The distribution, architecture, and foliar pest damage of ten species of Pourouma (Cecropiaceae) were investigated in a 50-ha plot of old-growth tropical rainforest in the Yasuní National Park, Ecuador. Individuals were censused and ecological and architectural data recorded along three 500 x 20 transects (totaling 203 individuals). There were difference between the species in topographic preference. additionally, in two taxa (P. bicolor and P. guianensis sepp. guaneniss var. 2) there were ontogenetic changes in topographic preference. Architectural differences between the species indicated that one species, p. minor, was more shade-tolerant than the others. The level of pest damage was frequency-dependent, the more abundant species also being most attacked. Within species, small individuals were most severely damaged by pests. Thus differences in microhabitat preferences and frequency-dependent herbivory probably both contribute to the coexistence of the studied Pourouma species in the 50-ha plot in Yasuní.