It's all about scale: The landscape effect on avian haemosporidians.

Environmental characteristics drastically shape the host-parasite associations under natural conditions. This is the case of parasites such as avian haemosporidians which naturally infect birds and are transmitted by insect vectors. Landscape characteristics are known to determine the epidemiology of transmission of these parasites in the wild, but the strength of these factors may differ at different spatial scales. We studied the effects of the landscape structure and environmental variables on the prevalence and richness of lineages of avian haemosporidian parasites (genera Plasmodium, Haemoproteus and Leucocytozoon) infecting birds in a highly diverse area of Antioquia, Colombia. We screened blood samples from 678 individuals across 90 bird species for number of infections, prevalence and richness of haemosporidian lineages in sites surrounding three hydroelectric dams. We obtained environmental and landscape structure variables around the bird sampling points at different spatial scales (from 50 to 500 m radii, every 50 m) and selected the most important ones. We modelled the relationships between parasite infection variables and landscape structural and environmental characteristics. Effects of landscape structure on variables reflecting haemosporidian infections varied according to the selected scale of analyses. The scale of the effect of landscape structure was larger for the number of infections and prevalence (Average = 350 and 425 m radius) than for lineage richness (Average = Plasmodium 219 m, Haemoproteus 244 m). Agricultural patch density notably increased number of infection rates (pseudo-R = 0.68). The number of infections and the richness of Haemoproteus lineages correlated with agricultural connectivity at larger scales (500 m). Haemosporidian prevalence was primarily linked with proportion forest and agricultural covers. Haemoproteus richness was influenced by connectivity and NDVI - Normalized Difference Vegetation Index (pseudo-R = 0.83), while Plasmodium richness was affected by anthropogenic density, edge density, forest proportion, and temperature (pseudo-R = 0.79). Changes in parasite infection and prevalence remain difficult to predict, as each parasite-host system is susceptible to many unaccounted variables. This study found that transformed landscapes, particularly density of anthropogenic and agricultural patches nearby increases haemosporidian parasites at different scales. These findings underscore the complex interplay between landscape structure and haemosporidian infections in avian hosts in tropical ecosystems.