Cross-taxa comparative analysis of long-term community data
The increasing availability of long-term datasets through on-line resources such as the LTER Network permits new opportunities for comparative temporal analysis of ecological data. One way these can be used is to explore how ecological communities change over time in response to global environmental change. Metrics of community diversity have been used to assess how local biodiversity is changing over time. Here, we explore how species diversity and composition of plants, grasshoppers, birds, and small mammals in arid (Sevilleta LTER, New Mexico) and mesic (Konza Prairie LTER, Kansas) grasslands are changing over time. Specifically, we asked whether or not communities of different taxa at each site changed or remained the same under changing climate regimes (drought at Sevilleta) and disturbances (fire frequency at Konza). Data from Konza extend from 1982 to the present, depending on taxon. For Sevilleta data sets run from 1989 to the present.
Based on time-lag analysis, Sevilleta grassland and creosote plant communities are undergoing directional change in species composition, but surprisingly the grassland is changing at a faster rate than creosote shrubland. Grasshopper communities show the same pattern between these two sites. Small mammal and bird communities, on the other hand, show high interannual variability in composition but are not undergoing directional change. At Konza Prairie, grasshopper communities are undergoing strong directional change on sites burned annually and once every four years, but not on the unburned site. Small mammal communities are changing the least in annually burned prairie but with strong community change in unburned prairie. Based on coefficient of variation (CV), total cover of plant communities was less stable over time than total abundance of consumers under all fire frequencies. However, grasshoppers and birds had the highest CV of annual total richness under all fire frequencies. Plant communities had the lowest CV of richness for most sites. In general, 1) there is directional change in both grassland systems, 2) several consumer communities at Konza Prairie are changing rapidly, where they are more stable at Sevilleta, and 3) grassland richness is stable although the communities are undergoing directional change over time.