Avian haemosporidian distributions in South America shaped by host distributions but not by climate or distance

Understanding the forces that shape species distributions remains a central goal in ecology. These forces include colonization ability, environmental filters such as climate, and biotic interactions. Additionally, the distributions of vector-transmitted parasites can be influenced by host- and vector-switching and by host and vector dispersal. We sampled birds and their haemosporidian blood parasites (Plasmodium and Haemoproteus) at sites across South America and used Mantel tests to examine how host communities and parasite assemblages vary with each other, with climatic variation, and with distance. Across sites, we sampled 6,836 birds and identified 1,091 infections in 481 lineages (336 Plasmodium, 145 Haemoproteus). Parasite assemblages reflected the distributions of their avian hosts, but the amount of variation explained was low (19.2%). When controlling statistically for host community, parasite assemblage similarity was not related to climatic variation or to distance between sites. Furthermore, similarity of parasite assemblages did not decrease with distance when controlling for host community or climate, suggesting that parasite lineages are well dispersed within the ranges of their host species. When examined separately, Plasmodium and for Haemoproteus assemblages showed similar results. In contrast, bird community similarity decreased with differences in climate and with distance, even when controlling for parasites. Bird community similarity decreased with distance even when controlling for climate, suggesting that bird species are dispersal-limited. Together, our findings suggest that distance and climate influence bird distributions and the distributions of avian hosts influence the distributions of their haemosporidian parasites, but climate and distance do not influence parasite distributions directly.