Climatic change alters not only animal energy balance, but also water balance, but this latter topic has received less attention. Water can be obtained through consumption of moist food and metabolism of dry food. The breakdown of carbohydrates, lipids, and proteins can produce metabolic water, but metabolism of lipids produces more water, whereas excretion of nitrogenous waste related to protein metabolism requires water losses. Here we tested the hypothesis that climatic shifts associated with urbanization influenced animal lipid demand relative to protein, due to shifts in water balance. We placed artificial diets high in lipid or protein, and either with or without supplemented water, at 16 pairs of sites along an urbanization gradient in Toledo, OH, USA.
Results/Conclusions
Lipid consumption, relative to protein, increased with urbanization and mean temperature, but water supplementation reduced the magnitude of this association. Ants were ~50% of the observed consumers. These results suggest that shifts in nutritional demand with climatic change are partially predictable from physiological first principles related to water balance and nutrient metabolism. Because ants and other arthropods play key roles in many food webs and ecosystems, increased demand for lipids with urbanization or climate change could have major consequences for ecosystem services (e.g. urban waste removal, seed predation). Overall, our results suggest that warming related to urbanization and climate change will increase animal demand for lipids, in part to maintain water balance, and this could have important implications for both animal health and ecosystem services.