2002: Atmospheric CO 2 as a global change driver influencing plant-animal interactions

SYNOPSIS. Plants respond to changes in atmospheric carbon dioxide. To herbivores, the decreased leaf protein contents and increased C/N ratios common to all leaves under elevated atmospheric carbon dioxide imply a reduction in food quality. In addition to these fine-scale adjustments, the abundance of C3 and C4 plants (particularly grasses) are affected by atmospheric carbon dioxide. C4 grasses currently predominate over C3 grasses in warmer climates and their distributions expand as atmospheric carbon dioxide levels decreased during glacial periods. C4 grasses are a less nutritious food resource than C3 grasses both in terms of reduced protein content and increased C/N ratios. There is an indication that as C4-dominated ecosystems expanded 6–8 Ma b.p., there were significant species-level changes in mammalian grazers. Today there is evidence that mammalian herbivores differ in their preference for C3 versus C4 food resources, although the factors contributing to these patterns are not clear. Elevated carbon dioxide levels will likely alter food quality to grazers both in terms of fine-scale (protein content, C/N ratio) and coarse-scale (C3 versus C4) changes. Atmospheric gas composition plays an important role in determining many aspects of animal and plant metabolism (Körner, 2000). Do changes in atmospher