Substrate roughness affects stream benthic algal diversity, assemblage composition, and nestedness

Abstract

Heterogeneity generated by irregularities on the surface of streambed substrates is an important determinant of local species diversity of algae. However, few investigators have examined the effects of substrate roughness on the composition of algal growth forms and on patterns of species distribution. We examined the influence of substrate roughness on stream benthic algal assemblages through a field experiment with 2 treatments (smooth and rough artificial substrates for algal colonization). We assessed whether species richness, density, and assemblage composition of benthic algae (all taxa and those in 5 growth-form groups) differed between treatments and whether differences in species composition between substrates were the result of species turnover or nestedness. We also used a data subsampling procedure to investigate the effect of differences in species richness between treatments. Total species richness was higher on rough than on smooth substrates, but density did not differ between treatments. Species richness, density, and composition of the adnate/prostrate growth form did not differ between treatments. The erect/stalked growth form had higher species richness on rough substrates, but did not differ in density between treatments. All other growth forms (filamentous, motile, and metaphyton) had higher species richness and density on rough substrates and differed in species composition between substrates. The results of the subsampling analysis indicated that assemblage composition was affected by differences in species richness and by changes in species composition (i.e., turnover). Species distribution had a nested pattern, in which the assemblages on smooth substrates were a subgroup of the species occurring on rough substrates. We suggest that the differences in assemblage composition between smooth and rough substrates resulted from variability in species' capabilities to colonize substrates with or without crevices. This variability resulted in both nestedness and turnover.

Changes in Coastal Benthic Algae Succession Trajectories and Assemblages Under Contrasting Nutrient and Grazer Loads

“…Microstructures play a crucial role in diatom attachment (e.g. Wu et al 2013), which consequently alter the benthic assemblage composition at later successional stages (Schneck et al 2011). Accordingly, in our study we observed strong substrate specific differences, with Cocconeis dominating in the smoother microsubstrate surfaces, where its firmly attachment mode presents a greater resistance to the drag forces of the flow (Gari and Corigliano 2007).…”

Structure of bird communities in eucalyptus plantations: nestedness as a pattern of species distribution

“…Then, nestedness was calculated for each observed matrix and for 10 random matrices generated by each null model to obtain two sets of 10 pairs of nestedness values (the observed value and its respective value in each null model). A paired t-test was performed for each null model to test if the observed nestedness was larger than expected (Schneck et al, 2011), using the R environment (R Development Core Team, 2012).…”

Patterns in species and functional dissimilarity: insights from periphytic algae in subtropical floodplain lakes

“…Here, instead of comparing each observed value to the distribution of the simulated functional dissimilarity separately for all the 276 pairwise comparisons, we opted to conduct a paired t test so that the results would highlight the pattern for the complete dataset and not for each pairwise comparison separately. A similar approach was used by Schneck et al (2011b) and by Both & Melo (2015) for other randomization tests.…”

“…For instance, studies that analyzed different aspects related to algal biological traits showed that algal life form, adherence, and locomotion are key traits that determine algae response to light (Lange et al, 2011), nutrients (Passy, 2007;Piggott et al, 2012), sediment deposition (Piggott et al, 2012), disturbance (Passy, 2007;Schneck & Melo, 2012), substrate roughness (Schneck et al, 2011b), and dispersal patterns (Wetzel et al, 2012). In this sense, it is important to understand not only the patterns regarding the dissimilarity in species composition but also the patterns associated with functional dissimilarity.…”