Aim: The strength of species interactions is traditionally expected to increase toward
the Equator. However, recent studies have reported opposite or inconsistent latitudinal trends in the bottom-up (plant quality) and top-down (natural enemies) forces
driving herbivory. In addition, these forces have rarely been studied together thus
limiting previous attempts to understand the effect of large-scale climatic gradients
on herbivory.
Location: Europe.
Time period: 2018–2019.
Major taxa studied: Quercus robur.
Methods: We simultaneously tested for latitudinal variation in plant–herbivore–natural enemy interactions. We further investigated the underlying climatic factors associated with variation in herbivory, leaf chemistry and attack rates in Quercus robur
across its complete latitudinal range in Europe. We quantified insect leaf damage and
the incidence of specialist herbivores as well as leaf chemistry and bird attack rates
on dummy caterpillars on 261 oak trees.
Results: Climatic factors rather than latitude per se were the best predictors of the
large-scale (geographical) variation in the incidence of gall-inducers and leaf-miners
as well as in leaf nutritional content. However, leaf damage, plant chemical defences
(leaf phenolics) and bird attack rates were not influenced by climatic factors or latitude. The incidence of leaf-miners increased with increasing concentrations of hydrolysable tannins, whereas the incidence of gall-inducers increased with increasing
leaf soluble sugar concentration and decreased with increasing leaf C : N ratios and
lignins. However, leaf traits and bird attack rates did not vary with leaf damage.
Main conclusions: These findings help to refine our understanding of the bottom-up
and top-down mechanisms driving geographical variation in plant–herbivore interactions, and indicate the need for further examination of the drivers of herbivory on
trees.