Meeting Abstract
11.2 Tuesday, Jan. 4 Locusts prefer nitrogen-poor plants in overgrazed pastures CEASE, Arianne*; ELSER, James; HAO, Shuguang; KANG, Le; HARRISON, Jon; Arizona State University; Arizona State University; Institute of Zoology, Chinese Academy of Sciences; Institute of Zoology, Chinese Academy of Sciences; Arizona State University acease@asu.edu
Humans have altered the nitrogen (N) cycle on both global and local scales, enriching N by agricultural fertilization and pollution, and depleting N with land-use changes. In the Asian grasslands, steppe degradation due to livestock overgrazing allows soil erosion that leads to a decrease in organic N available to plants. These changes affect plant N content, however, the subsequent effects on primary consumers and food-webs are poorly understood. In general, herbivores are assumed to be N-limited, and high N-availability to enhance fitness. We tested the effects of different plant N levels on the performance and feeding behavior of Oedaleus asiaticus, a dominant locust of north Asian grasslands. Contrary to general predictions for herbivores, we found that N-enrichment decreased size and viability in lab and field cages. This locust preferred plants with a high carbon (C):N ratio, and N-enrichment decreased palatability of the most preferred plant (Stipa grandis). Heavily grazed fields were dominated by S. grandis that were relatively high in C:N ratio, and had high population densities of O. asiaticus. S. grandis collected from heavily grazed fields were preferred over plants from adjacent ungrazed fields. These data suggest that O. asiaticus prefer and perform optimally on a low N content diet and that over-grazing promotes outbreaks of this locust by reducing the N content of the preferred plant. These results differ dramatically from current paradigms for N effects on herbivores, suggesting that we lack understanding of herbivore physiological ecology necessary to predict effects of anthropogenic changes in N availability on food webs. This research was funded partly by ARCS to AC, NSF DEB- 0925017 to JE, and NSF DDEP to AC, JF, and JE.
