Geographic patterns of functional and phylogenetic niche breadth in Holarctic fleas (Siphonaptera)

We studied geographic patterns of functional and phylogenetic niche breadth of 194 flea species. Niche breadth was measured as the functional and phylogenetic diversity and uniqueness of the assemblages of small mammal hosts exploited by these fleas.We asked (a) whether the relationships between niche breadth and geographic range size conform to the ‘niche breadth hypothesis’, predicting positive correlations, and (b) whether variation of niche breadth along the latitudinal position of geographic range conforms to the ‘niche breadth-latitude hypothesis’, predicting narrower niche breadth at lower latitudes. We found that the functional and phylogenetic diversity, but not the functional and phylogenetic uniqueness, of the host assemblages demonstrated patterns conforming to the prediction of the ‘niche breadth hypothesis’. Host assemblages exploited by broadly distributed fleas tended to be functionally and phylogenetically more diverse than those of fleas with a restricted geographic distribution, but the functional and phylogenetic uniqueness of hosts decreased in more broadly distributed fleas. The phylogenetic diversity of hosts exploited by a flea did not vary with the latitudinal position of the flea's geographic range. In contrast, the functional diversity and both the functional and phylogenetic uniqueness of hosts decreased from south to north, thus contradicting the predictions of ‘the niche breadth-latitude hypothesis’. Comparing these and earlier results on the geographic patterns of flea niche breadth, we conclude (a) that compositional, functional and phylogenetic diversity could be similarly driven by some factors and differently by other factors and (b) that these diversity facets are not always good surrogates for each other.