Phylogenetic and functional niche breadth in two taxa of arthropod ectoparasites: correlations with ecomorphological traits are scale-dependent

We studied the relationships between phylogenetic (PNB) and functional (FNB) niche breadth and abundance and body size in fleas and gamasid mites in multiple regions across the Palearctic. We asked whether (a) PNB or FNB correlated with abundance or body size; (b) the pattern of this correlation differed between the regional (within a region) and the continental (across regions) scales; and (c) the regional PNB and FNB of a parasite was affected by the phylogenetic and functional, respectively, diversity of all hosts in that region. The relationships between abundance and PNB or FNB were mainly manifested on the continental scale, but mostly not on the regional scale, being positive in both taxa. The effect of body size on PNB and FNB was found in only a few regions for fleas and in no regions for mites. On the contrary, continental PNB and FNB did not correlate with flea body size but decreased with an increase in mite body size. Regional PNB and FNB values of some, but not all, flea and mite species were positively associated with the phylogenetic and functional, respectively, diversity of hosts available in a region. We conclude that the relationships between the abundance and body size of an ectoparasite and its PNB or FNB are scale dependent. These relationships may differ from or be similar to the relationships between abundance or body size and niche breadth measured as the size of a host spectrum, depending on spatial scale and ectoparasite taxon.