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

Abstract

Quantifying the relative impact of environmental conditions and host community structure on disease is one of the greatest challenges of the 21st century, as both climate and biodiversity are changing at unprecedented rates. Both increasing temperature and shifting host communities towards more fast-paced life-history strategies are predicted to increase disease, yet their independent and interactive effects on disease in natural communities remains unknown. Here, we address this challenge by surveying foliar disease symptoms in 220, 0.5 meter-diameter herbaceous plant communities along a 1100-meter elevational gradient. We find that increasing temperature associated with lower elevation can increase disease by (1) relaxing constraints on parasite growth and reproduction, (2) determining which host species are present in a given location, and (3) strengthening the positive effect of host community pace-of-life on disease. These results provide the first field evidence, under natural conditions, that environmental gradients can alter how host community structure affects disease.

Effects of abiotic environment on invertebrate herbivory depend on plant community context in a montane grassland

“…Specifically, in this study, the most important drivers of herbivory were multiple dimensions of plant diversity, but how those dimensions of diversity impacted herbivory depended on both the abiotic conditions and on the feeding guilds of herbivores under consideration. These results support a growing body of literature suggesting that how plant communities regulate ecosystem processes may depend on characteristics of species present in those ecosystems (Lavorel & Garnier 2002;Mouillot et al 2011;Allan et al 2015;Leitão et al 2016;Funk et al 2017;Van de Peer et al 2018;Le Bagousse-Pinguet et al 2019;Heilpern et al 2020), but that abiotic factors such as temperature can override the effects of biotic factors on ecosystem processes (Cannone et al 2007;Laiolo et al 2018;Halliday et al 2021). These results therefore suggest that predicting how global change will influence herbivory may depend on complex relationships between global change drivers and the structure of plant and herbivore communities.…”

“…As observed in a previous analysis of the CBO, species richness in the small plots was highly variable (7-30 species) and increased with elevation, while temperature declined (Halliday et al 2021) (Table S1; Figure S1a).…”

“…To evaluate how plant communities influence invertebrate herbivory across environmental gradients, we surveyed 220, 0.5 m-diameter vegetation communities (i.e., small plots), that were established in four meadows along a 1101 m elevational gradient as part of the Calanda Biodiversity Observatory (CBO; Halliday et al 2021). We then recorded the identity and visually quantified the percent cover of all plant taxa in each vegetation community.…”

“…Vegetation communities in the CBO consist mostly of perennial herbs and grasses that tolerate grazing. In the CBO, mean soil, soil surface, and air temperature all strongly and consistently decreased with increasing elevation, while mean soil moisture was uncorrelated with elevation (Halliday et al 2021). Here, we report analyses using air temperature, and because soil moisture was uncorrelated with elevation, host community structure, and disease (Halliday et al 2021), and was similarly unrelated to invertebrate herbivory, this factor was omitted from analyses.…”

“…The Calanda Biodiversity Observatory (CBO) consists of five publicly owned meadows located along a 1101 m elevational gradient (648 m to 1749 m) below tree-line on the south-eastern slope of Mount Calanda (46°53′59.5″N 9°28′02.5″E) in the canton of Graubünden (Halliday et al 2021). The soil in the area is generally calcareous and has low water retention (Eggenberg & Möhl 2013;Alexander et al 2015).…”