Segregação de habitat por espécies de camarões em riachos de terra firme na Amazônia

Abstract

Resource partitioning is a stabilizing mechanism known to maintain species diversity in a variety of environments. Assemblages of stream shrimp species are structured by habitat features and predation. Therefore, segregation in habitat dimension could facilitate coexistence among species in shrimp assemblages even when segregation is a result of predation pressure by fish species. These ecological interactions take place on a background modulated by biogeographic features, such as connectivity among drainages. However, these generalizations are mainly based on studies undertaken in temperate regions. We investigated whether abundances of rainforest shrimp species are related to habitat dimensions, and whether habitat-abundance relationships might be mediated through fish-assemblage structure and the effect of drainages on connectivity. Multiple regressions were used to detect relationships between shrimp-abundance and habitat, and also fish composition. Kolmogorov-Smirnov tests were used to detect specialization and habitat segregation among shrimp species. An interaction model was constructed in order to test the influence of watershed on the relation between abundance of shrimp species and habitat features. We detected effects of habitat variation on densities of shrimp species, but the magnitudes of the effects were larger for some species than others. Predator composition also affected shrimp densities. Two of the three species of shrimp showed some degree of habitat specialization, but only along current-velocity, depth and pH gradients. Habitat segregation among species occurred along the current-velocity and pH gradients. Relationships between density and environmental gradients differed between watersheds for only one species and only along the pH gradient. Our findings provide evidence that rainforest-stream shrimp species respond differently to environmental gradients and this could facilitate coexistence among species. However, predation pressure seems to have a stronger effect on species densities, and consequently species segregation, than direct effects of the environmental gradients, resulting in apparent competition for these resources.