Phylogenetic relatedness of food plants reveals highest insect herbivore specialization at intermediate temperatures along a broad climatic gradient

Phytophagous insects differ in their degree of specialisation, biased by resource availability. The composition and richness of herbivore and plant assemblages change along climatic gradients, but knowledge about associated shifts in specialisation is scarce and lacks controlling for abundance and phylogeny of interaction partners. Thus, we aimed to test whether the specialisation of herbivores in insect- plant – interaction networks decreases towards cold habitats as predicted by the 'altitude niche-breadth hypothesis' to forecast possible consequences of interaction rewiring under climate change.

We used a non-invasive, standardized metabarcoding approach to reconstruct dietary relationships of Orthoptera species as a major insect herbivore taxon along a broad temperature gradient (~12 °C) in southern Germany. Based on orthopteran surveys, direct feeding observations in field, collection of faecal pellets from > 3,000 individuals of 54 species, and parallel vegetation surveys on 41 grassland sites, we quantified plant resource availability and its use by herbivores. Faecal samples were pooled for each species per site.