Many numerical tools exist for describing community structure and how that structure changes over time. Many of these approaches are univariate (species richness) or have questionable underlying ecological meaning (rank-abundance curves). In addition, patterns of aggregate structure may mask lower order dynamics in species abundances at a site over time. Rank clocks and rank abundance statistics provide a rich graphical and analytical framework for displaying and quantifying community dynamics. We used rank clocks, in which the rank order abundance for each species is plotted at each sample date in temporal clockwise direction, to display changes in species abundances and richness over time. We used mean rank shift per time and proportional species persistence to quantify changes in community structure under different experimental or empirical treatments. Rank clocks and analyses were performed on long-term data from three LTERs: fertilized and control plots at Cedar Creek, annually burned and unburned grasslands at Konza Prairie, and grassland and shrubland communities at Sevilleta. Rank clocks show that relatively constant species richness masks considerable temporal dynamics in relative species abundances. At Cedar Creek, fertilized plots initially experienced high mean rank shifts and then stabilized rapidly below those of unfertilized plots. Rank shifts were higher in unburned vs. annually burned grassland at Konza Prairie and throughout time in grassland compared to shrubland at Sevilleta. Proportional persistence showed that arid grasslands were more dynamic than mesic grasslands. We conclude that rank clocks and rank abundance statistics provide important insights into community dynamics that are hidden in traditional univariate or curve-fitting approaches.
