Taxonomic and functional homogenisation of macroinvertebrate communities in recently intermittent Alpine watercourses

1. Mountain streams in southwestern European Alps are currently shifting from perennial to intermittent flow due to the combined effects of climate change and local anthropogenic pressures. Given that flow intermittency is a recently documented phenomenon in the Alps, only scattered studies have investigated functional and taxonomical diversity of benthic invertebrate communities in recently intermittent Alpine streams.
2. We used a hierarchical sampling design to investigate patterns in taxonomic and functional diversity of benthic invertebrate communities in 13 recently intermittent Alpine streams in north-west Italy. in April 2017, we sampled benthic communities in two reaches of each stream with different hydrological conditions: a control reach, with permanent flow; and an intermittent reach, which recently experienced non-flow periods in summer.
3. We tested for the response of taxonomic richness at multiple spatial scales by partitioning total diversity into the average richness of local communities and the richness due to variation among local communities both within and among reaches. By partitioning total diversity (γ) into its local (α) and turnover (β) components we showed a decrease in local and regional species richness both within and among reaches, whereas variation among communities was significantly lower in intermittent reaches at the reach scale only.
4. The analysis of multidimensional trait space of macroinvertebrate communities in reaches with different hydrological conditions revealed a significant reduction of functional diversity, dispersion, and evenness in intermittent reaches. There was trait overdispersion in intermittent reaches, as these hosted both typical Alpine taxa and organisms adapted to flow intermittency. In particular, we observed the replacement of taxa with aquatic respiration and those preferring medium- to fast-flowing oligotrophic waters by taxa adapted to lentic habitats, air breathing and with larval dormancy phases.
5. These results indicate that recent flow intermittency has caused drastic changes in benthic invertebrate communities in Alpine streams. Our work highlights the importance of integrating taxonomic and functional diversity to thoroughly assess the impacts of flow intermittency.

     

Land-use effects on structural and functional composition of benthic and leaf-associated macroinvertebrates in four Andean streams

The replacement of native forests by pastures takes place widely in the Andes. The effects of such land-use change on aquatic assemblages are poorly understood. We conducted a comparative analysis of the effects of forest conversion to pastures on the taxonomic, structural, and functional composition of macroinvertebrates (benthic and leaf-associated) in montane and upper montane streams (ecosystem type) of the south Ecuadorian Andes. Taxonomic composition of benthic and leaf-associated macroinvertebrates was different between ecosystem type and land use. Also, major differences in the structural and functional composition of benthic and leaf-associated macroinvertebrates were mainly promoted by land use in both ecosystem types. Forested streams showed higher diversity than pasture streams, sustaining more shredder, scraper, and predatory invertebrates. We also observed differences in the macroinvertebrate communities between benthic and leaf-bag samples. Leaf bags had lower diversity and more collector invertebrates than benthic samples. This study highlights the large effect of riparian forest conversion to pasture land on macroinvertebrate communities, and the importance of using appropriate sampling techniques to characterize aquatic assemblages. We also recommend the maintenance and restoration of riparian vegetation to mitigate the effects of deforestation on stream communities and ecosystem processes.     

Scale-dependent effects of land use on plant species richness of mountain grassland in the European Alps

Traditionally managed mountain grasslands in the Alps are species‐rich ecosystems that developed during centuries of livestock grazing. However, changes in land use including fertilisation of well accessible pastures and gradual abandonment of remote sites are increasingly threatening this diversity. In five regions of the Swiss and French Alps we assessed the relationship between land use, soil resource availability, cover of the unpalatable species Veratrum album, species richness and vegetation composition of mountain grasslands across four spatial scales ranging from 1 to 1000 m². Mean species richness and the increase in the number of species with increasing area were lower in intensively grazed, fertilised pastures than in traditional pastures or in abandoned pastures. Species composition of abandoned pastures differed from that of the other management types. Plant species richness was influenced by different factors at different spatial scales. At the 1 m² scale, plant species richness was negatively related to soil nitrate and influenced by the cover of V. album, depending on land use: species richness and cover of V. album were negatively correlated in abandoned pastures, but positively correlated in fertilised grasslands. At the 1000 m² scale, a negative effect of fertilization on richness was evident. These results indicate that at small scales species richness in mountain grasslands is determined by competition for light, which should be more important if nutrient availability is high, and by positive and negative interactions with unpalatable plants. In contrast, species richness at the large scale appears to be mainly influenced by land use. This result emphasizes the importance of studying such inter‐relationships at multiple scales. Our study further suggests that the maintenance of the traditional land use scheme is crucial for the conservation of plant species richness of mountain pastures as both intensification and abandonment changed species composition and reduced plant species diversity.     

Metacommunity structure analysis reveals nested patterns in deconstructed macroinvertebrates assemblages

1. Understanding processes driving patterns of species distribution and diversity is one of the main objectives of community ecology.
2. The aim of our study was to evaluate the spatial variation in assemblage composition of stream-dwelling macroinvertebrates and identify which factors (e.g. water quality, land cover) are the most important drivers.
3. We applied the elements of the metacommunity structure approach on a dataset of 38 communities from the Futaleufú basin in northwestern Patagonia. To better understand assemblage variation, we deconstructed our macroinvertebrate dataset into different taxonomic and trait groups. We then identified the most influential factors driving community composition using random forests.
4. We found that half of our datasets (i.e. macroinvertebrate groups) exhibited a nested structure with clumped species loss, while the other half showed a quasi-nested pattern with either clumped or stochastic species loss.
5. Overall, water quality was the most important driver of community variation, although climate, geography, and land cover were more or less relevant in particular cases. We found differences in the relative importance of the selected explanatory variables among datasets. This would suggest that different components of the macroinvertebrate community respond differently to environmental factors.
6. Our findings could be of value for conservation planning, as they suggest that preserving the most species-rich streams would, to some extent, guarantee the conservation of the entire species pool.

     

Land Use Influences Niche Size and the Assimilation of Resources by Benthic Macroinvertebrates in Tropical Headwater Streams

It is well recognized that assemblage structure of stream macroinvertebrates changes with alterations in catchment or local land use. Our objective was to understand how the trophic ecology of benthic macroinvertebrate assemblages responds to land use changes in tropical streams. We used the isotope methodology to assess how energy flow and trophic relations among macroinvertebrates were affected in environments affected by different land uses (natural cover, pasture, sugar cane plantation). Macroinvertebrates were sampled and categorized into functional feeding groups, and available trophic resources were sampled and evaluated for the isotopic composition of ¹³C and ¹⁵N along streams located in the Cerrado (neotropical savanna). Streams altered by pasture or sugar cane had wider and more overlapped trophic niches, which corresponded to more generalist feeding habits. In contrast, trophic groups in streams with native vegetation had narrower trophic niches with smaller overlaps, suggesting greater specialization. Pasture sites had greater ranges of resources exploited, indicating higher trophic diversity than sites with natural cover and sugar cane plantation. We conclude that agricultural land uses appears to alter the food base and shift macroinvertebrate assemblages towards more generalist feeding behaviors and greater overlap of the trophic niches.     

Past pasture management affects the land snail diversity in nutrient-poor calcareous grasslands

Changes in agriculture (intensification or abandonment) have resulted in a dramatical reduction of semi-natural grasslands in Central Europe in the 20th century. Recent management actions aim to restore overgrown and formerly fertilized nutrient-poor grasslands. Former land use is known to influence the present-day vegetation. Similar information is not available for animals with low dispersal ability. We investigated the effect of pasture management history over a period of 55 years on the present-day land snail diversity in 20 dry, nutrient-poor grasslands in the Swiss Jura mountains. Snails were recorded in pastures left unmanaged for 10–40 years but recently cleared from overgrowing shrubs, in pastures fertilized for 15–25 years but recently managed extensively (no fertilizer), and in pastures which have been extensively managed throughout (=control). Past shrub cover had a negative effect on the total number of snail species and the number of red-listed individuals. Former use of fertilizer reduced red-listed species and individuals and changed the snail community. Three species (Vitrina pellucida, Helicella itala and Abida secale) were found less frequently in formerly fertilized pastures than in extensive pastures. Our results show that changes in pasture use for a period of 10–40 years caused long-term alterations of the land snail fauna.     

Revealing the pathways by which agricultural land‐use affects stream fish communities in South Brazilian grasslands

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Land‐use legacy and the differential response of stream macroinvertebrates to multiple stressors studied using in situ experimental mesocosms

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Functional diversity decreases with temperature in high elevation ant fauna

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Does predator abundance influence species diversity of equilibrium macroinvertebrate assemblages in spring fens?

1. Predation may significantly control number and density of coexisting species. The effects of predation on species diversity have traditionally been tested in experiments and theoretical models of simple trophic systems. In complex natural ecosystems, however, disentangling multiple sources of variation is difficult. In groundwater-fed environments, a significant effect of predation can be expected due to the relatively stable environmental conditions; however, it has never been properly examined.
2. We analysed species diversity and total abundance of macroinvertebrate assemblages in 48 Western Carpathian spring fens, separately for whole sites and mesohabitat/season, and partitioned the effects of predation intensity from those of environmental variables in robust models using a bootstrapping technique. We verified our results by accounting for taxa resistant to predation.
3. The assumption that predation-mediated coexistence of species is the main mechanism responsible for the relatively species-rich assemblages in the Western Carpathian spring fens was not supported. However, predation may significantly influence abundance of non-predatory species and, under some conditions, it may contribute to explaining patterns in species diversity.
4. The effect of predation did not differ between the mesohabitats with different stability. However, we found higher environmental control in spring and a stronger effect of predators in autumn, which suggests that different mechanisms influence fen assemblages in different seasons.
5. Our study provides a new robust approach how to test the effect of predation on natural macroinvertebrate assemblages. The importance of predation was lower than expected in equilibrium assemblages but it may vary in time.

     

Relationships between taxonomic and functional components of diversity: implications for conservation of tropical freshwater fishes

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Lateral hydrological connectivity differentially affects the community characteristics of multiple groups of aquatic invertebrates in tropical wetland pans in South Africa

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Restoration of semi-natural grasslands,a success for phytophagous beetles (Curculionidae)

Semi-natural pastures have rich plant and animal communities of high conservation value which depend on extensive management. As the area of such land decreases, abandoned semi-natural grasslands have been restored to re-establish biodiversity. Restoration schemes, which include thinning of woody plants and reintroduction of grazing, are mainly designed according to the responses of well-studied groups (such as vascular plants and birds). Weevils (Curculionidae) are a very diverse phytophagous beetle family. Here, we evaluated the restoration success of pastures for weevils (Curculionidae), by comparing their species diversity in abandoned, restored, and continuously grazed semi-natural pastures on 24 sites in central Sweden. Weevils were sampled by sweep-netting. We recorded 3019 weevil individuals belonging to 104 species. There was no statistically significant difference in species numbers between the pasture management treatments. However, weevil species composition of abandoned pastures differed from those in restored and continuously managed pastures, but there was no significant difference in community composition between restored and continuously grazed pastures. The abandoned sites tended to be dominated by polyphagous species, whereas the grazed sites contained more monophagous and oligophagous species. The number of weevil species was positively related to understory vegetation height and connectivity to other semi-natural grasslands and negatively related to the cover of trees and shrubs in the pastures. We conclude that restoration of abandoned semi-natural pastures is a good approach to restore weevil communities. To maintain a species rich weevil community, pastures should be managed to be relatively open, but still have patches of tall field-layer vegetation. Restoration and conservation measures should primarily be targeted on regions and landscapes where a high proportion of semi-natural grassland still remains.     

Plants, insects and birds in semi-natural pastures in relation to local habitat and landscape factors

The preservation of remaining semi-natural grasslands in Europe has a high conservation priority. Previously, the effects of artificial fertilisation and grazing intensity on grassland animal and plant taxa have been extensively investigated. In contrast, little is known of the effects of tree and shrub cover within semi-natural grasslands and composition of habitats in the surrounding landscape on grassland taxa. We evaluated the effect that each of these factors has on species richness and community structure of vascular plants, butterflies, bumble bees, ground beetles, dung beetles and birds surveyed simultaneously in 31 semi-natural pastures in a farmland landscape in south-central Sweden. Partial correlation analyses showed that increasing proportion of the pasture area covered by shrubs and trees had a positive effect on species richness on most taxa. Furthermore, species richness of nectar seeking butterflies and bumble bees were negatively associated with grazing intensity as reflected by grass height. At the landscape level, species richness of all taxa decreased (butterflies and birds significantly so) with increasing proportion of urban elements in a 1-km² landscape area centred on each pasture, while the number of plant and bird species were lower in landscapes with large proportion of arable fields. Our results differed markedly depending on whether the focus was on species richness or community structure. Canonical correspondence analyses (CCA) showed that the abundance of most taxa was ordered along a gradient describing tree cover within pastures and proportion of arable fields in the landscape. However, subsets of grassland birds and vascular plants, respectively, showed markedly different distribution patterns along axis one of the CCA. In contrast to current conservation policy of semi-natural pastures in Sweden, our results strongly advise against using a single-taxon approach (i.e., grassland vascular plants) to design management and conservation actions in semi-natural pastures. Careful consideration of conservation values linked to the tree and shrub layers in grasslands should always precede decisions to remove trees and shrubs on the grounds of promoting richness of vascular plants confined to semi-natural grasslands. Finally, the importance of landscape composition for mobile organisms such as birds entails that management activities should focus on the wider countryside and not exclusively on single pastures.     

The effects of land use on environmental features and functional organization of macroinvertebrate communities in Patagonian low order streams

Benthic invertebrates, water quality variables, chlorophyll a and particulate organic matter (POM) were studied in 18 sites of mountain streams in Patagonia (Argentina) subjected to six different land uses: native forest, pine plantation, pasture, harvest forest, urban and reference urban. Three streams of each land use were studied in March 2006. Macroinvertebrates were sampled in three riffles and three pools (n = 108) and biomass of detrital fractions of POM were quantified. Overall benthic POM biomass was higher at native and harvest forest than pastures, whereas fine fraction (FPOM) was higher in harvest forest than in pastures. Regarding to autotrophic subsidies bryophytes were the only that changed consistently among uses. These differences in energy resources were correlated with changes in community attributes. Shredder richness was clearly higher at native and harvest forest than exotic pine plantations, collector gatherers density was consistently high at harvest sites, and total density was significantly higher at urban and harvest forest. Multidimensional scaling ordination based on macroinvertebrate density data showed a clear separation of forested (either native or exotic species) from riparian modified areas (pasture, urban and harvest sites). Environmental variables having explanation power on macroinvertebrate assemblages were mostly related with: detritus availability (wood and leaves biomass) and impairment (total phosphorous and % sand). These results confirm that macroinvertebrate assemblage structure in Patagonian low order streams can be altered by land use practices. Among guild structure measures, those indicators based on benthic community functional attributes, shredders richness and collectors density, resulted good candidates to assess land use impacts. On account of riparian corridor management may be critical to the distribution of benthic taxa, the maintenance of good conditions of vegetation adjacent to rivers will enhance water quality and the environment for highly endemic headwater communities of Patagonian streams.     

Dung beetle community composition affects dung turnover in subtropical US grasslands

1. An important service in many ecosystems is the turnover and degradation of dung deposited by cattle. Dung beetles are the primary group of insects responsible for dung turnover, and factors affecting their abundance and distribution thus impact dung degradation. Lands lost to grazing due to dung buildup and pasture contamination total millions of acres per year in US pastures.
2. We evaluated the structural differences in dung beetle assemblages in natural grasslands versus a managed agroecosystem in subtropical southeastern Florida (USA). We measured the direct effect of dung longevity when dung beetle fauna normally inhabiting dung pats were excluded.
3. Our results indicate dung beetle abundance, functional diversity, and species richness have a substantial impact on the rate of dung turnover in subtropical pastoral lands with ~70% of dung removed from the soil surface after three months. Functional diversity and evenness did not have a significant positive effect on dung removal in managed, versus natural grasslands demonstrating a strong relationship between dung beetle assemblage composition and delivery of a key ecological process, dung degradation.
4. We suggest the importance of trees, which provide a thermal refuge for beetles, should be dispersed within matrixes of open pasture areas and within proximity to adjacent closed‐canopy hammocks to facilitate the exchange of dung beetles between habitats and therefore maintain the provisioning of dung degradation services by dung beetle assemblages.

     

Stream invertebrate diversity reduces with invasion of river banks by non‐native plants

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Drivers of diversity and community structure of bees in an agroecological region of Zimbabwe

1. Worldwide bees provide an important ecosystem service of plant pollination. Climate change and land‐use changes are among drivers threatening bee survival with mounting evidence of species decline and extinction. In developing countries, rural areas constitute a significant proportion of the country''s land, but information is lacking on how different habitat types and weather patterns in these areas influence bee populations.
2. This study investigated how weather variables and habitat‐related factors influence the abundance, diversity, and distribution of bees across seasons in a farming rural area of Zimbabwe. Bees were systematically sampled in five habitat types (natural woodlots, pastures, homesteads, fields, and gardens) recording ground cover, grass height, flower abundance and types, tree abundance and recorded elevation, temperature, light intensity, wind speed, wind direction, and humidity. Zero‐inflated models, censored regression models, and PCAs were used to understand the influence of explanatory variables on bee community composition, abundance, and diversity.
3. Bee abundance was positively influenced by the number of plant species in flower (p < .0001). Bee abundance increased with increasing temperatures up to 28.5°C, but beyond this, temperature was negatively associated with bee abundance. Increasing wind speeds marginally decreased probability of finding bees.
4. Bee diversity was highest in fields, homesteads, and natural woodlots compared with other habitats, and the contributions of the genus Apis were disproportionately high across all habitats. The genus Megachile was mostly associated with homesteads, while Nomia was associated with grasslands.
5. Synthesis and applications. Our study suggests that some bee species could become more proliferous in certain habitats, thus compromising diversity and consequently ecosystem services. These results highlight the importance of setting aside bee‐friendly habitats that can be refuge sites for species susceptible to land‐use changes.

     

Conservation and restoration of Nardus grasslands in the Swiss northern Alps

Aim: Species‐rich Nardus grasslands are high nature‐value habitats. In Switzerland, many of these grasslands are degraded even though they have been under protection since the 1980s. Degradation shows two divergent trends: Nardus grasslands are either dominated by Nardus stricta or by eutrophic plants, both trends leading to the disappearance of typical Nardus grassland species. With this study, we aim to identify the factors that could be adjusted to conserve the integrity of this habitat. Location: Bernese Alps, Switzerland. Methods: In 2016, we investigated the underlying causes of this degradation process by assessing vegetation composition in 48 Nardus grasslands located in the Swiss northern Alps of canton Bern and linking it to soil, management and environmental variables. To explore the effect of the degradation on higher trophic levels, orthopteran species richness and densities were assessed. Results: Results show that Nardus meadows (mown) are rarely degraded compared to Nardus pastures (grazed). Within pastures, eutrophic plants are most abundant on small pastures with low soil carbon/nitrogen ratio, indicating high nutrient availability. Nardus stricta dominance is most problematic on north‐exposed slopes and in summer pastures. A plausible driver of both degradation trends is the grazing management regime: within small pastures at low elevation where the grazing periods are short but intense, soil carbon/nitrogen ratio is low because of high dung deposition, thus the eutrophic species become dominant. Contrastingly, on large summer pastures with low‐intensity and long‐term grazing, N. stricta becomes dominant due to selective grazing. Both degradation trends show a negative impact on the orthopteran density. Conclusion: Species‐rich Nardus grasslands are a precious alpine habitat for specialised plant species and orthopterans. With an extensive mowing regime or a more controlled grazing regime that homogenises intensity in time and space, species‐rich Nardus grasslands can be conserved in Switzerland.     

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1. Understanding the role of environmental filtering and spatial processes along environmental gradients in assembling and maintaining aquatic communities in rare habitats is crucial for land management and biological conservation. We investigated the relative roles of environmental and spatial factors influencing beta (β) diversity of aquatic macroinvertebrate assemblages in 36 interdunal wetlands from five freshwater sand dune areas across two ecoregions spanning the latitudinal gradient of Lake Michigan. We hypothesised that aquatic macroinvertebrate diversity and composition would vary along the coastline because of an underlying environmental gradient. We predicted high species replacement correlated with environmental (local and regional) conditions and increasing species diversity with decreasing latitude.
2. We calculated sample completeness, obtained diversity estimates based on Hill numbers and used abundance-based β partitioning and multivariate analysis to examine β diversity, and its replacement and nestedness components in relation to local and regional predictors.
3. Despite a short latitudinal gradient, we detected a significant increase in species richness with decreasing latitude, underpinned by a strong temperature and precipitation gradient. Species replacement (balanced variation in abundance) was high at all spatial scales (wetland, dune area, ecoregion and coastline), and correlated with local and regional environmental variables.
4. Community dissimilarity showed no marked increase with spatial extent, which suggests a system where local-scale environmental filtering prevents dispersal driven homogenisation. Both local and bioclimatic factors were correlated with aquatic macroinvertebrate dissimilarity, but local factors played a larger role.
5. This study simultaneously examined the response of alpha and β diversity to geographical and environmental variables. Our results indicate that macroinvertebrates respond to abiotic factors by tracking suitable environmental conditions among locally variable interdunal wetlands. Thus, high dispersal along the coastline conveys resiliency to a hydrologically dynamic wetland system, which allows aquatic macroinvertebrates to contribute an integral portion of sand dune biodiversity within the Laurentian Great Lakes region. The high species turnover found suggests that conservation strategies should consider coastline connectivity among dune areas to maintain freshwater biodiversity.