LEARNING FROM THE PAST: ANCIENT PACKRAT MIDDENS PROVIDE NOVEL INSIGHTS INTO GLOBAL CHANGE ECOLOGY
Katie M. Becklin1 and Joy K. Ward
Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS
Global conditions are rapidly changing, which raises critical questions about ecosystems responses to environmental conditions. Examining global change events that occurred in the geologic past is critical for (1) establishing a baseline for how ecosystems functioned prior to anthropogenic forcing, (2) assessing potential evolutionary responses to global change, and (3) characterizing mechanisms that underlie shifts ecological communities. Ancient packrat middens, nests that preserve plant and animal specimens from the last glacial maximum (~20 kya), are invaluable in this context since they allow for comparisons of natural ecosystems across geologic timescales. The University of Kansas houses one of most extensive collections of packrat middens with over 300 specimens from across western North America. Here, we used specimens preserved within packrat middens to assess linkages between shifts in: (1) resource availability from glacial to modern times, (2) plant physiology, and (3) plant community composition and species interactions. We used a combination of stable isotope analysis, conceptual modeling, and community ecology techniques to address these questions. Our results indicate that nitrogen availability decreased from glacial to modern times in parts of the southwestern U.S. In combination with changes in atmospheric [CO2] and precipitation, these shifts in resource availability likely impacted plant physiology. In particular, our results indicate that plants decreased stomatal conductance and/or photosynthetic capacity from glacial to modern times. Plant families differed in the timing and magnitude of these physiological responses. Additionally, plant physiological responses were more similar within plant families than within co-occurring species assemblages. This suggests that plant evolutionary history may drive physiological adaptation to global change, and that shifts in leaf physiology may not be the main determinant of changes in plant community composition. Overall, this work highlights how examining the past provides novel insights into global change ecology, and ultimately enhances our ability to describe and predict ecosystem responses to current and future conditions.