The pattern of distribution of the two sibling species Euryrhynchus amazoniensis and E. burchelli (Decapoda, Palaemonidae) in the Central Amazonian blackwater stream Tarumã-Mirím, and the problem of coexistence

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, Euryrhynchus 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.