Resumen:
To determine the effect of rivers, environmental conditions, and isolation by distance on
the distribution of species in Amazonia. Location: Brazilian Amazonia. Time period:
Current. Major taxa studied: Birds, fishes, bats, ants, termites, butterflies, ferns ? lycophytes,
gingers and palms. We compiled a unique dataset of biotic and abiotic information
from 822 plots spread over the Brazilian Amazon. We evaluated the effects of environment,
geographic distance and dispersal barriers (rivers) on assemblage composition of
animal and plant taxa using multivariate techniques and distance- and raw-data-based
regression approaches. Environmental variables (soil/water), geographic distance, and
rivers were associated with the distribution of most taxa. The wide and relatively old
Amazon River tended to determine differences in community composition for most biological
groups. Despite this association, environment and geographic distance were generally
more important than rivers in explaining the changes in species composition. The
results from multi-taxa comparisons suggest that variation in community composition in
Amazonia reflects both dispersal limitation (isolation by distance or by large rivers) and the
adaptation of species to local environmental conditions. Larger and older river barriers
influenced the distribution of species. However, in general this effect is weaker than the
effects of environmental gradients or geographical distance at broad scales in Amazonia,
but the relative importance of each of these processes varies among biological groups.