Article | Revisiting dilution and barrier to better disentangle their effects on epidemics

Rimbaud, L., Fabre, F., Roques, L., Papaïx, J., (2026) Revisiting dilution and barrier to better disentangle their effects on epidemics. In press. doi.org/10.1086/742786

Abstract: In epidemiology, the dilution effect and the barrier effect are two commonly cited processes for explaining disease limitation in biodiverse host communities. However, because these effects often operate simultaneously, clearly disentangling them is challenging. To make the underlying mechanism explicit, we therefore adopt the term “growthdilution” for the (restrictive) dilution pathway. Specifically, we define the growth-dilution effect as any process that decreases the pathogen’s local growth rate due to host individuals with lower competence to disease. In contrast, the “barrier effect” refers to processes that mitigate the pathogen’s dispersal ability, arising from physical or functional structures. Using these definitions in a spatially explicit, epidemiological model in a heterogeneous host population, we investigate the impact of these two effects, both individually and in combination, on two key metrics of disease spread: the basic reproduction number (R0, which gives insights into the probability of pathogen invasion) and the epidemic velocity. Our results show that conclusions depend on the metric considered and subtle interactions between landscape fragmentation and the spatial association (or segregation) of growth-dilution and barrier effects.