Our understanding of the drivers of parasite community structure is compromised by poor sampling and historical focus on one host-one parasite systems. Yet parasites are ubiquitous and co-infections are common. This study aimed to identify how a range of drivers (connectivity, region, host-parasite interactions, parasite-parasite interactions) contribute to structuring endoparasite metacommunities. Within-host to landscape level patterns of malacosporean myxozoans infecting dormant propagules (statoblasts) of the freshwater bryozoan, Cristatella mucedo, were characterised. Large-scale databases were used to develop a metric for waterbird connectivity based on species turnover. Overall infection prevalence, assessed by PCR, was associated with high waterbird turnover at the site level, providing evidence that waterbirds act as parasite dispersal vectors. RFLP analysis revealed eight malacosporean infection profiles. Traits of both hosts (e.g. habitat preferences) and parasites (e.g. transmission success) were linked with impacts of hydrological connectivity. Flooding regimes, nutrient enrichment from agriculture landscapes, and waterbird abundance were linked with regional impacts. Co-infections within tiny statoblasts (up to four) were common. Uninfected statoblasts were larger and there was no detectable difference in sizes of statoblasts with single vs. multiple infections. Co-occurrence analysis identified positive associations between four malacosporean taxa. The lack of negative associations suggests no competition amongst malacosporeans infecting statoblasts. There was no evidence that host-parasite interactions result in local adaptation of parasites to host clones. Hydrologically isolated sites had greater malacosporean diversity and enhanced levels of overall infection prevalence and co-infection, suggesting that such sites are malacosporean hotspots. Our study provides novel insights on the complex factors that can structure parasite communities in freshwater invertebrate hosts across the UK.

Ireland and Britain are two islands located at Europe’s westernmost edge, both of which act as the final breeding outposts for many bird species within their European ranges. Despite their similar geographic locations and geological histories, Ireland and Britain host different breeding avifauna assemblages. Diversity profiles, which can serve as more robust alternatives to classic diversity indices, were employed in this study to explore disparities in the two islands’ breeding avifauna assemblages. Variations in assemblages were explored, along with their potential drivers, through analyses at three levels: island-scale breeding bird assemblage compositions, island-scale diversity profiles considering 49 common breeding species, and habitat-specific diversity profiles considering assemblages in east/central Irish farmland and East Anglian farmland. Analysis of the two islands’ breeding avifauna assemblages revealed that the Irish assemblage is a complete subset of the British assemblage. Analyses of Irish and British assemblages at both an island scale and a habitat scale revealed patterns linking land use to trends within the two islands’ avifauna assemblages. Irish assemblages contained greater proportions of insectivorous farmland species by abundance, while British assemblages contained greater proportions of seed-eating farmland species; both trends appeared to be related to structural differences in agricultural land use on the two islands. The British and East Anglian assemblages exhibited higher diversity across all analyses, which appeared to be driven by the assemblages’ higher relative abundances of species that were most genetically distinct. This study highlights the ability of diversity profiles to impart more information than classic diversity indices by incorporating species similarity data.