in host-opportunistic fleas. Main conclusions: The main determinant of the geographical range size of a flea species is the size of the geographical range of its hosts. The role of potential competitors in determining the geographical range size is stronger in host-specific than in host-opportunistic fleas. Cases in which the geographical range of a parasite is smaller than the geographical range(s) of its host(s) owing to narrower parasite environmental tolerances are much more frequent in host-opportunistic than in host-specific fleas.