Documenting the effects of short-term variation in climate on organismal trophic interactions can enhance our capability to predict the impacts of climate change on the organismal community in an ecosystem.  Because desert ecosystems are highly limited by precipitation, variation of precipitation within a season may have pronounced effects on desert organisms. Observing the effects of precipitation on primary producers in desert communities and exploring the consequences for primary and secondary consumers should enhance our understanding environmental effects on desert community dynamics, and therefore our understanding of the consequences of desert climate change as predicted by global climate change models.

The Great Basin desert scrub of southeast Oregon is a relatively simple community in which organismal interactions are easier to document and understand than more complex communities. I examined the short-term effect of simulated summer rain pulses on plant foliage condition and on the correlated responses of grasshoppers in the southeast Oregon desert. I applied water on small plots periodically over 18 days in a manner that simulated summer rain showers. I compared the water content, nitrogen content, and carbon content of leaf tissue of two prevalent shrub species, Artemisia tridentata and Sarcobatus vermiculatus in watered vs. unwatered plots.  

Results/Conclusions

There was no effect of watering treatments on any of the leaf condition factors measured, though there was a significant interaction of species, date, and watering treatment as indicated by two-way repeated measures ANOVA.  Both shrub species declined in overall leaf tissue quality over the course of the study, and there were significant differences in leaf quality between species.

While the results did not support the hypothesis that watering would have short-term consequences on leaf tissue quality as food for grasshoppers, the experiment did bring to light some clear seasonal trends in leaf quality decline. This has important consequences for grasshopper development, as the local grasshopper species develop through five instars during a period that coincides with the timing of the study. The patterns of leaf tissue quality decline over a summer will help enhance our understanding of the mechanisms that drive grasshopper abundances and the subsequence consequences on the desert predators that rely on the grasshoppers as a food source. Analyzing data on grasshopper abundances collected during summer field seasons on the same study site in 2003-2008 and correlating them to year-to-year precipitation will provide clues on the consequences of those trends on grasshoppers and their predators.