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Recent changes in the distribution and rooting elevation of Schoenoplectus club‑rushes in the Scheldt estuary and the consequences for their survival
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Abstract We aimed to assess the distribution and trends in abundance and rooting elevation in relation to substrate type (soft sediment/riprap) for three Sch‑ oenoplectus club-rush species in the Zeeschelde estuary (Belgium). Surveys took place in 1995, 2003 and 2013, following dike fortifcations for the SIGMA food control plan. Compared to 1995 club-rush tufts are now positioned lower in the tidal frame, especially their upper margin. Club-rush cover decreased by 50% in the last time interval. This is linked to marsh succession after a vegetation set-back by SIGMA works and increasing competition with Phragmites and Salix. The lower margin of club-rushes shifted downwards on riprap, but not on soft sediment. This substrate-dependent rooting elevation reach likely indicates that substrate stability can be an important factor for club-rush persistence and growth on the lower marsh margin. This emerged only recently probably because tufts needed time to expand after the SIGMA works and because of the improved water quality. Currently, Schoenoplectus club-rushes on soft sediment in the Zeeschelde sufer from the lack of suitable areas with cyclic natural morphodynamics that maintain pioneer habitat. To maintain club-rush diversity we suggest to manage threatened club-rush populations or to translocate them to newly created restoration sites.
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Ant nests effect on organic matter, carbon, and nitrogen flux in the soil under grasses tufts in Lamto savannah (Côte d’Ivoire)
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Ants are known to contribute to the physical and chemical improvement of the soil. In this context, the hypothesis put forward is that ants improve the nitrogen (N) supplementation necessary to ensure the high primary production measured in the Lamto savannah. Recent investigations in the humid savannah ecosystem showed that ant nests’ association with perennial grasses enhances their growth, productivity, and microorganism activity. This study aimed at understanding the effect of ant nests on organic matter (OM), carbon (C), and N flux beneath grass tufts. Under each grass tuft chosen to carry out this study, soil samples were taken from the depths of 0–10 cm using an auger at shrubby, clear grassy, and transitional grassy savannah. The analytical method by incineration of the loss on fire was used to determine the OM amount. The Kjeldahl method was used to determine the total N amount in the soil under grass tufts. The results showed that these components’ amount is higher beneath grass tufts associated with ant nests than those not associated with ant nests. The presence of ant nests increases OM and C amount in the soil under Hyparrhenia diplandra tufts than Andropogon schirensis, and Loudetia simplex tufts. In contrast, N amount is higher under L. simplex tufts than A. schirensis; but mean under H. diplandra. The carbon/nitrogen ratios less than 10 indicate high OM mineralization under grass tufts associated with ant nests. This provides the plants with an adequate supply of nutrients
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They live under our streets: ant nests (Hymenoptera, Formicidae) in urban pavements
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In the context of global insect decline, the urbanisation process plays a key role. However, urban pavements, which are considered to be impervious to biodiversity, can harbour ground-nesting insects under certain conditions. Recent observations have revealed the presence of Formicidae nests under urban pavements. The aim of this work is to determine the species richness of Formicidae nesting under urban pavements in the Brussels-Capital Region (Belgium) and to characterise their nest environment and soil texture. Seven ant species were identified in 120 nesting sites: Lasius niger, Lasius brunneus, Lasius flavus, Lasius fuliginosus, Tetramorium caespitum, Tetramorium impurum and Myrmica rugulosa. Concrete slabs or natural stones with a sandy sub-layer are the main structures in which ants nest. In addition, nests were mainly found under modular pavements with degraded rigid joints. The results of this work highlight the capacity of urban structures to host part of ant biodiversity in cities.
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Impact of chemical fertilizers on diversity and abundance of soil-litter arthropod communities in coffee and banana plantations in southern Rwanda
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Few studies explored effects of chemical fertilizers on diversity and abundance of soillitter arthropods in the tropics. To fill this gap, a study focussed on the abundance of soil-litter arthropods and selected soil physicochemical properties in coffee plantations treated with chemical fertilizers and in plantations of coffee and banana treated with organic fertilizers and organic mulches in southern Rwanda. Each land use was replicated three times. Soil-litter arthropods were collected using pitfall traps and hand collection. They were identified to the family level using dichotomous keys. Soil have been collected using auger and taken to the laboratory for the analysis of soil pH, soil organic carbon, total nitrogen, phosphorus, and cation exchange capacity. Findings indicated a total of 12,945 individuals distributed into 3 classes, 16 orders, 50 families and 92 morphospecies, with higher abundance and diversity in coffee plantations treated with organic fertilizers and organic mulches. Collected soil-litter arthropods were mainly classified in the class Insecta, dominated in numbers by ants (Hymenoptera: Formicidae), while Coleoptera and Hemiptera had more families. However, soil under coffee plantations treated with organic fertilizers and organic mulches was acidic compared with the soil under coffee plantations treated with inorganic fertilizers and banana plantations treated with organic fertilizers and organic mulches. The relationships between soil-litter arthropods and soil physicochemical properties suggest that soillitter arthropods respond to the land use independently from soil physicochemical properties. We recommend further studies in coffee and other crop plantations in other regions of Rwanda to verify the findings of this study.
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Preface: Emerging trends in aquatic ecology IV
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Our understanding of aquatic ecology and ecosystem functioning continuously improves. The special issues of Hydrobiologia on “Emerging Trends in Aquatic Ecology” each represent a collection of papers to testify to the variety of approaches and topics that concur in reaching the common aim to scientifcally underpin political and societal decisions to mitigate our impacts on our planet and its biodiversity.
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Six new species of Elpidium Müller, 1880 (Podocopida: Limnocytheridae) from Eastern Brazil
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Elpidium is the most common ostracod genus occurring in phytotelmata in the Neotropical region, with distributions ranging from Florida, USA in the north to Rio Grande do Sul, Brazil in the south. However, the genus remains poorly known both in terms of diversity and of the distributional pattern of its species. Here, we describe six new species of Elpidium, E. oxumaen. sp., E. cordiforme n. sp., E. picinguabaensen. sp., E. eriocaularumn. sp., E. higutiaen. sp., E. puriumn. sp., all from phytotelm environments in the Brazilian Atlantic rain forest. In addition, we discuss the distributional pattern and endemicity levels of Elpidium species in the light of these new taxonomic results and argue about possible misunderstandings on the distribution of the type species E. bromeliarum.
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Evidence for Conductivity- and Macroinvertebrate-Driven Segregation of Ostracod Assemblages in Endorheic Depression Wetlands in North West Province of South Africa
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Our knowledge of the ecology of non-marine Ostracoda inhabiting endorheic wetlands (pans) of the semi-arid regions of South Africa is very scarce. The present study investigates the distribution of ostracod species in grass, open, and salt pans in the central part of the North West province and tests ostracod response to abiotic and biotic predictor variables operating at a local scale. Distance-based linear models revealed three variables (pan type, water electrical conductivity and abundance of macroinvertebrate predators, and collector-gatherers) that best explained variation in the ostracod dataset. Ostracod assemblages from the three studied pan types differed by the dominance structure rather than by the species composition. Salt pans with high conductivity and high ratio of predaceous macroinvertebrates were dominated by Heterocypris giesbrechti, with accessory presence of Plesiocypridopsis newtoni. In open pans with low conductivities and the lowest ratio of predators (but highest ratio of collector-gatherers) Potamocypris mastigophora was typically a dominant species, while in grass pans, all the three mentioned species had similar relative abundances. Although our findings lend provisional support to some models of ostracod assemblage diversity across different pan types, more studies replicating endorheic depression wetlands in other regions are required before generalizations can be made.
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On Caledromus robinsmithi, a new genus and species of Psychrodromini Martens, 2001 (Crustacea, Ostracoda, Herpetocypridinae) from New Caledonia (Pacific Ocean)
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The New Caledonian Archipelago is a hot spot for biodiversity and endemism. Whereas popular groups such as birds and plants are well-studied, invertebrate groups such as ostracods remain ill-known. Here, Caledromus robinsmithi gen. et sp. nov. is described from a single locality on ‘Grande Terre’, the main island of the archipelago. The new genus belongs to the Psychrodromini, one of the four tribes in the subfamily Herpetocypridinae (family Cyprididae). Caledromus gen. nov. can be distinguished from all other herpetocypridinids by a combination of the following factors: the absence of marginal septa in both valves, the mildly developed marginal valve structures, the small Rome organ on the A1, the total reduction of the five natatory setae on the A2, the rectangular second palp segment of the Mx1, the broad and asymmetrical palp on the female T1, the absence of additional postlabyrinthal coils in the Hp and the seta Sp of the CR which is a fixed spine. Because of the close similarity to the genus Psychrodromus, the new genus is thought to have Palaearctic affinities, contrary to other ostracod species in New Caledonia, which are either circumtropical or with Australian zoogeographical connections.
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Natural populations of the putative ancient asexual Darwinula stevensoni (Crustacea, Ostracoda) differ in their microbiomes
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Although ostracods are important components in aquatic ecosystems, little is known about their microbiomes. Here, we analyzed the microbiomes of the putative ancient asexual ostracod species, Darwinula stevensoni, in three natural populations from different freshwater habitats in the UK, Belgium, and Spain. We applied high-throughput amplicon sequencing approaches to analyze the V3–V4 part of the bacterial 16S rRNA region. We tested for host-specific microbiomes by comparing bacterial assemblages of ostracods with those of sediment and water samples from the same locations. Around 2,200 Amplicon Sequence Variants (ASVs) were identified from ostracod samples with universal primers and 1,700 ASVs with endosymbiotic-specific primers, illustrating a high microbiome diversity in D. stevensoni. Most bacterial taxa were unique to the microbiome of D. stevensoni as compared to other freshwater invertebrates and to non-marine ostracods. Alpha diversity of ostracod microbiomes did not differ significantly between the three populations, but PERMANOVA detected significant differences in bacterial compositions. Microbiomes varied highly among ostracod specimens from the same population. Possible factors shaping ostracod microbiomes could be latitude, food, age, and environmental variables. Preliminary functionality analyses showed that Darwinula-specific microbiomes contribute to lipid, carbohydrate, nucleotide, and amino acid metabolic processes and the synthesis of co-factors and vitamins.
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Environmental correlates of non-marine ostracod (Crustacea: Ostracoda) assemblages of the Eastern Cape (South Africa)
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The present study investigates the ecology and distribution of ostracod species and assemblages from 62 inland waterbodies in the Eastern Cape province of South Africa and tests the influence of two major climatic zones (Arid steppe climate BS and Warm temperate humid climate Cf) and two primary catchments (Kowie and Great Fish Rivers), as well as broad gradients of altitude and several local environmental factors. Distance-based linear models were used to test these species-environment relationships and indicated that eight variables (water temperature, pH, conductivity, waterbody size, habitat type, altitude, hydrological-drainage, climate) individually showed significant correlations with the response ostracod dataset of 35 species. However, owing to substantial collinearity, the most parsimonious model identified only two predicting variables (climatic zone and water pH) which best explained variation in ostracod assemblage composition. The assemblages of the two climatic zones differed significantly, with Plesiocypridopsis newtoni and Sarscypridopsis ochracea being most commonly found in the BS climates, while Sarscypridopsis trigonella and Physocypria capensis occurred most frequently in the Cf climates. Finally, tolerance ranges to water pH and electrical conductivity for 21 ostracod species are provided to facilitate application of ostracods in further biodiversity and water-quality assessments, as well as in palaeo-environmental reconstructions.
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