Biodiversity decreases disease through predictable changes in host community competence

Abstract

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.

Phylogenetic structure and host abundance drive disease pressure in communities

“…If increasing the number of species in a community reduces the density of competent hosts or the frequency of infected vectors, then biodiversity shows a suppressive 'dilution effect' on disease 16 . On the other hand, biodiversity may increase disease through a variety of mechanisms 15,17 .…”

Dilution effect in bovine tuberculosis: risk factors for regional disease occurrence in Africa

“…The effect of biodiversity on disease dynamics has attracted much current attention in the context of global biodiversity loss and increased emergence of infectious diseases [9][10][11][12]. In theory, changes in species richness or diversity in communities can lead to a dilution effect or amplification effect by changing the abundance of competent hosts or altering the encounter rates among competent hosts in a community [7].…”

Disease ecology across soil boundaries: effects of below-ground fungi on above-ground host–parasite interactions

“…For example, dilution effects on disease transmission are essentially density-mediated effects in which numerical changes in the relative abundance of competent hosts affect disease transmission [4]. Likewise, trait-mediated indirect effects on host quality, size and behaviour can be equally important [3,[5][6][7][8]45].…”

“…Some indirect effects are density-mediated. For example, decreases in the density of parasite-competent hosts in the presence of incompetent competitors can reduce parasite prevalence [4]. Alternatively, indirect effects can be trait-mediated, wherein changes in host quality and behaviour influence parasite replication, virulence and transmission [5,6].…”