For two different pioneer plant communities, the organismic concept and the individualistic concept predict that succession will lead to two different outcomes. The organismic concept predicts that both communities will converge in similarity. The individualistic concept predicts that the communities will remain distinct. To test this controversy, two dissimilar nearby habitats were selected in a small stream. The habitats contained different algal communities. Three substrate holders, each capable of holding nine frosted acrylic substrates, were placed in both habitats. After an initial two-week period of colonization, the three substrate holders from one habitat were transferred to the other so that all six were together. Substrates were collected in a geometrically increasing sequence of days, up to 64 days. T-tests on the similarity (SIMI) between the two communities indicated that they were not different immediately after the transfer. They were different on Day 1 and Day 2 after the transfer, and then they converged on Day 4 and remained indistinct for the rest of the study. Taxa mean relative abundances differed (t-tests) only before the transfer. Sign tests indicated that six taxa (Achnanthes lanceolata, Amphora perpusilla, Cocconeis diminuta, C. pediculus, Fragilaria brevistriata, and F. construens var. venter) tended to remain relatively more abundant in one community over the other. Current velocity was important in determining community composition. The prediction of the individualistic concept was supported best. The convergence may be explained by changes in stream ’climate’ and the insensitivity of SIMI to low relative abundances. The ability of taxa to remain relatively more abundant for long periods of time follows the expectations of the individualistic concept. Succession in periphyton was indicated by the decrease in SIMI between samples as the number of days between samples increased.