Environmental disturbances of trophic interactions and their impacts on a multihost sapronotic pathogen.

Sapronotic pathogens are constituents of complex trophic networks, such as those that structure aquatic and soil ecosystems. In such habitats, sapronotic pathogens live and reproduce among microbial consortia; they also may occasionally infect hosts and cause sapronotic disease (sapronosis). Sapronotic pathogens regroup almost all fungal microparasites and about a third of the bacterial pathogens infecting humans, including for instance nontuberculous mycobacteria. Even though sapronotic agents are naturally present in the environment, their population dynamics are unknown. Despite growing rates of sapronotic disease incidence among humans, wild, and domestic animals, very few studies have examined sapronotic transmission and dynamics in the context of spatially implicit trophic networks. Patterns of sapronotic pathogen transmission arise from complex interactions, including pathogen natural history, nonhost and host environments, and spatial and temporal scales of the system. In order to infer and ultimately predict how environmental disturbances affect trophic interactions and influence sapronotic ecology, we analysed host and nonhost species interacting as prey and as micro- and macropredators within a metacommunity context. Using a set of differential equation models, we assessed responses of environmental load dynamics of a sapronotic disease agent, i.e. a mycobacterial pathogen, within a general framework of environmental disturbance. We show that variation in top-down and horizontal interactions mediated sapronotic pathogen abundance and dynamics in the environment. Our findings indicate that habitat change and trophic interactions within these host-pathogen relationships may strongly affect sapronotic pathogen ecology through both synergistic and opposing mechanisms. This work provides for the first time an understanding of environmental disturbance consequences on trophic webs that include major sapronotic pathogens. In addition, the results provide a basis for interpreting the development of sapronotic epidemics and epizootics in the context of ecosystem modifications, particularly that of agriculture and land-use transformation. Further research of this type will provide a better understanding of the complex dynamics of sapronotic pathogens in animals and humans responding to global change.