Community disassembly and disease: realistic—but not randomized—biodiversity losses enhance parasite transmission

Abstract

Debates over the relationship between biodiversity and disease dynamics underscore the need for a more mechanistic understanding of how changes in host community composition influence parasite transmission. Focusing on interactions between larval amphibians and trematode parasites, we experimentally contrasted the effects of host richness and species composition to identify the individual and joint contributions of both parameters on the infection levels of three trematode species. By combining experimental approaches with field surveys from 147 ponds, we further evaluated how richness effects differed between randomized and realistic patterns of species loss (i.e. community disassembly). Our results indicated that community-level changes in infection levels were owing to host species composition, rather than richness. However, when composition patterns mirrored empirical observations along a natural assembly gradient, each added host species reduced infection success by 12–55%. No such effects occurred when assemblages were randomized. Mechanistically, these patterns were due to non-random host species assembly/disassembly: while highly competent species predominated in low diversity systems, less susceptible hosts became progressively more common as richness increased. These findings highlight the potential for combining information on host traits and assembly patterns to forecast diversity-mediated changes in multi-host disease systems.

Eutrophication, biodiversity loss, and species invasions modify the relationship between host and parasite richness during host community assembly

“…This result supports two recent studies that found that the relationship between host and parasite richness was contingent on characteristics of host and parasite communities (Johnson et al, 2016;Wood et al, 2018). Furthermore, host community assembly is linked to parasite transmission Johnson et al, 2019;Johnson, de Roode, & Fenton, 2015;Joseph, Mihaljevic, Orlofske, & Paull, 2013), and our results suggest that contingencies in the relationship between host and parasite richness during host community assembly can emerge as a consequence of changing parasite transmission.…”

“…Our manipulation of initial host diversity was intended to represent different scenarios of biodiversity loss. But not all biodiversity loss is the same, and the process of community disassembly during biodiversity loss can influence parasite transmission (Johnson et al, 2019;Joseph et al, 2013;Ostfeld & LoGiudice, 2003), potentially confounding responses to initial richness and parasite transmission during community assembly.…”

“…Our manipulation of initial host diversity was intended to represent different scenarios of biodiversity loss. But not all biodiversity loss is the same, and the process of community disassembly during biodiversity loss can influence parasite transmission (Johnson et al., 2019; Joseph et al., 2013; Ostfeld & LoGiudice, 2003), potentially confounding responses to initial richness and parasite transmission during community assembly. Our experimental design overcame this limitation by averaging richness effects across various randomly assigned compositions (Hector et al., 2011; Liu, Chen, Lyu, Sun, & Zhou, 2018; Schmid et al., 2002), resulting in no net change in parasite abundance with initial biodiversity (Halliday, Heckman, et al, 2017).…”

“…Yet, whether this relationship is robust to changes in host community structure over time remains poorly understood, because few studies have quantified the relationship as host communities assemble. Consequently, understanding how parasite communities will respond to biodiversity loss and environmental change remains an important frontier in disease ecology (Dallas, Laine, & Ovaskainen, 2019; Farrell, Stephens, Berrang‐Ford, Gittleman, & Davies, 2015; Johnson, Calhoun, Riepe, McDevitt‐Galles, & Koprivnikar, 2019; Wood et al., 2018). The purpose of this study is to explore contingencies in the relationship between host and parasite richness that may arise during host community assembly under global change.…”

Amphibian Disease Ecology: Are We Just Scratching the Surface?

“…The diversity and dynamics of a community of host species can have a significant influence on pathogen dynamics and vice versa (Becker et al 2014;Han et al 2015;Bienentreu 2019;Johnson et al 2019). Pathogen transmission and infection prevalence are influenced by diversity, density, and abundance of suitable host species (and life stages) in the affected system (Miller et al 2011;Venesky et al 2014;Brunner et al 2015;Muths et al 2020).…”