Towards a mechanistic understanding of competence: a missing link in diversity–disease research

Abstract

Biodiversity loss may increase the risk of infectious disease in a phenomenon known as the dilution effect. Circumstances that increase the likelihood of disease dilution are: (i) when hosts vary in their competence, and (ii) when communities disassemble predictably, such that the least competent hosts are the most likely to go extinct. Despite the central role of competence in diversity–disease theory, we lack a clear understanding of the factors underlying competence, as well as the drivers and extent of its variation. Our perspective piece encourages a mechanistic understanding of competence and a deeper consideration of its role in diversity–disease relationships. We outline current evidence, emerging questions and future directions regarding the basis of competence, its definition and measurement, the roots of its variation and its role in the community ecology of infectious disease.

Parasite exposure and host susceptibility jointly drive the emergence of epidemics

“…Developing creative metrics for exposure and susceptibility is key. Fortunately, there is a growing menu of empirical methods that can be leveraged to quantify exposure (e.g., antibody tracking, eDNA, and radio frequency identification; Huver et al 2015, Manlove et al 2017), as well as new computational methods that can estimate susceptibility traits and additional epidemiological parameters from host data (Borremans et al 2016, Plowright et al 2016, Stewart Merrill and Johnson 2020). These mechanistic tools will be powerful for extending the exposure–susceptibility framework to systems less tractable than Daphnia .…”

The effect of host community functional traits on plant disease risk varies along an elevational gradient

“…The functional traits expressed by those species that are able to colonize and persist in a given location can, in turn, affect disease risk Johnson et al, 2013;Kirk et al, 2019). Specifically, an infected host's ability to transmit disease to uninfected hosts, a trait often referred to as host competence, is often related to fast-growing, poorly defended tissues and short lifespans (Becker and Han, 2021;Cronin et al, 2014Cronin et al, , 2010Huang et al, 2013;Johnson et al, 2012;Martin et al, 2019Martin et al, , 2016Parker and Gilbert, 2018;Stewart Merrill and Johnson, 2020;Welsh et al, 2020). Importantly, these functional trait values also underlie ecological tradeoffs related to host growth and defense, resource acquisition and allocation, and survival and reproduction (i.e., life history) (Coley et al, 1985;Herms and Mattson, 1992;Martin et al, 2016;Reich, 2014;Reich et al, 2003;Ricklefs and Wikelski, 2002;Stearns, 1992Stearns, , 1989Wright et al, 2004).…”

Biodiversity loss underlies the dilution effect of biodiversity

“…While many studies focus on measuring the diversity of host species in the context of disease, the structure of host communities can also be measured in the context of disease using characteristics of host species or host functional traits (Johnson et al ., 2013; Halliday et al ., 2019; Kirk et al ., 2019), resulting in trait‐based measures of host community competence (Stewart Merrill and Johnson, 2020). This approach, which has rapidly gained traction in disease ecology, suggests that host species that are the best able to spread diseases (i.e., the most competent hosts), often share particular suites of physiological traits (Huang et al ., 2013; Martin et al ., 2019; Becker and Han, 2020).…”