PARENT SESSION
Poster Session #29: Animal Population and Community Ecology.
Wednesday, August 8, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

A novel method for quatifying changes in food webs over time.

Edwards, Melanie¹, Turner, Thomas¹, Sharp, Zachary¹, ¹

ABSTRACT- Like most rivers in the US, the Rio Grande has been severely altered by river regulation facilities that may have affected the river food web. Stable isotopes can be extremely useful for quantifying changes in food webs. In order to use stable isotopes to observe changes in food webs over time, past studies have compared undisturbed reference systems to disturbed systems. In many cases, as with the Rio Grande, an undisturbed reference system does not exist. Instead, we propose using museum-preserved specimens (pre-disturbance) to compare with recently collected specimens (post-disturbance), from the same system, for stable isotope analysis. Though formalin preservation is known to change the stable isotope content of preserved tissues, our goal in this study was to determine the severity and direction of these changes caused by formalin. Our study demonstrates that the differences in the stable isotope content between fresh and preserved tissues for nitrogen, carbon, and sulfur are minimal (0.5 to 2 parts per thousand) and predictable. Several factors were investigated as potential causes for the shift in the delta values for preserved tissue (lipid extraction by formalin, differences in formalins, time in formalin, and others) in an effort to develop a correction factor. The results of this study indicate that in many cases, stable isotope analysis of museum specimens is possible. This technique will allow researchers to develop a timeline of change in food webs.

KEY WORDS: food webs, disturbance, stable isotopes