In theory, animal diets may act as important filters for different parasite species. However, there is currently a lack of empirical research looking at host diet as a potential predictor of parasite diversity among different host species. The aim of this study was to assess the influence of several host diet features (including diet breadth, diet composition, and trophic level) on tapeworm diversity in sharks, relative to other key factors, including host size, habitat, phylogeny, latitude, and depth. Data on these host features were compiled from a comprehensive analysis of literature records including 91 different shark species, and 3 measures of tapeworm diversity were examined: tapeworm species richness, tapeworm taxonomic distinctness (TD), and variance in tapeworm TD. The diet breadth of a shark species was revealed to be a better predictor of tapeworm species richness than other host features examined to date. Host size, trophic level, diet TD, latitudinal range, and the mid-point of a shark's depth range also significantly influenced tapeworm richness when analyses were ad justed to prevent confounding by phylogenetic re lation ships between hosts. The TD of tapeworm assemblages was influenced by diet breadth, diet TD, host size, and depth range when analysed independently of host phylogeny. Overall, our findings demonstrate that aspects of host diet have important consequences for parasite diversity in sharks. We em phasise that studies of parasite diversity in other systems should more seriously consider including aspects of host diet (particularly diet breadth) as potential key predictors of parasite diversity.

The impact of parasites on host population dynamics depends on local abundance of the parasites, which may vary considerably across spatial scales. In sand hopper populations, mermithid parasites have major impacts on host dynamics, which may vary among spatially separated populations due to the sand hopper's wide, patchy distribution. The present study compared the abundance and biomass of a mermithid parasite (Thaumamermis zealandica Poinar et al., 2002) in sand hoppers (Bellorchestia quoyana (Milne-Edwards)) both within and among disconnected beaches. In addition, several variables were measured and tested as potentially important predictors of the parasite abundance and biomass. It was found that geographic isolation may only be responsible for minor differences in parasite populations compared with other factors. Host size was identified as the most important predictor of mermithid parasite abundance, but epibiont abundance, kelp patch mass and host density were poor predictors of abundance. These factors were also poor predictors of parasite biomass in hosts. This study further supports the notion that studies aiming to elucidate population dynamics or patterns should sample thoroughly across both spatial and temporal scales.