Performance of a tri-trophic food web under different climate change scenarios

Climate change prediction models estimate an increase in the temperature of the planet of about 2 to 5 °C by the late 21st century. This increase in temperature is very likely to have a direct impact on living organisms in terrestrial ecosystems, especially plants, and their ectotherm consumers that are already exposed to their upper thermal limits. Although the effects of temperature on the physiology, biology and behaviour of the individual components of a plant-based food web (plant, herbivore and parasitoid) have been extensively studied; the effects on the food web as a whole remain less clear. One of the main obstacles in studying multi-level food webs has been the lack of common measure to compare the performance of plants in relation with insect herbivores and parasitoids. We used biomass production rates integrated into single-metric ratios (ϕh/p and ϕ3t) to evaluate a model tri-trophic web based on a crop plant, an aphid and a parasitoid, under three climatic scenarios for the 2050 horizon. Our results show that in spite of their reduced thermal window, the parasitoids could dominate the food web in a top-down fashion under all climatic scenarios. However, in their absence, the herbivore clearly outperformed plant growth potential in biomass production, a situation that would be unsustainable in the long term. The results are discussed in the context of their ecological and agricultural implications.