The present study deals with the ecological impacts of the introduction of two alien species of piscivorous fish in several lakes of the Middle Rio Doce lake district in Minas Gerais, Brazil. It was ...demonstrated that these effects were not restricted only to the fish community. The introduction of the predatory red piranha Pygocentrus nattereri and the tucunaré Cichla cf. ocellaris caused not only a sharp decrease in the number of native fish species, but also major shifts in other trophic levels. Just after the fish were introduced, most lakes began to show conspicuous changes in phytoplankton species composition, in which Cyanophyceae gradually came to dominate. The zooplankton community lost several species, and in some cases, such as Lake Carioca, all the cladoceran species disappeared. On the other hand, invertebrate predators, represented by the dipteran Chaoboridae, boomed in the lake, with higher densities of exotic species, probably as a result of the 'ecological release' by reduction of the original fish fauna. There was a general trend of species loss in different trophic levels. All these changes are apparently associated with decreases in water quality. The present situation in these lakes demands new approaches to the management and conservation of these ecosystems.
The present study deals with the ecological impacts of the introduction of two alien species of piscivorous fish in several lakes of the Middle Rio Doce lake district in Minas Gerais, Brazil. It was ...demonstrated that these effects were not restricted only to the fish community. The introduction of the predatory red piranha Pygocentrus nattereri and the tucunare Cichla cf. ocellaris caused not only a sharp decrease in the number of native fish species, but also major shifts in other trophic levels. Just after the fish were introduced, most lakes began to show conspicuous changes in phytoplankton species composition, in which Cyanophyceae gradually came to dominate. The zooplankton community lost several species, and in some cases, such as Lake Carioca, all the cladoceran species disappeared. On the other hand, invertebrate predators, represented by the dipteran Chaoboridae, boomed in the lake, with higher densities of exotic species, probably as a result of the "ecological release" by reduction of the original fish fauna. There was a general trend of species loss in different trophic levels. All these changes are apparently associated with decreases in water quality. The present situation in these lakes demands new approaches to the management and conservation of these ecosystems.
The present study deals with the ecological impacts of the introduction of two alien species of piscivorous fish in several lakes of the Middle Rio Doce lake district in Minas Gerais, Brazil. It was ...demonstrated that these effects were not restricted only to the fish community. The introduction of the predatory red piranha Pygocentrus nattereri and the tucunaré Cichla cf. ocellaris caused not only a sharp decrease in the number of native fish species, but also major shifts in other trophic levels. Just after the fish were introduced, most lakes began to show conspicuous changes in phytoplankton species composition, in which Cyanophyceae gradually came to dominate. The zooplankton community lost several species, and in some cases, such as Lake Carioca, all the cladoceran species disappeared. On the other hand, invertebrate predators, represented by the dipteran Chaoboridae, boomed in the lake, with higher densities of exotic species, probably as a result of the "ecological release" by reduction of the original fish fauna. There was a general trend of species loss in different trophic levels. All these changes are apparently associated with decreases in water quality. The present situation in these lakes demands new approaches to the management and conservation of these ecosystems.O presente estudo trata dos impactos ecológicos da introdução de duas espécies invasoras de peixes piscívoros em diversos lagos da região lacustre do médio rio Doce em Minas Gerais, Brasil. Demonstrou-se que estes efeitos não se restringiram às comunidade de peixes. A introdução dos predadores Pygocentrus nattereri (piranha-vermelha) e Cichla cf. ocelaris (tucunaré) não só causou uma forte redução no número de espécies de peixes nativos, como também mudanças nos níveis tróficos inferiores. Pouco depois das introduções, a maioria dos lagos começou a mostrar alterações na comunidade fitoplanctônica, tais como o aparecimento da dominância de Cyanophyceae. A comunidade zooplanctônica perdeu diversas espécies e, em alguns casos, houve o desaparecimento de todas as espécies de cladóceros limnéticos, como é o caso da lagoa Carioca. Por outro lado, predadores invertebrados, representados pelos dípteros da família Chaoboridae, floresceram nos lagos com maiores densidades de espécies exóticas de peixes, provavelmente como resultado da "liberação ecológica" causada pela redução da ictiofauna original. Além de uma tendência geral de perda de espécies em diferentes níveis tróficos, outras mudanças estão aparentemente associadas com a redução da qualidade de água. Dessa forma, esses ecossistemas estão necessitando urgentemente de novas abordagens nas estratégias de manejo e conservação.
Soil organic carbon (SOC) retention is a function of climate, vegetation, drainage, and management interactions, but also of intrinsic soil properties such as texture, mineralogy, and structure. To ...assess these edaphic controls, three soils of the Brazilian savanna (Cerrado) under similar climate, vegetation, and slope but of contrasting texture were sampled to 1-m depth and characterized for textural, chemical, and mineralogical properties, and SOC concentration (in bulk samples and clay, silt, and sand fractions). The basic assumption was that SOC particle size determines its retention mechanism: colloidal forms are retained by sorption, while particulate organic matter (>20 μm) can occur outside or inside aggregates. It was hypothesized that SOC retention is controlled simultaneously by soil texture, mineralogy, and depth. The three soils are clayey, loamy, and sandy Haplustox, all kaolinitic with minor contents of Fe and Al oxides, vermiculite, and illite. The SOC concentrations in particle size fractions were inversely related to the content of the respective fraction in soil (SOC dilution effect), thus SOC partition is better assessed by determination of SOC pools in each particle size on a total soil mass basis rather than on a size-fraction concentration basis. The positive linear relations between SOC and clay + silt concentrations in bulk soil were explained mostly by greater clay-sized SOC pools, which could be modeled as a function of clay content (related to specific surface area) and depth. Quantitative clay mineralogy showed that bulk SOC and clay-sized SOC pools were well correlated with Fe oxides in topsoil and amorphous Al oxides in subsoil, but this mineralogical control is secondary to the textural control, since it depends on clay content.
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Land use conversion from natural to agricultural ecosystems affects concentration and storage of soil organic carbon (SOC) depending on tillage frequency and depth, soil type, climate and other ...factors. Despite its importance, little is known about the magnitude and consistency of changes in SOC stocks (Mg
ha
−1) due to management of highly weathered soils in Brazil. From 37
uncultivated/cultivated paired sites in Brazil (most on Oxisols), SOC stocks were calculated for the depths of 0–20 and 0–40
cm. Changes in SOC stocks were calculated for intensive (with annual tillage) and non-intensive (pastures, conservation tillage and perennial crops) land use systems. Intensive systems caused significant (
t-test,
P
<
0.05) SOC loss of 10.3% or 6.74
Mg
ha
−1 in the 0–20
cm depth, but not in the 0–40
cm depth. In general, non-intensive systems had no significant effect on SOC stocks in the 0–20 and 0–40
cm depths. However, in coarse-textured soils (≤200
g
clay
kg
−1), non-intensive systems caused significant SOC losses of about 20% for both 0–20 and 0–40
cm depths (8.5 and 15.5
Mg
SOC
ha
−1, respectively). No significant changes in SOC were detected in Oxisols (<500
g
clay
kg
−1) and clayey Oxisols (≥500
g
clay
kg
−1), in five arbitrary ecoregions or under the three different non-intensive land use systems. Average SOC losses under intensive and non-intensive systems were low in comparison to those reported for temperate ecosystems, probably due to: (a) lower SOC stocks in surface when compared to temperate soils, and (b) strong interaction of Al/Fe oxides in clay with SOC.
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Cutaneous secretions of toad species are an important source of bufadienolides, compounds that exhibit interesting structural features and biopharmacological properties. Here we describe the ...isolation of bufadienolides from the Brazilian toad
Rhinella schneideri parotoid glands secretion, including: marinobufagin (
1), bufalin (
2), telocinobufagin (
3), hellebrigenin (
4), and the atypical 20
S,21
R-epoxymarinobufagin (
5) besides the widespread
β-sitosterol (
6). Starting from natural bufadienolides four derivatives were prepared: 3
β-acetoxy-marinobufagin (
7), 3
β-acetoxy-bufalin (
8), 3
β-acetoxy-telocinobufagin (
9), and 3
β-acetoxy-20
S,21
R-epoxymarinobufagin (
10). The cytotoxic evaluation showed that all natural bufadienolides and their derivatives exhibited moderate to strong activity against human HL-60, SF-295, MDA-MB-435, and HCT-8 cancer cell strains without hemolysis of mouse erythrocytes. The acetylated bufadienolides (
7–9) and the epoxide
10 showed lesser peripheral blood lymphocytes (PBLs) inhibitory activity than their precursors, suggesting that chemical modifications on such compounds can play an important role on the modulation of their cytotoxic profile.
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To reduce the number of pending cases and conflicting rulings in the Brazilian Judiciary, the National Congress amended the Constitution, allowing the Brazilian Supreme Court (STF) to create binding ...precedents (BPs), i.e., a set of understandings that both Executive and lower Judiciary branches must follow. The STF's justices frequently cite the 58 existing BPs in their decisions, and it is of primary relevance that judicial experts could identify and analyze such citations. To assist in this problem, we propose LegalVis, a web-based visual analytics system designed to support the analysis of legal documents that cite or could potentially cite a BP. We model the problem of identifying potential citations (i.e., non-explicit) as a classification problem. However, a simple score is not enough to explain the results; that is why we use an interpretability machine learning method to explain the reason behind each identified citation. For a compelling visual exploration of documents and BPs, LegalVis comprises three interactive visual components: the first presents an overview of the data showing temporal patterns, the second allows filtering and grouping relevant documents by topic, and the last one shows a document's text aiming to interpret the model's output by pointing out which paragraphs are likely to mention the BP, even if not explicitly specified. We evaluated our identification model and obtained an accuracy of 96%; we also made a quantitative and qualitative analysis of the results. The usefulness and effectiveness of LegalVis were evaluated through two usage scenarios and feedback from six domain experts.
Little is known about the interdependence between soil organic carbon (SOC) and texture within the soil profile. In order to describe mathematically this relation, three highly weathered soils ...(sandy, loamy and clayey) in the Brazilian Cerrado under similar climate, vegetation and topography were sampled in triplicate to 1-m depth and analyzed for texture and total SOC concentration. The SOC concentration was directly and linearly correlated with the combined clay
+
silt (but not to clay) content for all depths. The intercept and slope of these linear relations decreased with depth following exponential and logarithmic functions (
P
<
0.001,
R
2
=
0.97 and 0.95, respectively). These mathematical functions permitted the adjustment of the intercept and slope parameters of a SOC
=
a
+
b(clay
+
silt) function for any depth in the 0-1 m interval. This profile pedotransfer function precisely estimated SOC concentration (
P
<
0.0001,
R
2
=
0.92) up to 1.0 m of the studied soils. Using data from different Cerrado soils, estimated vs. measured SOC relations with similarly high
R
2 values were obtained, despite slopes and intercepts were different than 1 and 0. This indicates that for the Cerrado region the textural control of SOC varies predictably with depth, and the proposed model can be calibrated to estimate SOC in subsurface layers of highly weathered soils.
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A large area (180
Mha) of central Brazil is occupied by a savanna biome known as the Cerrado. Annual rainfall in this region varies from 1200 to 2000
mm, although there is a long (∼5 month) dry ...season with almost no rain. This region is regarded by Brazilians as their agricultural frontier and there is a steady growth in the area dedicated to permanent cropping in the region, which today is estimated to occupy 14
Mha. Owing to the dearth of long-term experiments, the impact of continuous cropping on soil carbon stocks remains unclear. The objective of this study was to evaluate the effects of different tillage systems (zero till (ZT) and conventional tillage (CT)) on the change in soil carbon stocks over a 20-year period of the same crop sequence compared to that under a neighbouring area of native vegetation (NV). Only approximately 10
Mg
ha
−1 of soil carbon in the 0–100
cm depth interval was lost under continuous ZT. However, under CT systems losses were greater (up to 30
Mg
C
ha
−1) when the mouldboard plough was used and/or tillage was performed twice a year. We did not have access to instrumentation to accurately assess soil charcoal but the C/N data and peroxide and dichromate oxidative techniques suggested that ∼40% of soil C was in this form. The
13C natural abundance of soil profiles indicated that residues of crops (maize) and the spontaneous annual fallow of
Brachiaria spp. resulted in integration of significant C
4 residues to a depth of at least 40
cm. It would appear that zero tillage, which is already widely adopted in the Cerrado region of Brazil, will have only a small negative long-term impact on soil C stocks, but ploughing, especially more than once a year, will lead to considerably larger soil C losses.
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The increase in the emergence of antibiotic-resistant microorganisms and difficult to treat infections caused by these pathogens stimulate research aiming the identification of novel antimicrobials. ...Skin secretion of amphibian contains a large number of biologically active compounds, including compounds that performance defense mechanisms against microorganisms. In the present work, two antimicrobial bufadienolides, telocinobufagin (402.1609
Da) and marinobufagin (400.1515
Da), were isolated from skin secretions of the Brazilian toad
Bufo rubescens. The specimens were collected in Brasilia (Distrito Federal, Brazil), the skin secretions extracted by electric stimulation, and submitted to purification by RP-HPLC. The molecular structure and mass determination were done by
1H and
13C NMR and mass spectrometry data, respectively. The antimicrobial activity was performed by liquid growth inhibition against
Staphylococcus aureus and
Escherichia coli. The minimum inhibitory concentrations of telocinobufagin and marinobufagin were, respectively, 64.0 and 16.0
μg/mL for
E. coli and both 128
μg/mL for
S. aureus. Besides the antimicrobial activity both bufadienolides promoted an increase of the contraction force in isolated frog ventricle strips.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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