Macroecologia de parasitos: como espaço, clima e hospedeiros determinam a diversidade de helmintos em amplas escalas espaciais

Abstract

One of the goals of macroecology and biogeography as scientific endeavours is to discover general principles that govern biological diversity regardless of biological group or the studied system. In particular, studying parasite alpha and beta diversity at broad spatial scales presents some significant challenges. These organisms live in close association with their hosts, which adds a level of complexity that if ignored can result in wrong conclusions. For instance, climate and host richness are important drivers of parasite alpha diversity at the macroecological scale, but their effects are typically treated separately, despite the possibility of interactions. In relation to beta diversity, most large-scale studies have either focused on mammalian ectoparasites or on the Palearctic realm, which presents opportunities to investigate novel realms and host groups in order to advance the generality of parasite macroecological theory. Furthermore, to the best of our knowledge, no large-scale study has been conducted to investigate how the drivers of parasite beta diversity vary with scale. Based on a novel dataset of helminth parasites of amphibians, we used structural equation modelling to investigate the direct and indirect effects of climate and host richness as drivers of parasite alpha diversity at the global scale. Furthermore, we used generalized dissimilarity modelling to investigate how the relative roles of climate, host diversity, and spatial distance as drivers of parasite beta diversity vary with spatial scale (global vs regional) and zoogeographical realm (Nearctic vs Neotropical). Additionally, we investigated whether selecting distinct host taxonomic subsets (families) influences general trends in parasite beta diversity. First, we found that climate affects global parasite richness both directly and indirectly via host richness. These findings are important in the context of cascade co-extinctions caused by climate change, and they emphasize the importance of using analytical approaches that allow for the evaluation of indirect relationships among predictors. In relation to parasite beta diversity, we found that spatial distance is the strongest predictor of parasite turnover at the global scale and that its relative importance in relation to climate decreases at the regional scale. In addition, we demonstrated that the relative importance of our predictors varies with the zoogeographical realm. Interestingly, we found contrasting results when comparing different host families collected in the same realm. Given that biological differences between hosts can result in diverging pressures for parasite colonization and persistence, this may warrant further investigation. The take-home message from this discovery could be the importance of including host life-history specifically in parasite beta diversity studies at the macroecological level. Such contingencies are an opportunity for further exploration, as they have important implications for the search for universal drivers of parasite diversity at large scales. Our study is an important new contribution to parasite macroecology, integrating predictors of parasite alpha diversity and investigating the role of spatial scale, bioregion, and host taxonomic subset on parasite species turnover across geographic space. To the best of our knowledge, this is the first study on parasites to take these approaches on such a large scale.