Effects of Elevated CO2 on Keystone Herbivores in Modern Arctic Ecosystems

Abstract

Elevated atmospheric CO2 generally decreases plant quality (i.e., lower protein, increase fiber) especially of C3 plants like those that dominate arctic ecosystems. Predicting how changes in the quality and distribution of plants will affect higher trophic levels in arctic ecosystems requires knowledge of the reciprocal interactions between keystone herbivores and their food plants. We review contemporary studies of one group of keystone herbivores in arctic ecosystems, arctic-nesting geese, and their response to changes in plant quality. Arctic-nesting geese are good indicators of the health of arctic ecosystems because the ecological limitations associated with being an avian herbivore require them to sensitively respond to changes in plant quality and quantity. Field studies have demonstrated that goslings that grow up in areas with poor habitat quality are smaller as adults and have reduced survival and fitness compared to geese in good quality habitat. Recent captive-rearing experiments with goslings have elucidated some of the important mechanisms that cause reduced survival, size, and fitness of geese raised on poor quality forage. This recent work emphasizes the importance of digestive constraints in determining the lowest quality of food eaten by such herbivores. Thus, predicting the effects of elevated atmospheric CO2 on arctic ecosystems requires an understanding of phenotypic flexibility in the digestive system of keystone herbivores.