The assemblage composition, following selective taxa removal, was examined on already colonized rocks in a North Carolina, piedmont stream. The taxa removed were either the net-spinning caddisflyCheu-matopsyche sp.or the case-building chironomidRheotanytarsus sp.. Handled rocks with no removals were the controls. Since both taxa were numerically dominant at the start of this study but occuppied different amounts of rock space, we hypothesized that the colonization dynamics following the removals would be different between the two treatments.