Schematic of three mixture experiments and observed results. In Experiment 1, bacterial cultures were mixed so that communities were comprised of equal numbers of cells. In Experiment 2, DNA was extracted from pure bacterial cultures and then mixed so that communities were comprised of equal amounts of DNA. In Experiment 3, DNA was extracted from pure bacterial cultures and subjected to PCR and PCR product was mixed so that communities are comprised of equal amounts of PCR product. The pie charts in the bottom row are the observed results for a sample that consisted of equal proportions of seven bacteria for each experiment. The pie charts in the other rows represent the prescribed mixing ratios (each slice is of equal size). Key: red - G. vaginalis, orange - S. agalactiae, purple - S. amnii,green - P. bivia, light blue - L. iners, yellow - L. crispatus, brown - A. vaginae.