AimWe evaluated different facets of beta diversity (taxonomic, phylogenetic and functional), and its components (spatial turnover and nestedness), of a stream macroalgal metacommunity, as well as the effect of local environmental variables, types of biome and spatial factors on these facets and components.LocationTen natural areas of southern Brazil, covering the main biomes represented in the region.TaxonStream macroalgae.MethodsWe analysed a macroalgal data set collected in 105 stream segments using a dissimilarity partitioning approach to decompose total beta diversity into spatial turnover and nestedness components. Furthermore, we assessed the effects of local environmental variables, biome type and spatial factors on beta diversity components by performing distance‐based redundancy analysis (db‐RDA), and its partial version (db‐pRDA). Taxonomic data were tabulated considering four different species incidence matrices: total macroalgae; only green algae; only red algae and only cyanobacteria.ResultsFor taxonomic and phylogenetic facets, very high values of total beta diversity were found for all species incidence matrices, with spatial turnover (species replacement) accounting for almost all this diversity; nestedness had extremely low values. For functional diversity, total beta diversity was again high and spatial turnover was greater than nestedness, but nestedness (the tendency for less diverse locations to contain a subset of those in higher diversity locations) was considerably higher than that observed for taxonomic and phylogenetic facets. In regard to taxonomic and phylogenetic facets, total beta diversity and spatial turnover were, in general, significantly related to local environmental variables, biome type and spatial factors for total macroalgae and green algae, whereas they were significantly related to types of biome and space for red algae, and only to local environment for cyanobacteria.Main conclusionsOur results showed that spatial turnover was the main component of beta diversity, regardless of the facet and macroalgal species incidence matrix, and that the relative influence of local environmental variables, types of biome and spatial factors on the total beta diversity and its spatial turnover component can vary according to the facet considered and by algal group.

The results may provide useful information for health agencies and policymakers in focusing efforts in epidemiological hotspots. Therefore, understanding the niche distribution dynamics of Aedes aegypti is an important step towards public health planning for vector control.

Universidade Federal da Integrac ßão Latino-Americana (UNILA), Parque Tecnol ogico Itaipu, Foz do Iguac ßu, Paran a, Brasil SUMMARY 1. Habitat complexity is thought to play an important role in various ecological communities, but its role under variable natural conditions is not well understood, particularly in lotic habitats where the complexity of the substratum influences the diversity and abundance of the benthic community. 2. We investigated the effects of the habitat complexity of the substratum, as represented by fractal structure, on the establishment of stream macroalgae. We also analysed the influence of hydraulic conditions associated with variations in the fractal dimension of the substratum. We hypothesised that habitats with higher surface complexity would have higher macroalgal abundance and that hydraulic conditions would affect macroalgal establishment differently on surfaces of differing complexity. 3. We designed a field experiment to elucidate the role of habitat complexity (represented by the fractal dimension and density of roughness elements) and consequent hydraulic conditions (assessed by the Reynolds number and drag forces) on algal growth. Sterile artificial substrata with five levels of complexity were placed in four unshaded streams. After 60 days of complete submergence, the substrata were removed from the streams, and the per cent cover of macroalgae was measured. 4. We used a principal components analysis (PCA) to reduce the dimensionality and collinearity among our variables (fractal dimension, density of roughness elements, Reynolds number and drag force) and summarise them adequately. Axis 1 (PC1) values were used in a linear model to assess the relationship between the variables and macroalgal cover. 5. PC1 explained 82.2% of the variability in substratum complexity and hydraulic condition. The fractal dimension and density of the roughness elements were negatively related with PC1, whereas the Reynolds number and drag force were related positively. Hydraulic conditions differed among each level of complexity, with the Reynolds number and drag force decreasing with increasing complexity. Macroalgal cover increased on surfaces with lower turbulence and drag force, indicating that less aggressive conditions are suitable for macroalgal colonisation. Additionally, the establishment of macroalgae was greatest on the leading edge of flat-top ridges, where the water velocity slows and the current changes direction. 6. Habitat complexity and hydraulic conditions play an important role in the establishment of macroalgae in streams and could explain their naturally patchy distribution.

-The relative effects of irradiance and spectral composition on the colonization and development of macroalgal communities were examined in four streams exposed to full sunlight in southern Brazil. A set of solar filters surrounded the artificial substrata to provide various quantitative and qualitative light conditions. In addition to the control, the conditions were full sunlight attenuated by 50, 70 and 90%, blue light (filter transmitting 430-500 nm), green light (500-600 nm) and red light ( > 600 nm). Macroalgal percent cover was determined three times during the colonization period (15, 39 and 70 days). Significant differences occurred in the mean values for macroalgal community percent cover between treatments at 15 and 39 days, suggesting that early and intermediate stages of the colonization were directly influenced by irradiance. There was an almost complete absence of macroalgae with 90% attentuation, but progressive increases with 70 and 50% attenuation. However, the mean values for macroalgal community percent cover did not differ significantly between color treatments, suggesting that the effects of irradiance on macroalgal colonization were stronger than those of spectral composition at similar intensity. The quantitative responses differed among the taxa.

No abstract

Photosynthetic performance was assessed for the main groups of primary producers of low‐order tropical streams, comprising macroalgae (11 taxa of Chlorophyta, Rhodophyta and Xanthophyta plus Cyanobacteria), bryophytes (2), angiosperms (3), and the periphytic community, by means of the Chl‐a fluorescence and oxygen evolution techniques. Samples of primary producer were collected in nine stream reaches within the same drainage basin that were characterised as open or partially shaded. Low values of compensation irradiance (Ic) were found for all species tested, suggesting that they are able to maintain an autotrophic metabolism even under very low irradiances. Parameters derived from photosynthesis–irradiance curves revealed high values of the saturation parameter (Ik), associated with relative low values of photosynthetic efficiency (αETR) and photoinhibition (βETR) for species of Chlorophyta and the periphyton, suggesting adaptation to high irradiance conditions. Species of Rhodophyta, Xanthophyta, Bryophyta and angiosperms showed, in general low values of Ik and moderate to high values of αETR and βETR, indicating typical photosynthetic responses of shade‐adapted plants. Chlorophyta and the periphyton showed high photosynthetic efficiency in high irradiance, and rhodophytes, bryophytes and angiosperms seemed to be more efficient in shaded stream stretches. Considering that Cyanobacteria showed high values of the photosynthesis/respiration (P/R) ratio, we suggest that this group is the most efficient primary producer in a wide range of low‐order tropical streams. This physiological trait could be a feature that favours the abundance of Cyanobacteria in the benthic primary producer community, as is often reported in the literature.

The effects of habitat complexity have been considered important factors for the evolution of morphological complexity in organisms. We assessed the possible relationship between hydraulic niche conditions and the morphological complexity of algal filaments by sampling four species of macroalgae inhabiting different hydraulic niches in two freshwater streams. These algal species exhibit different fractal dimensions, which were measured by applying a grid method. The results showed that morphological differences are a function of hydraulic niche for stream macroalgae. Algae with complex shape (Nitella wrightii and Batrachosperum puiggarianum) were established in slower flows, while algae with simpler filament shape (Vaucheria sp. and Oedogonium sp.) were more likely to occur in faster water currents. The sites where the species occurred are a reflection of their ability to hold position, which is ultimately driven by their morphology. The influence of flow in stream habitats is an important factor for lotic macroalgae settlement and its effects can be related to evolutionary adjustment of body shape in these environments. We suggest that the morphological structure (here as fractal dimension) of freshwater macroalgae can be considered an adaptation to the costs and benefits exhibited by different hydraulic niches.

Spatial and temporal distribution of stream macroalgae in streams from southeastern Brazil were assessed for one year. The fluctuations in macroalgal species composition and environmental factors were monitored monthly. The region exhibit a tropical climate, with defined rainy and dry seasons. Nineteen species were found, with a predominance of Chlorophyta (52.7% of the species), followed by Cyanobacteria (26.3%), Ochrophyta and Rhodophyta (10.5% each). Scytonema arcangeli had the highest number of records (63.6%), while Mougeotia capucina occurred in all sampling sites. Community structure had low similarity (20-26%) and the environmental factors showed a weak contribution to the distribution pattern observed. Despite this, the light availability at the stream-bed seems to be a major influence on the macroalgal seasonal dynamics. We suggest that macroalgae communities are predominantly composed of rare species, and this could explain the lack of a clear spatial and temporal variation pattern of these organisms.