Functional traits drive the inter-annual differences in the diversity of benthic macroinvertebrate communities associated with agricultural ditches

Ecological research based on both species and their traits helps us understand the mechanisms structuring ecological communities. Our aim was to dismantle the effects of environmental variables measured at multiple spatial scales on the taxonomic and functional trait composition of benthic macroinvertebrate communities and to clarify the relationship between the environment and communities in high-latitude streams. Traits were combined into unique trait combinations (site-by-traits matrix), called hereafter the overall trait composition of macroinvertebrate communities, and then the matrix was decomposed into progressively smaller parts of individual traits (site-by-individual trait matrix). The effects of variables from different spatial scales on the variation in the overall trait matrix, decomposed trait matrices, and taxonomic data were analyzed using redundancy analysis and partial linear regression modeling. Our analyses indicated that: 1) the taxonomic composition of communities was more closely associated with factors measured at larger spatial scales, and the trait composition of communities was more closely associated with factors measured at smaller spatial scales, even within 1 drainage basin; 2) decomposing overall trait composition to its individual components of single traits revealed important patterns related to the potential causal factors; and 3) the abundances of organisms exhibiting different traits may be linked strongly to different environmental variables operating at different spatial scales. Our findings highlight the benefits of describing both the taxonomic and trait composition of communities when exploring the drivers of community composition. They also have direct applications in monitoring the vulnerability of high-latitude streams to future environmental changes.

Ditches are essential elements of the agricultural landscape because of their role as habitat or refuge for aquatic species, especially in homogenized and intensively cultivated areas. However, data on the biodiversity associated with agricultural ditches, and its variation over time, are underrepresented in ecological research. This study aimed at quantifying the inter‐annual changes in the alpha and beta diversity of benthic macroinvertebrate communities across five agricultural ditches in the lowland, agricultural area of the Novara Province (northwestern Italy). Benthic macroinvertebrates were always sampled in October but in two different years: 2022 and 2023, respectively. These two years differed in the climate and hydrological conditions with lower precipitations and discharge in 2022 than 2023. The alpha diversity metrics, such as taxon richness, total abundance, Ephemeroptera, Plecoptera and Trichoptera richness and abundance, and Shannon index, were significantly higher in 2023 than in 2022. Moreover, these metrics were positively correlated with the water velocity, and negatively correlated with the concentration of phosphates. Benthic macroinvertebrate communities in 2022 showed higher beta diversity compared to 2023, with significant differences in the taxonomic composition. By controlling for the season, the results here obtained demonstrate that ditch macroinvertebrate communities are responsive to temporal variability in hydrological, climate, and environmental conditions with changes in the taxonomic diversity and composition driven by water velocity and nutrient enrichment. As agricultural ditches are still poorly monitored, this study provides science‐based information and potential insights for their sustainable management.

Macroinvertebrate functional trait responses to environmental gradients and anthropogenic disturbance in arid-land streams of North Africa

Droughts are affecting an increasing number of lotic ecosystems worldwide due to the combined effects of climatic and anthropogenic pressures. Unlike naturally intermittent rivers, where the drying phase is a part of the annual flow regime, water scarcity in Alpine rivers represents a relatively recent phenomenon and, therefore, a major threat for the biodiversity of these lotic ecosystems. However, Alpine stream community response to drought is still poorly investigated. Here, we assess the recovery of macroinvertebrates in two Alpine streams after a supraseasonal drought. As water returned, a total of 10 sampling sessions were carried out, and temporal patterns in diversity, density, and taxonomic composition of benthic communities, as well as in the percentage of functional feeding groups, were investigated.We found that the resistance of invertebrate communities in Alpine streams is generally low: drought markedly reduced the diversity and density of macroinvertebrates. Conversely, our results suggest that the passive dispersal by drift from the upstream river sections seems the most probable mechanism promoting the post‐drought recovery. Nevertheless, this resilience ability appears to be stream specific and influenced by intrinsic stream characteristics, including the flow permanence and distance from the nearest upstream perennial reach. This work sheds light on the ecological consequences of droughts on macroinvertebrate communities. As flow intermittency in Alpine areas is expected to intensify under current global change scenarios, results of this study provide important information to predict changes in the taxonomic composition and diversity of macroinvertebrate communities.

Although it has been shown that the structure and taxonomic composition of macroinvertebrate communities vary depending on multiple spatial scales, multi-scale variation of community functional composition has not been examined; despite the fundamental role of this functional composition for many ecosystem processes. In this study, functional composition of macroinvertebrate communities, in terms of the relative abundances of the different functional feeding groups, was examined in two streams in Central Spain. Differences in functional composition were found at every scale, but mostly at the segment, riffle, and sample scales, as previously observed for other community characteristics. This study highlights the necessity of multiscale designs for the study of ecological patterns and processes in streams.

Salamanders are the top predators in many fishless headwater streams, and intraguild interactions among stream salamanders are well documented. However, little is known about the top-down effects of salamanders on stream food webs or how intraguild interactions mediate these effects. To investigate the effects of salamanders on macroinvertebrate communities of headwater streams, we conducted an experiment in stream mesocosms to test for effects of two stream salamander species, namely, Eurycea bislineata and Gyrinophilus porphyriticus, alone or in combination, on benthic and emerging macroinvertebrate density, biomass, and community composition. We also assessed intraguild interactions between these salamander species by comparing Eurycea bislineata survival and G. porphyriticus growth in single-species versus two-species treatments. Gyrinophilus porphyriticus reduced benthic macroinvertebrate densities when alone but not when co-occurring with E. bislineata. There were no effects of salamanders on benthic macroinvertebrate biomass or community composition and no effects on emerging macroinvertebrate density, biomass, or community composition. Eurycea bislineata survival decreased and G. porphyriticus weight increased in two-species treatments, suggesting that intraguild predation was occurring. Overall, although some of our findings are equivocal, these results suggest that salamanders can exert top-down control on macroinvertebrate communities in fishless headwater streams, decreasing benthic macroinvertebrate density. But this effect is dependent on the salamander species present, and can be removed by intraguild interactions between salamander species.

We face increasing concerns about how the local diversity of native plant communities responds to various drivers of global change, yet often lack comprehensive studies that integrate several components of diversity and the effects of both local and regional drivers of change. We analyzed changes in taxonomic, functional, and phylogenetic diversity across 2681 (semi-)permanent temperate forest understory plots surveyed and resurveyed for all vascular plants over intervals of 15-78 yr, spanning 72 regions distributed across Europe. We quantified temporal changes in these diversity indices and assessed their responses to changes in both local drivers (plot-level overstory cover, indicator values for soil nutrients) and regional shifts in macroclimate and nitrogen deposition. Overall, local changes in taxonomic, functional, and phylogenetic diversity were centered around zero, reflecting - on average - little net change in forest diversity. Observed diversity changes mostly reflected local conditions such as overstory cover change and baseline soil nutrients rather than regional drivers of large-scale change. Changes in phylogenetic diversity correlated positively with changes in taxonomic diversity but negatively with changes in functional diversity. Our findings underscore the importance of local habitat management and multifaceted diversity monitoring for effective biodiversity conservation in temperate forests.

Water or sediment? Partitioning the role of water column and sediment chemistry as drivers of macroinvertebrate communities in an austral South African stream

Tropical streams shaded by riparian forests are important components of the drainage network of a watershed, which in addition to being a source of water, has a biota that accounts for the processing of organic matter of allochthonous origin. Among the organisms that occur in this system, benthic macroinvertebrates deserve to be highlighted for their taxonomic diversity and variety of ecological functions. Benthic macroinvertebrates (aquatic insects, molluscs, crustaceans and worms) have dimensions larger than 0.2 mm and are found living between or on substrates (leaf litter, macrophytes, rocks, gravels and sand). These invertebrates participate in the degradation of organic matter, facilitating the role of decomposers and acting as a link between leaf debris and higher trophic levels (macroconsumers and aquatic and terrestrial predators), therefore essential for the flow of energy and nutrient dynamics. Different climatic and hydrological conditions can influence the types of riparian forests, consequently the characteristics of water and the structure of benthic macroinvertebrate communities. In addition, the greater presence of some taxonomic groups (such as decapods) may generate differences in the proportions of functional trophic groups (FTG). In this sense, the aim of the present study was to compare the taxonomic and trophic functional structure of the benthic macroinvertebrate community of tropical inland forest streams (Central region of Brazil) with coastal forest streams (Coastal region, São Paulo), in the rainy and dry seasons, in order to test the hypotheses that inland forest streams present greater variation in taxonomic structure (composition , abundance, richness and diversity) of benthic macroinvertebrate communities between the dry and rainy seasons, in relation to the coast and that inland forest streams and coast have different proportions of FTG, due to the presence of decapods. For this, two seasonal collections were carried out in the dry and rainy seasons in three inland streams and three coastal streams. In each stream, physical and chemical parameters of water, structural characteristics of the streams, canopy cover and substrate type were measured. Samples from macroinvertebrate communities obtained, and individuals identified up to the lowest possible taxonomic level (family) and classified into functional trophic groups. Seasonality influence recorded on OD concentration, pH, turbidity, water speed, canopy %, substrate % and on the structure of macroinvertebrate communities. There was no difference in taxonomic richness between seasons, however, abundance varied between rain and drought in both locals. The inland area had greater variation in the mean abundance of benthic macroinvertebrates than coastal ones. The diversity varied between seasons in both areas, presenting higher rates in the rainy season. Among the most contributory families for dissimilarity between seasons and between areas are Chironomidae, Leptophlebiidae, Sericostomatidae, Hydropsychidae, Atyidae and Palaemonidae (the latter two being found only on the coast). The catador-collector FTG was the most abundant in both study areas. Nevertheless, the classification of FTG showed differences between the areas (inland and coast), 81.45% and 55.75% of collectors, 2.83% and 8.99% of fragmenters, 5.93% and 2.02% of predators and 0.60% and 2.21% of scrapers, respectively. Thus, spatial factors seem to directly influence the proportion of FTG, corroborating the second hypothesis of this study. On the other hand, both spatial and temporal factors can significantly influence the abundance and diversity of macroinvertebrates, but little in richness. The dominanic of macroinvertebrates belonging to the group of collector scavers indicates the presence of fine debris and the importance of this food resource in tropical streams. In addition, the fragmenters were most abundant, suggesting that the presence of this group may not be as rare in streams of tropical forests. However, the classification of FTG particularly shrimps may be inconclusive, as the contribution to leaf debris fragmentation may vary among species of the family Atyidae. In general, the high representativeness of these macroconsumers in the system may have influenced the proportion of FTG.

Community composition and diversity can change following exotic invasion. We tested the extent to which acid seep spring communities in southern Illinois had changed in composition and community heterogeneity based on three species surveys over 49 years. We also investigated the extent of changes in taxonomic and phylogenetic diversity since the invasion of Microstegium vimineum, an exotic grass. Floristic surveys of ten acid seep springs in southern Illinois were conducted in summer 2017 and compared to two previous surveys from 1968 and 2008. We investigated changes among acid seep springs and between surveys in species composition and community heterogeneity with multivariate ordination based on site dissimilarity, and univariate analyses comparing changes in taxonomic diversity (species richness and exotic species richness) and phylogenetic diversity [net relatedness (NRI) and nearest taxon indices (NTI)] determined from a species phylogeny based upon two plastid sequences (rbcL and matK). Acid seep spring communities became more compositionally similar to each other following woody plant encroachment and M. vimineum invasion. Total species richness declines were observed between surveys while exotic species richness increased. While NRI did not exhibit any temporal patterns, NTI significantly increased over time indicating that a decrease in phylogenetic diversity accompanied exotic invasion over almost half a century within these plant communities.

Headwater streams are highly heterogenous and characterized by a sequence of riffles and pools, which are identified as distinct habitats. That higher species richness and density in riffles than in pools is considered a general pattern for macroinvertebrates. As temperate winters can last long up to half a year, however, macroinvertebrate communities of riffles and pools may assemble differently under ices or snows. Particularly, defoliation concentrating in autumn can largely change habitats in both riffles and pools by litter patching. According to the absence or presence of litter patches, there exist four types of subhabitats, i.e., riffle stones, riffle litters, and pool sediments, pool litters, which are selectively colonized by macroinvertebrates. To study the spatial pattern and temporal dynamics of colonization, macroinvertebrates were surveyed in a warmer temperate forest headwater stream in Northeast China during four periods: autumn, pre-freezing, freezing, and thawing periods. Our study focused on functional trait composition, functional diversity and functional redundancy of macroinvertebrate communities. The colonization of macroinvertebrates was found to be significantly different in these subhabitats. Riffle stones supported higher taxonomic and functional diversities than pool sediments; litter patches supported higher total macroinvertebrate abundance and higher functional redundancy than riffle stones or pool sediments. The functional trait composition changed significantly with seasonal freeze-thaw in both riffle stones and pool sediments, but not in litter patches. Macroinvertebrate community in litter patches showed seasonal stability in taxonomic and functional diversities and functional redundancy. Thus, this study strongly highlights that litter patches play an important role structuring macroinvertebrate community over winter, supporting high abundance and maintaining functional stability.

Benthic invertebrate and microbial biodiversity in sub-tropical urban rivers: Correlations with environmental variables and emerging chemicals

The main goals of this study were: 1) to evaluate the structure, diversity, and functional trophic group composition of benthic macroinvertebrate communities; 2) to characterize water quality in the headwaters of the Doce river watershed, based on physical, chemical, and biological parameters (benthic macroinvertebrates, fecal coliforms, heterotrophic bacteria, and yeasts); and 3) to contribute to the knowledge of the structure and function of longitudinal gradients in lotic ecosystems in Brazil. A total of 60 benthic macroinvertebrate taxa were identified, the dominant group being the aquatic insects, with 50 families distributed in 8 orders. The dry period presented higher values of taxonomic richness and total density of benthic macroinvertebrates. A decreasing gradient was observed in these variable values from the 3rd order stretch down to the 6th order stretch. The highest Shannon-Wiener diversity values were found in the rainy period in the 3rd order stretches, which presented well-developed riparian forest. Besides the 3rd order stretches, the Pielou evenness index values were also high in the 6th order stretch. The collectors, together with the scrapers, predominated in the benthic macroinvertebrate communities in all river stretches, except in the 2nd, 4th, and 5th order stretches in the rainy period, where communities were dominated by filterers. The shredders and predators presented low densities for all river stretches. All microbiological variables presented low levels. Due to the high counts of heterotrophic bacteria and coliforms, the studied river stretches presented inadequate potability but adequate balneability levels. The results suggest that the structure, diversity, and composition of the benthic macroinvertebrate communities are influenced by the trophic resource availability, seasonality, and sediment heterogeneity. The microbiological results of this study allow inferring that the waters from Serra do Cipó have excellent potential for recreational use and as future sources of water for human consumption.

Cao et al. (2001) have recently published an assessment of the place of rare species in multivariate analyses associated with bioassessment. This assessment follows their earlier comments on this subject (Cao et al. 1998, Cao and Williams 1999) and criticism of their viewpoint (Marchant 1999). In their earlier comments Cao et al. (1998) claimed that elimination of rare species from data sets unduly biases the similarity measures used in multivariate analyses of community composition and results in an ‘‘unacceptable loss of ecological information’’. Marchant (1999) refuted this claim by noting that when rare taxa are eliminated from data sets the trends displayed by multivariate analyses are unaltered and that benthic data sets, both from freshwater and marine habitats, commonly contain much redundant information. If, as Cao et al. (1998) claimed, rare species are vital for multivariate analysis, then logically the less rare species and the common species must also be vital. In other words, all species are vital and, as Marchant (1999) noted, this amounts to saying that no redundancy exists. Such a claim is contrary to common experience. Cao et al. (2001) admitted that rare species may not be important when environmental gradients are strong. However, they suggested that rare species respond to different gradients, perhaps less important and subtle ones or those related to human impacts. They provided little evidence from the literature that such situations exist but they quoted a paper by Faith and Norris (1989) as supporting this view. Faith and Norris (1989) reanalyzed a study conducted in the La Trobe catchment of eastern Victoria, Australia (Metzeling et al. 1984, Marchant et al. 1985). Using all 269 taxa (mostly at genus or species level) Faith and Norris (1989) compared ordinations with and without rare taxa, as well as ordinations based solely on rare taxa (those with total abundances ,0.5% of the total abundance of all taxa). They showed that inclusion of rare taxa resulted in a greater number of sig-

Evidence of freshwater biodiversity decline, species extinction and severe alterations in the biological structure and function of freshwater ecosystems is accumulating. Here we explore the role of macrophyte diversity in lowland streams for the abundance, taxon richness and composition of macroinvertebrate communities also including the abundance of different functional feeding groups. We applied a controlled in situ experiment in four small lowland stream reaches situated in rural landscapes in Denmark. We were able to explain a major fraction of the variability in the macroinvertebrate communities by differences in total macrophyte surface areas among treatments, but the number of macrophyte species in the experimental treatment also played a highly significant role (i.e. one, two or three plant species) for both the abundance, richness and composition of the macroinvertebrate community. We strongly encourage managers to protect plant diversity in streams, not only because the plants themselves constitute an important part of the biodiversity, but also because they positively affect the macroinvertebrate community. Moreover, macrophyte-friendly management can be seen as a nature-based solution to mitigate the degraded physical conditions characterising many streams in agricultural catchments.