Accelerating rates of species extinctions and disease emergence underscore the importance of understanding how changes in biodiversity affect disease outcomes. Over the past decade, a growing number of studies have reported negative correlations between host biodiversity and disease risk, prompting suggestions that biodiversity conservation could promote human and wildlife health. Yet the generality of the diversity-disease linkage remains conjectural, in part because empirical evidence of a relationship between host competence (the ability to maintain and transmit infections) and the order in which communities assemble has proven elusive. Here we integrate high-resolution field data with multi-scale experiments to show that host diversity inhibits transmission of the virulent pathogen Ribeiroia ondatrae and reduces amphibian disease as a result of consistent linkages among species richness, host composition and community competence. Surveys of 345 wetlands indicated that community composition changed nonrandomly with species richness, such that highly competent hosts dominated in species-poor assemblages whereas more resistant species became progressively more common in diverse assemblages. As a result, amphibian species richness strongly moderated pathogen transmission and disease pathology among 24,215 examined hosts, with a 78.4% decline in realized transmission in richer assemblages. Laboratory and mesocosm manipulations revealed an approximately 50% decrease in pathogen transmission and host pathology across a realistic diversity gradient while controlling for host density, helping to establish mechanisms underlying the diversity-disease relationship and their consequences for host fitness. By revealing a consistent link between species richness and community competence, these findings highlight the influence of biodiversity on infection risk and emphasize the benefit of a community-based approach to understanding infectious diseases.

Despite calls for improved responses to emerging infectious diseases in wildlife, management is seldom considered until a disease has been detected in affected populations. Reactive approaches may limit the potential for control and increase total response costs. An alternative, proactive management framework can identify immediate actions that reduce future impacts even before a disease is detected, and plan subsequent actions that are conditional on disease emergence. We identify four main obstacles to developing proactive management strategies for the newly discovered salamander pathogen Batrachochytrium salamandrivorans (Bsal). Given that uncertainty is a hallmark of wildlife disease management and that associated decisions are often complicated by multiple competing objectives, we advocate using decision analysis to create and evaluate trade-offs between proactive (pre-emergence) and reactive (post-emergence) management options. Policy makers and natural resource agency personnel can apply principles from decision analysis to improve strategies for countering emerging infectious diseases.

Summary1. Urbanization is a growing threat to ecological communities and has become a leading cause of population extirpations in a wide range of taxa. Because the effects of urbanization are often multifaceted, identifying the pathways through which changes in communities occur has remained a persistent challenge. 2. We draw upon metacommunity theory to evaluate competing explanations for the effects of urbanization, focusing on the relative importance of processes at local (e.g. abiotic and biotic characteristics) and regional (e.g. habitat connectivity and dispersal) scales. Over 4 years, we sampled 201 wetlands in the Front Range region of Colorado, which is one of the most rapidly developing areas in the USA. 3. Wetlands embedded within urban areas exhibited significantly lower taxonomic richness and diversity compared to those in agricultural or grassland areas. Relative to grassland wetlands, urban wetlands supported a 60% lower richness of amphibians and aquatic reptiles and a 33% lower richness of aquatic insects, molluscs and crayfish. These patterns were associated with changes in biotic factors (introduced fishes and bullfrogs), abiotic factors (nutrients, conductivity and vegetation) and landscape characteristics (road density and surrounding wetland area). 4. The use of an information-theoretic approach and structural equation modelling suggested that the effects of urbanization on richness were mainly driven by changes in road density. Analyses of community composition indicated that discrete communities formed along the urban systems gradient, such that actively dispersing predators associated more negatively with urban system relative to herbivores with passive dispersal. 5. Synthesis and applications. These results highlight the importance of considering both local and regional factors in addressing conservation-related challenges and underscore the benefits of linking conceptual work on metacommunity theory with applied efforts to mitigate the effects of urbanization.

A newly identified fungal pathogen, Batrachochytrium salamandrivorans(Bsal), is responsible for mass mortality events and severe population declines in European salamanders. The eastern USA has the highest diversity of salamanders in the world and the introduction of this pathogen is likely to be devastating. Although data are inevitably limited for new pathogens, disease-risk assessments use best available data to inform management decisions. Using characteristics of Bsalecology, spatial data on imports and pet trade establishments, and salamander species diversity, we identify high-risk areas with both a high likelihood of introduction and severe consequences for local salamanders. We predict that the Pacific coast, southern Appalachian Mountains and mid-Atlantic regions will have the highest relative risk from Bsal. Management of invasive pathogens becomes difficult once they are established in wildlife populations; therefore, import restrictions to limit pathogen introduction and early detection through surveillance of high-risk areas are priorities for preventing the next crisis for North American salamanders.