Local Thermal Extremes Shape the Nature of Herbivore Plasticity That Controls Plant Communities

Prevailing views hold that species' physiological plasticity may confer resilience to warming, but its importance varies across climatic gradients (e.g., latitude). Yet, along such gradients local species populations may experience fine-scale spatially heterogenous variation in extreme temperatures and other ecological stressors. We show that at four Cool (mean diel maximum 29.83°C) and four Warm (mean diel maximum 31.51°C) sites, interspersed as a spatial mosaic throughout a 26,200 km² area, local herbivore populations responded differently to stress from experimental warming (ambient, warmed) and predation (presence, absence). Cool and Warm site herbivore populations utilised different combinations of behavioural and physiological plasticity to cope with the dual stressors that were contingent on local temperature extremes. These unique plastic responses had divergent cascading effects on the plant community. Our results suggest that increased attention to local population variation can enhance the ability to predict the fate of natural communities under environmental change.