Plant defense trait measurements
We
investigated whether abiotic and biotic factors influenced intraspecific
variation in herbivory by altering the susceptibility of individual
plants to herbivore damage. We also quantified plant chemical defenses
in three common species (Polygonum macrophyllum , Saussurea
pulchra and Taraxacum mongolicum ). Among all species identified
in the study survey, these three species had the broadest latitudinal
distributions (Figure S1).
We measured the total flavonoid, saponin and tannin contents; these
compounds are widely used by plants as toxins (i.e. , flavonoids
and saponins, Treutter, 2005; Faizal & Geelen, 2013) and digestibility
reducers (i.e. , tannins, Feeny, 1968). They are also protective
against abiotic stresses; for example, flavonoids play a role in drought
resistance and UV radiation stress tolerance (Treutter, 2005). The
quantification of these defense chemicals is described inSupplementary Methods .