Species associations and trait dissimilarity in communities of ectoparasitic arthropods harboured by small mammals at three hierarchical scales

1. This study tested the relationships between the probability of pairwise species co-occurrence and pairwise dissimilarity in their traits in infracommunities (across assemblages harboured by conspecific individual hosts within a locality), component communities (across assemblages harboured by host species within a locality), and compound communities (across assemblages in different localities) of fleas and gamasid mites parasitic on small mammals in Western Siberia. 2. A significant, albeit weak, tendency was found for flea communities harboured by conspecific host individuals, host species, and host communities to be composed of similar species. No relationship between the probability of co-occurrence and trait dissimilarity was detected for mite communities at any hierarchical scale. 3. For fleas, this study explained the link between positive co-occurrence and trait dissimilarity by a process resembling environmental filtering realised mainly via host traits for infracommunities and component communities and via off-host environment for compound communities, thus suggesting that the identical shape of the relationships between co-occurrence and trait dissimilarity at different scales was driven by different mechanisms. 4. The explanation of the lack of this relationship in mites included: (i) the paucity of the subset of mite traits used in this study and its potential inadequacy for the question at hand; and (ii) possible masking of the effect induced by one trait on co-occurrence owing to the lack of this effect induced by another trait(s). 5. Caution is recommended regarding the compilation of a dataset involving multiple traits, its analysis, and the interpretation of the results.