Lau, J. A. and P. Tiffin. 2009. Elevated carbon dioxide concentrations indirectly affect plant fitness by altering plant tolerance to herbivory. Oecologia 161:401-410.
Global environmental changes, such as rising atmospheric CO2 concentrations, have a wide range of direct effects on plant physiology, growth, and fecundity. These environmental changes also can affect plants indirectly by altering interactions with other species. Therefore, the effects of global changes on a particular species may depend on the presence and abundance of other community members. We experimentally manipulated atmospheric CO2 concentration and amounts of herbivore damage (natural insect folivory and clipping to simulate browsing) to examine: (1) how herbivores mediate the effects of elevated CO2 (eCO2) on the growth and fitness of Arabidopsis thaliana and (2) how predicted changes in CO2 concentration affect plant resistance to herbivores, which influences the amount of damage plants receive, and plant tolerance of herbivory, or the fitness consequences of damage. We found no evidence that CO2 altered resistance, but plants grown in eCO2 were less tolerant of herbivory; clipping reduced aboveground biomass and fruit production by 13 and 22%, respectively, when plants were reared under eCO2, but plants fully compensated for clipping in ambient CO2 (aCO2) environments. Costs of tolerance in the form of reduced fitness of undamaged plants were detected in eCO2 but not aCO2 environments. Increased costs could reduce selection on tolerance in eCO2 environments, potentially resulting in even larger fitness effects of clipping in predicted future eCO2 conditions. Thus, environmental perturbations can indirectly affect both the ecology and evolution of plant populations by altering both the intensity of species interactions as well as the fitness consequences of those interactions.
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