The Scaling of Host Density with Richness Affects the Direction, Shape, and Detectability of Diversity-Disease Relationships

<div><p>Pathogen transmission responds differently to host richness and abundance, two unique components of host diversity. However, the heated debate around whether biodiversity generally increases or decreases disease has not considered the relationships between host richness and abundance that may exist in natural systems. Here we use a multi-species model to study how the scaling of total host community abundance with species richness mediates diversity-disease relationships. For pathogens with density-dependent transmission, non-monotonic trends emerge between pathogen transmission and host richness when host community abundance saturates with richness. Further, host species identity drives high variability in pathogen transmission in depauperate communities, but this effect diminishes as host richness accumulates. Using simulation we show that high variability in low richness communities and the non-monotonic relationship observed with host community saturation may reduce the detectability of trends in empirical data. Our study emphasizes that understanding the patterns and predictability of host community composition and pathogen transmission mode will be crucial for predicting where and when specific diversity-disease relationships should occur in natural systems.</p></div

SnailShedDataforDryad

Laboratory-raised Helisoma trivolvis snails were held at one of 5 acclimation temperatures (13-25 deg C) for 11 days prior to being moved to one of 5 performance temperatures (16-28 deg C) for 7 days. Some snails were exposed in the laboratory to Ribeiroia ondatrae, and parasite release was measured at several time-points before and after the temperature shift. Please see paper methods for more details

Conceptual diagram of assembling the global host community, species traits, and local communities.

<p><i>A</i>, Preston’s octaves of abundances and resulting rank-abundance of the 49 host species used in our model. <i>B,</i> Schematic of our methods for choosing 1000 local communities. Species in local communities were chosen at random, ranging from richness of 2 to 49.</p

Results of GAM to test the effect of community abundance-richness relationships and pathogen transmission mode on community R₀-richness relationships across a range of sample sizes.

<p><i>A</i>–<i>C</i>, Proportion of simulations where the GAM was significant versus sample size, for the three treatments: <i>A</i>, “additive” method with density-dependent transmission; <i>B</i>, “additive” method with frequency-dependent transmission; and <i>C</i>, “saturating” method with density-dependent transmission. The horizontal dashed lines in <i>A–C</i> show the total proportion of significant cases across all sample sizes (i.e. out of 820 simulations) for each of the three treatments. Parameters of generated local communities follow those specified in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0097812#pone-0097812-g002" target="_blank">Figure 2</a>.</p

Parameter assignment and definitions for creating the species pool and epidemiological model.

<p>Parameter assignment and definitions for creating the species pool and epidemiological model.</p

The coefficient of variation of community R₀ at each value of richness for the simulated communities shown in Figure 2.

<p>The underlying relationships between community abundance and richness are shown as inset Figures. Parameters are as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0097812#pone-0097812-g002" target="_blank">Figure 2</a>.</p

Paull_2017_tables_figures_text_ESM from Drought and immunity determine the intensity of West Nile virus epidemics and climate change impacts

Additional tables, figures, methods and discussion detailing effects of immunity, temperature, precipitation, winter freezes and drought on human West Nile virus cases across the United State

Altman et al. 2016 JAE tadpole acclimation data

Data from the tadpole acclimation experimen

Altman et al. 2016 JAE trematode acclimation data

Data from the trematode acclimation experimen

Appendix A. Field sampling methods, rarefaction curves, and detailed information on experimental parasite additions, the final size/counts of host snails, and mesocosm water chemistry.

Field sampling methods, rarefaction curves, and detailed information on experimental parasite additions, the final size/counts of host snails, and mesocosm water chemistry