Ontogenetic responses of four plant species to additive and interactive effects of land‐use history, canopy structure and herbivory

Abstract

Summary The strength of interactions among species is often highly variable in space and time, and a major challenge in understanding context‐dependent effects of herbivores lies in disentangling habitat‐mediated from herbivore‐mediated effects on plant performance. We conducted a landscape‐scale experiment that manipulated light availability in woodlands with either a history of agricultural use or no history of agricultural use and coupled this with performance measurements of three life stages on four perennial herbaceous species exposed to varying levels of herbivory. We found that the context‐dependent effects of herbivory on plant performance changed as plants grew: juvenile plant survival was reduced by herbivores in low‐light habitats whereas biomass of adult plants was reduced by a more diverse insect fauna in high‐light environments. A history of agricultural land use also had negative effects on seedling establishment and adult performance, independent of herbivory. Synthesis. This work experimentally separates the habitat‐mediated effects on plant performance from the herbivore‐mediated effects on plant performance and highlights how context‐dependent interactions depend on plant ontogenetic stages.