Community assembly processes may provide a predictive framework for understanding the mechanisms underlying disease dilution (reduced disease prevalence with increasing biodiversity). The effect of ...biodiversity on disease prevalence may depend both on a heterogeneity in host traits related to disease spread and on the order of species loss in community disassembly. If host communities decay to a predictable subset of hosts, disease prevalence may reflect the competence of the remaining hosts. To test this hypothesis, we measured local host species abundance and prevalence of four generalist aphid-vectored pathogens (barley and cereal yellow dwarf viruses, Luteoviridae) in a sentinel ubiquitous annual grass host (Bromus hordeaceus, Poaceae) at 10 sites spanning 2000 km along the North American West Coast. We measured in laboratory and field trials virus infection, as well as aphid vector fecundity and feeding preferences on several host species. Virus prevalence increased as local host richness declined. Grass community disassembly in this system was non-random: hosts from our ubiquitous sentinel species dominating species-poor assemblages were among the most competent for vector production and virus transmission. These results suggest that non-random biodiversity loss led to predictable increases in disease prevalence, providing a clear mechanism by which disease dilution can occur.
Community assembly processes may provide a predictive framework for understanding the mechanisms underlying disease dilution (reduced disease prevalence with increasing biodiversity). The effect of ...biodiversity on disease prevalence may depend both on a heterogeneity in host traits related to disease spread and on the order of species loss in community disassembly. If host communities decay to a predictable subset of hosts, disease prevalence may reflect the competence of the remaining hosts. To test this hypothesis, we measured local host species abundance and prevalence of four generalist aphid-vectored pathogens (barley and cereal yellow dwarf viruses, Luteoviridae) in a sentinel ubiquitous annual grass host (Bromus hordeaceus, Poaceae) at 10 sites spanning 2000 km along the North American West Coast. We measured in laboratory and field trials virus infection, as well as aphid vector fecundity and feeding preferences on several host species. Virus prevalence increased as local host richness declined. Grass community disassembly in this system was non-random: hosts from our ubiquitous sentinel species dominating species-poor assemblages were among the most competent for vector production and virus transmission. These results suggest that non-random biodiversity loss led to predictable increases in disease prevalence, providing a clear mechanism by which disease dilution can occur.
The pathogen and parasite community that inhabits every free-living organism can control host vital rates including lifespan and reproductive output. To date, however, there have been few experiments ...examining pathogen community assembly replicated at large-enough spatial scales to inform our understanding of pathogen dynamics in natural systems. Pathogen community assembly may be driven by neutral stochastic colonization and extinction events or by niche differentiation that constrains pathogen distributions to particular environmental conditions, hosts, or vectors. Here, we present results from a regionally-replicated experiment investigating the community of barley and cereal yellow dwarf viruses (B/CYDV's) in over 5000 experimentally planted individuals of six grass species along a 700 km latitudinal gradient along the Pacific coast of North America (USA) in response to experimentally manipulated nitrogen and phosphorus supplies. The composition of the virus community varied predictably among hosts and across nutrient-addition treatments, indicating niche differentiation among virus species. There were some concordant responses among the viral species. For example, the prevalence of most viral species increased consistently with perennial grass cover, leading to a 60% increase in the richness of the viral community within individual hosts (i.e., coinfection) in perennial-dominated plots. Furthermore, infection rates of the six host species in the field were highly correlated with vector preferences assessed in laboratory trials. Our results reveal the importance of niche differentiation in structuring virus assemblages. Virus species distributions reflected a combination of local host community composition, host species-specific vector preferences, and virus responses to host nutrition. In addition, our results suggest that heterogeneity among host species in their capacity to attract vectors or support pathogens between growing seasons can lead to positive covariation among virus species.
The pathogen and parasite community that inhabits every free-living organism can control host vital rates including lifespan and reproductive output. To date, however, there have been few experiments ...examining pathogen community assembly replicated at large-enough spatial scales to inform our understanding of pathogen dynamics in natural systems. Pathogen community assembly may be driven by neutral stochastic colonization and extinction events or by niche differentiation that constrains pathogen distributions to particular environmental conditions, hosts, or vectors. Here, we present results from a regionally-replicated experiment investigating the community of barley and cereal yellow dwarf viruses (B/CYDV's) in over 5000 experimentally planted individuals of six grass species along a 700 km latitudinal gradient along the Pacific coast of North America (USA) in response to experimentally manipulated nitrogen and phosphorus supplies. The composition of the virus community varied predictably among hosts and across nutrient-addition treatments, indicating niche differentiation among virus species. There were some concordant responses among the viral species. For example, the prevalence of most viral species increased consistently with perennial grass cover, leading to a 60% increase in the richness of the viral community within individual hosts (i.e., coinfection) in perennial-dominated plots. Furthermore, infection rates of the six host species in the field were highly correlated with vector preferences assessed in laboratory trials. Our results reveal the importance of niche differentiation in structuring virus assemblages. Virus species distributions reflected a combination of local host community composition, host species-specific vector preferences, and virus responses to host nutrition. In addition, our results suggest that heterogeneity among host species in their capacity to attract vectors or support pathogens between growing seasons can lead to positive covariation among virus species.
