Abstract
For the last 25 years the population and community ecology of the benthic fauna of the Central Amazonian
blackwater river Tarumã-Mirím has been investigated. In 1982/83 the two shrimp sibling species, Earyrhynchus amazoniensis and E. burchelli, were found to coexist in the lower course of the river. Verification of earlier data and collections in specific sites thereafter showed that, firstly: E. burchelli is dominating in the lower course; secondly: E. amazoniensis is the exclusive species in the uppermost river stretch
still within the closed-canopy inundation forest, with one exception, which is a small colony of E. burchelli
in an isolated stream, and which persists for twenty years; thirdly: E. burchelli seems to move up-river into
the middle stretch of the Tarumã-Mirím. The patterns of colonization and coexistence are discussed in
relation to non-random population behaviour and to intra- versus inter-specific competition. The combination of these mechanisms allow for a consistent theory of coexistence within same, limiting habitats, which
may explain the coexistence of the two species E. burchelli and, E. amazoniensis, and, quite generally, the
maintenance of biodiversity in communities sharing the same resources.
