Global warming is generally predicted to increase the intensity of herbivore pressure on plants. Support for this prediction often comes from short-term studies, or studies conducted in controlled laboratory settings. We examined the effect of long-term experimental warming on an aphid-sagebrush interaction (Obtusicauda coweni and Artemisia tridentata) in natural field plots in the Rocky Mountains. In no year did we find support for the prediction that warming increased aphid abundance or population growth. In fact, warming decreased aphid density on sagebrush in one year, tended to decrease aphids in a second year, and had no effect in a third year. In enclosures that excluded predators, warming decreased aphid population growth by an amount consistent with observed field density differences. Warming increased sagebrush carbon:nitrogen (C∶N) ratio and plant size, but there was no significant correlation between these variables and aphid growth or density. In a separate snow-manipulation experiment in unwarmed plots, the timing of snowmelt did not affect aphid density. In conclusion, warming reduced or did not affect aphid density in each of three years, but this effect could not be explained by differences in plant size, bulk C∶N ratio, predation, or snowmelt date. Our results suggest that long-term studies within a natural community context may provide counterexamples to the prediction that warming will increase herbivore pressure on plants.
You have requested a machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Neither BioOne nor the owners and publishers of the content make, and they explicitly disclaim, any express or implied representations or warranties of any kind, including, without limitation, representations and warranties as to the functionality of the translation feature or the accuracy or completeness of the translations.
Translations are not retained in our system. Your use of this feature and the translations is subject to all use restrictions contained in the Terms and Conditions of Use of the BioOne website.
Vol. 80 • No. 2