Death Valley, California, is one of the hottest, driest places in the western hemisphere. Summer daytime temperatures are regularly over 50°C, and rainfall averages less than 5 cm/year. This extreme environment is home to a thriving population of Desert Woodrats (Neotoma lepida). Unlike other populations of N. lepida, the Death Valley population is completely dependent on a single species of plant, Honey mesquite (Prosopis glandulosa), for survival. Mesquite is the sole source of thermal protection, protection from predators, water, and food. Our lab has trapped woodrats in Death Valley since 2004, centered on the question: How do the woodrats survive in this extreme environment, and what strategies do they employ in order to do so? A related question we are asking is: Are there differences in fitness across our study site? Since we cannot calculate fitness directly, we are researching differences in survivorship and fecundity across our study site. We used persistence as a proxy for survivorship and found that there are significant differences across our study site. Here, I analyze characteristics of the mesquite plants that might contribute to the differences in fitness we observed: density and length of spines, overall size, palatability, water content, and toxin content.
My results indicate there is no relationship between nitrogen content, as a component of palatability, and survivorship. Contrary to my prediction that plants with higher nitrogen content will show higher survivorship, I found a weakly negative correlation between nitrogen content and survivorship. This result may be due to several factors, including: 1) a temporal mismatch in data, 2) a confounding variable, 3) nitrogen may not be limiting in this environment, or 4) the Woodrats may be supplementing their diet with insects. In the future, I will work to resolve these issues. Although I found no relationship between spine length and persistence, I found that spine density was positively correlated with survivorship on our study site, which suggests that spinier mesquite plants are able to better protect rats from predators. This research contributes to our understanding of the ecology of N.lepida living in an extreme environment, as well as our general understanding of how organisms adapt and interact in extreme environments.