Data from: Environmental and spatial effects on coastal stream fishes in the Atlantic rainforest

Contemporary and historical factors influence assemblage structure. The
environmental and spatial influences acting on fish organization of
rainforest coastal streams in the Atlantic rainforest of Brazil were
examined. Fish (and functional traits such as morphology, diet, velocity
preference, body size), environmental variables (pH, water conductivity,
dissolved oxygen, temperature, stream width, flow, depth, substrate) and
altitude were measured from 59 stream reaches. Asymmetric eigenvector maps
were used to model the spatial structure considering direction of fish
movements. Elevation played an important role – fish abundance, biomass,
and richness all decrease with increasing elevation. Fish communities are
influenced by both environmental and spatial factors, but downstream
movements were shown to be more important in explaining the observed
spatial variation than were bidirectional and upstream movements. Spatial
factors, as well as environmental variables influenced by the spatial
structure, explained most of the variation in fish assemblages. The strong
spatial structuring is probably attributable to asymmetric dispersal
limitation along the altitudinal profile: dispersal is likely to be more
limiting moving upstream than downstream. These fish assemblages reflect
scale-dependent processes: at the stream reach-scale, fish respond to
local environmental filters (habitat structure, water chemistry, and food
supply), which are in turn influenced by a larger scale, namely the
altitudinal gradient expected in steep coastal mountains. Thus,
environmental drivers are not independent of spatial factors, and the
effects of local factors can be confounded across the altitudinal
gradient. These results may have implications for conservation, because
downstream reaches are often neglected in management and conservation
plans.