Climate change ecology has been largely dominated by ecologically and climatically abstract research. Most experimental studies focus on manipulating only one climate variable and examining the effects on one population, species, or trophic level, when in reality both climate change and ecological communities are not so simple. As a result, we know relatively little about how the dynamics of complex food webs will respond to simultaneous shifts across interacting climate variables, and especially how the elemental stoichiometry of different trophic levels will respond. To address this knowledge gap I exposed a food web consisting of two types of plants, an insect herbivore, and an arachnid predator to both warming and drought in a New England old field ecosystem using a full factorial experimental design. The goal was to determine how warming and drought, both alone and in combination, affects the elemental stoichiometry of all three trophic levels, and the overall functioning of the food web.
The interactive effects of warming and drought on plant survival, development, and C:N ratios were significantly greater than the effects of either warming or drought on their own. Neither herbivore nor predator C:N ratios were significantly affected by the shifts in plant C:N ratios. However, predator survival was strongly impacted by warming and drought both alone and in combination, and though herbivore survival was not different between treatments, herbivore reproduction was significantly affected by warming and drought together. These results suggest that plant development and nutritional content can be more severely impacted by multiple co-occurring climate stressors than lone stressors, and that arachnids may be more sensitive to climate change in all of its forms than their herbivorous prey. In contrast, herbivores, though still able to survive co-occurring climate stressors, may respond by reducing reproductive output and overall fitness. Thus all trophic levels in arthropod food webs can be heavily impacted by realistic multi-variable climate change scenarios, but in different ways. To more accurately understand what arthropod food webs will look like as climate change continues, future studies must incorporate greater ecological and climatic complexity.