Stream biodiversity and monitoring in North Central, Nigeria: the use of macroinvertebrate indicator species as surrogates

Indicator species (IS) have been employed in modern aquatic research for monitoring of environmental changes and evaluating the efficiency of environmental management procedures. In this study, we evaluated the possibility of developing surrogate indicator groups as tools for the conservation and management of the biodiversity of Northern Nigeria streams by surveying 15 streams in Niger state for benthic macroinvertebrates and environmental variables as data sets, over a period of 24 months (2016 and 2017). Samples were collected in two locations of reference and impacted sites for each of the streams surveyed. The statistically significant (P < 0.05; based on 1000 permutations) indicator species for each of the status classes (reference versus impacted) was identified using the indicator species analysis/indicator value (Indval) method. Canonical correspondence analysis (CCA) was used to evaluate the IS-environment relationships. Indicator value found fifteen species for the reference streams including Ephemeropteran (Bugilliesia sp., Tricorythus sp., Thraulus sp., Crassabwa sp.) and the Tricopteran (Leptonema sp.). Opposite, the Indval found seven (7) indicator species for the impacted streams, which included the Dipteran (Pentaneura sp., Tabanus sp.). Multivariate analysis revealed that species assemblage had wide dispersal patterns in relation to the sites for both status classes. CCA revealed that the reference and impacted indicator species responded to entirely different environmental factors, indicating their preference to particular environmental variables along the ecological gradients. While the indicator species of reference sites were associated with environmental predictors of good water quality such as high DO, increased flow, low conductivity, and low BOD, the indicator species of impacted sites were strongly related to environmental predictors of anthropogenic pollution, including low DO, high BOD, and increased nutrients concentrations. This study has provided a reference point and effective tool to monitor environmental changes, community, and ecosystem dynamics across the Northern Nigeria streams.

How Habitat Filtering Can Affect Taxonomic and Functional Composition of Aquatic Insect Communities in Small Amazonian Streams

Responses in taxonomic and functional composition of communities were analysed in small Amazonian streams at the small and large scale (habitat patches, river segment scale, and catchment scale). We hypothesised that similar responses in community structure to local environmental factors were a correlation between taxonomic and functional composition. To evaluate the response of taxonomic composition to environmental variables, redundancy analysis (RDA) and RLQ analysis were performed to investigate the response of community abundance (L) as a function of the environment (R) and traits (Q). The fourth-corner analysis was applied to summarize specific interactions between environmental variables and traits. Then, community taxonomic composition was associated with models at multiple scales of habitat (i.e. riparian/channel, substrates, and water variables). Likewise, the fourth-corner tests and RLQ axes showed associations between trait composition and environmental variables related to variables, such as riparian cover and channel morphology followed by variation in substrate size and composition. Unexpectedly, these results did not show specific associations between unique environmental variables and traits. At last, results showed that local conditions of stream habitat regulated community structure and functional composition of aquatic insects. Thus, these findings indicate that the local environmental filtering appears to be strongly associated with selected species traits adapted to occur in a range of habitat conditions. Despite the low number of analysed streams, these results provide important information for understanding the simultaneous variation in functional trait composition and community composition of aquatic insect assemblages.

Seasonal shifts in the assembly dynamics of benthic macroinvertebrate and diatom communities in a subtropical river

Identifying seasonal shifts in community assembly for multiple biological groups is important to help enhance our understanding of their ecological dynamics. However, such knowledge on lotic assemblages is still limited. In this study, we used biological traits and functional diversity indices in association with null model analyses to detect seasonal shifts in the community assembly mechanisms of lotic macroinvertebrates and diatoms in an unregulated subtropical river in China. We found that functional composition and functional diversity (FRic, FEve, FDis, MNN, and SDNN) showed seasonal variation for macroinvertebrate and diatom assemblages. Null models suggested that environmental filtering, competitive exclusion, and neutral process were all important community assembly mechanisms for both biological groups. However, environmental filtering had a stronger effect on spring macroinvertebrate assemblages than autumn assemblages, but the effect on diatom assemblages was the same in both seasons. Moreover, macroinvertebrate and diatom assemblages were shaped by different environmental factors. Macroinvertebrates were filtered mainly by substrate types, velocity, and CODMn, while diatoms were mainly shaped by altitude, substrate types, and water quality. Therefore, our study showed (a) that different biological assemblages in a river system presented similarities and differences in community assembly mechanisms, (b) that multiple processes play important roles in maintaining benthic community structure, and (c) that these patterns and underlying mechanisms are seasonally variable. Thus, we highlight the importance of exploring the community assembly mechanisms of multiple biological groups, especially in different seasons, as this is crucial to improve the understanding of river community changes and their responses to environmental degradation.

Species Pool Functional Diversity Plays a Hidden Role in Generating β-Diversity

Functional trait diversity is used as a way to infer mechanistic processes that drive community assembly. While functional diversity within communities is often viewed as a response variable, here we present and test a framework for how functional diversity among taxa in the regional species pool drives the assembly of communities among habitats. We predicted that species pool functional diversity should work with environmental heterogeneity to drive β-diversity. We tested these predictions by modeling empirical patterns in invertebrate communities from 570 streams in 52 watersheds. Our analysis of the field data provided strong support for the inclusion of both functional diversity and environmental heterogeneity in the models, and our predictions were supported when the community was analyzed all together. However, analyses within individual functional feeding guilds revealed strong context dependency in the relative importance of functional diversity, γ-richness, and environmental heterogeneity to β-diversity. We interpret the results to mean that functional diversity can play an important role in driving β-diversity; however, within guilds the nature of interspecific interactions and species pool size complicate the relationship. Future research should test this conceptual model across different ecosystems and in experimental settings using metacommunity mesocosms to enhance our understanding of the role that functional variation plays in generating spatial biodiversity patterns.