Plant-caterpillar food web: Integrating leaf stoichiometry and phylogeny

1. Trophic interactions and plant-herbivore network structure may be regulated by ecological and evolutionary factors. The allocation of resources to physical and chemical traits may influence plant nutritional values and defence against insect herbivores. However, the elemental consistency of plant leaves is rarely considered a functional trait, despite leaf chemical traits being critical for understanding trophic interactions and network modularity. 2. We constructed a high-resolution network of a plant-caterpillar food web in a subtropical forest in southern China using DNA barcoding. We analysed whether abundance, phylogeny, and functional traits (including leaf chemical elements) significantly differed among modules and conducted linear regressions to explore how these traits could explain the intensity and likelihood of trophic interactions between plants and caterpillars. 3. Caterpillar feeding intensity increased with increasing specific leaf area and leaf nitrogen to phosphorus (N:P) ratio. The intensity and likelihood of feeding decreased with increasing calcium and magnesium levels. Leaf dry matter content and leaf concentrations of potassium, magnesium, copper, and manganese varied among modules. Caterpillar feeding likelihood and intensity were constrained by plant and caterpillar phylogenies, and module phylogenetic clustering was apparent. Species abundance of plants and caterpillars constrained the feeding intensity but not the likelihood of feeding and network module composition. 4. We highlighted the combined roles of functional traits and phylogeny in shaping trophic interactions and modularity in plant-insect herbivore networks and illustrated the importance of leaf stoichiometry in establishing dietary associations.