Shifts in plant nutrient content in combined warming and drought scenarios may alter reproductive fitness across trophic levels

Ecological effects of climate change are difficult to predict because climate change is a multi‐variable phenomenon that can impact ecosystems through diverse pathways. Despite this fact, climate change ecology research has been dominated by relatively simplistic experiments and models. To test the importance of assessing more realistic climate and ecological scenarios an experiment was conducted to assess the interactive effects of multiple climate change variables (warming, drought) on survival and reproductive fitness across three trophic levels within a well‐studied terrestrial food web. The effects of warming and drought on the nutrient content of plants and how such changes may affect consumers was also examined. Results showed that warming and drought in combination can significantly alter the nutrient profiles of plants relative to climate variables in isolation and that multi‐variable climate change can severely impact plant reproductive fitness. Also, consumer nutrient profiles did not shift in accordance with their resources, but reproductive fitness of grasshoppers was nonetheless severely affected by warming and drought in combination. Predator survival rates decreased by more than 45% under all climate change scenarios, highlighting the variable responses of different trophic levels. The impacts across the entire food web were likely caused by a combination of metabolic changes due to warming, dehydration, altered nutrient availability and resource quality, and behavioral shifts. The results suggest that realistic climate change scenarios could dramatically affect long‐term demographic patterns as well as food web dynamics, and that single variable studies may fail to reveal the true impacts of climate change.