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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.

Aim Despite the accelerating loss of biodiversity and the increased number of methods for conservation planning, the availability of information about the spatial distribution of biodiversity remains limited. One way to overcome this problem is to focus on surrogate resolutions that are able to represent specieslevel data and can be efficiently measured. Surrogates are only useful if the ecological patterns detected at the species-level still hold when based on coarser taxonomic identification, and if these responses are consistent across regions. We present a comprehensive analysis using data from a large-scale evaluation of ground-dwelling ants, to evaluate the use of surrogates.Location Amazon basin.Methods The sampling design covered 13 sites in eight phytophysiognomies, which in conjunction with other environmental characteristics (altitude, soil granulometry and slope) were used to validate the ecological patterns (ability of the surrogates to reproduce the ecological responses identified for species) of coarser surrogate taxa (indicator taxa, mixed-level approach, genus and subfamily). The surrogates were evaluated for their capacity to predict variation in total species richness and composition. We also estimated the monetary and time costs, in order to evaluate the cost-effectiveness of using different surrogate levels.Results Genus was the most cost-effective surrogate: it predicted 81% of site variation in species richness, was highly correlated (r 2 = 0.76) with species composition, very highly correlated (r 2 = 0.97) with ecological patterns detected at species level and saved~40% of total project costs. The mixed-level approach, indicator taxa and subfamily were not effective in representing the species-level data.Main conclusions Genus can be used as a surrogate for species, due to its high predictive value, independent of environmental heterogeneity. Genus may be useful as a surrogate for species in other megadiverse regions, especially where savings in project costs can be applied to increase sampling effort.

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