Broad-scale variation of fungal-endophyte incidence in temperate grasses

1. The strength of many interactions between plants and other organisms changes across regional gradients. For example, the relevance of plant-herbivore interactions increases with primary production. Likewise, biotic interactions collectively become more intense from the poles to the equator. Yet, the regional variation of the interaction between grasses and systemic fungal endophytes, which provide resistance to biotic and abiotic environmental factors (i.e. herbivory and drought), is poorly understood. 2. We compiled 1008 records of the incidence level of fungal endophytes (Epichloë, Ascomycetes: Clavicipitaceae) on wild populations of 48 cool season grasses, encompassing 10 biomes across a broad latitudinal expanse and primary production gradient. Symbiosis incidence was analysed as a function of mean primary production, precipitation, temperature, and latitude of each site, which in turn were obtained from climatic and satellital sources. 3. Across a 30-fold variation of mean prima...