Species associations in arthropod ectoparasite infracommunities are spatially and temporally variable and affected by environmental factors

1. We applied a Markov random fields/conditional random fields (MRF/CRF) modelling to understand whether and how species associations in ectoparasite infracommunities of small mammals vary along environmental gradients across space and time. 2. We analysed the variation in species associations in flea and mite infracommunities of seven host species across localities (spatial scale) and time periods (in the same locality; temporal scale). 3. The performance of the CRF models differed between ectoparasite taxa, scales, and host species. The model performance for flea and mite infracommunities in the majority of host species was satisfying although the proportions of correctly predicted positive occurrences and model sensitivity were moderate. 4. The probability of occurrence of many flea and mite species depended mostly on the occurrence of another flea and mite species (respectively), with many negative interspecific interactions, although occurrences of some species were mainly affected by environmental factors. The patterns of pairwise associations between some ectoparasite species were affected by environmental factors. 5. Although many ectoparasite pairs demonstrated stability in the strength or sign of association across space or time, interactions between other species pairs were spatially or temporally variable, with the association between the same pair of species being stable in one host species and variable in another host species. 6. We conclude that ectoparasite associations are mediated by the off-host environment and may depend on the life histories of both host and ectoparasite species.