Eastern Amazon Research Articles

Iron Islands: The importance of iron caves in the eastern Amazon for bat conservation

AbstractThe Carajás region is home to the largest number of iron caves in Brazil, but studies that integrate elements of biological diversity and landscape characteristics are scarce. We present the first study based on the bat cave vulnerability index (BCVI), which uses bats as a key species for prioritizing caves in South America, whose objective was to assess the biotic potential and vulnerability of caves in the Carajás region, determining priority sites and the most effective conservation actions. The study took place from August 2021 to March 2023, where an inventory of the chiropterofauna of 12 caves was carried out. We recorded 16 bat species, two of which are vulnerable to extinction – Furipterus horrens (Cuvier, 1828) and Natalus macrourus (Gervais, 1856) – and two endemics to the Amazon region – Hsunycteris aff. thomasi (Allen, 1904) and Phyllostomus latifolius (Thomas, 1901); as well as one species with insufficient data to delimit its endemicity or threat status (Lonchophyllinae sp.). Mining is the main anthropogenic activity in the region, but tourism is also present and acts as a potential source of disturbance to the caves. The BCVI revealed three high priority caves for conservation and four with medium priority, indicating that these habitats are vulnerable to species loss and population decline due to exposure to anthropogenic activities and habitat destruction, thus requiring more effective conservation strategies. Considering the uniqueness of the subterranean habitats, we recommend re‐evaluating the proposals for expanding mining activities, implementing controlled tourist visitation plans and conducting ecological studies and long‐term monitoring.

Flows in urban water bodies in the eastern Amazon: concepts, measurements and water quality

There are numerous problems with measuring flows in streams in the Legal Amazon, including urban growth and the high cost of instruments for this variable. The aim of this research was to identify the main concepts and types of flow in the literature, the ways in which they can be measured, as well as ways of intervening in the water quality of this water variable, for application in the Paragominas stream, urban stretch. The method applied was exploratory, quantitative and qualitative, and observational in nature. The data obtained indicated that the concepts identified in the 29 pieces of literature selected are similar. The 11 types of definitions involve the uses of water (n = 15; 28.6%); there were four types of measurement instruments, with the use of floats standing out (n = 5.0; 38.5%). Comparative studies on the quality of measurements made with hydraulic windlasses and floats (n = 1.0; 7.7%) showed values with low differences in streams (0.1m3/s ≤ Q ≥ 0.4 m³/s). Based on these data and the physical irregularities reported by the selected authors, it is concluded that the latter method is effective for measuring the water body under study in the urban area of the municipality of Paragominas, Pará, Brazil. The data contained here can be used to assist in water management in this municipality, as well as flood control and prevention.

Spatio-temporal analysis of the red ring pathosystem in Oil palm in the Eastern Amazon

The objective was to evaluate the spatial and temporal distribution of the Red Ring and R. Palmarum in conventional oil palm plantation in the municipality of Thailand, state of Pará, in the production area of the AGROPAR Farm, belonging to the AGROPALMA SA Company, through of data obtained monthly from a Historical series from 2014 to 2018, using Geostatistics as a tool. To evaluate the dispersion of the Red Ring and R. Palmarum, sequential sampling was used. In this way, semivariograms were generated and the theoretical models were tested: Spherical, Gaussian, exponential and linear (pure nugget effect). The obtained semivariograms were submitted to the Krigagem estimator to make the dispersion maps of the Patosystem. Through the semivariograms it was observed that the model that best fit the spatial distribution of the red ring was the Gaussian, with range values for the experimental area ranging from 690 m to 870 m. As for the distribution of R. Palmarum, the models that best fit were the spherical and exponential, with values ranging from 860 m to 4990 m and that the R. palmarum infestation is preferably located on the periphery of the courts.

Thermal Comfort of Nelore Cattle (Bos indicus) Managed in Silvopastoral and Traditional Systems Associated with Rumination in a Humid Tropical Environment in the Eastern Amazon, Brazil.

The objective of this study was to evaluate the thermal comfort of Nelore cattle (Bos indicus) managed in silvopastoral and traditional systems associated with rumination behavior in a humid tropical environment in the Eastern Amazon, Brazil. The study was carried out on a rural property in Mojuí dos Campos, Pará, Brazil, during the transition period of the year, from June to July 2023. Over these two months, six consecutive data collection days were held. We selected 20 clinically healthy non-castrated male Nelore cattle, aged between 18 and 20 months, with an average weight of 250 kg and body condition score of 3.5 (1-5). These animals were randomly divided into two groups: traditional system (TS) and silvopastoral system (SS). The physiological variables evaluated included RR, RT and BST. The variables were analyzed using the linear mixed model. For agrometeorological variables, higher values were observed between 10:00 a.m. (33 °C) and 6:00 p.m. (30 °C), with the highest temperature observed at 4:00 p.m. (40 °C). The RR showed interactions (p = 0.0214) between systems and times; in general, higher RR were obtained in the Traditional. The animals' RT showed no significant difference (p < 0.05) between the production systems, but there was a statistically significant difference in relation to the time of collection (p < 0.0001). In the BGHI, it was possible to observe that there was mild stress in the period from 22:00 at night to 6:00 in the morning and moderate stress in the period of greatest increase in temperature, from 10:00 in the morning to 18:00 at night. BST showed no statistical difference between the regions studied or between the SP (35.6 °C) and TS (36.25 °C) systems. RT in the TS showed a positive correlation with AT (r = 0.31507; p = 0.0477). RT in the SP showed a positive correlation with THI (r = 35583; p = 0.0242). On the other hand, RT in the SP (r = 0.42873; p = 0.0058) and ST (r = 0.51015; p = 0.0008) showed a positive correlation with BGHI. RR in the TS showed a positive correlation with BGHI (r = 0.44908; p = 0.0037). The greatest amounts of rumination were carried out by animals in the SP system, generally ruminating lying down (p < 0.05). With regard to rumination behavior in the morning and afternoon, there were higher numbers of WS and LD in the TS (p > 0.05). Most of the time, the cattle were LD during the morning and afternoon shifts, and at night and dawn they were WS in the TS. Therefore, the SP offers more thermal comfort advantages compared to the TS system.

Mites associated with açaí palm trees (Euterpe oleracea: Arecaceae) in native and cultivated areas of the state of Pará (Eastern Amazon, Brazil).

The objective was to quantify and analyze the diversity of mites associated with native and cultivated açaí palms crops, as well as their distribution in the dry and rainy seasons in the municipalities of Bragança and Augusto Corrêa, state of Pará. Rarefaction curves were generated for diversity values using the statistical programming language R, rarefaction curves for estimates of richness and equitability, and analysis of variance with permutations. A total of 2069 mites from 28 families were sampled, being most representative Phytoseiidae (32.4%), Phytoptidae (13%), Cunaxidae (7.7%), Tetranychidae (5.6%) and Tydeidae (4.9%). Among predators, the most abundant species were Amblyseius sp. 1, Armascirus amazoniensis Wurlitzer & Silva, Iphiseiodes zuluagai Denmark & Muma, Scutopalus tomentosus Rocha, Skvarla & Ferla, and the phytophagous mites Acaphyllisa sp., Davisella sp., Oligonychus sp. and Retracus johnstoni Keifer. In the rainy season, more mites were sampled (n = 1176) than in the dry season (n = 893). The greatest richness was observed in the dry period (73 species) and diversity was also greater in this period. In the municipality of Bragança there was greater richness (78 species) and the cultivated açaí trees had greater acarine abundance (74.7%) than the native ones. However, natives had slightly higher wealth (6%) than those cultivated. The diversity and richness of predatory mites show the potential of the Amazon biome to be used in applied biological control.

Impact of Production Systems on the Levels of Vitamin E, β-Carotene, and Cholesterol in the Liver of Cattle Raised in the Eastern Amazon.

The nutritional composition of bovine liver, particularly in terms of vitamins E, β-carotene, and cholesterol concentration, is significantly influenced by the cattle-rearing system and diet. This study aimed to elucidate the impact of four predominant cattle-rearing systems in the Eastern Amazon region on the vitamin E, β-carotene content, and cholesterol levels in bovine liver during the rainy season. Liver-tissue samples were collected from 48 cattle, with twelve specimens representing each rearing system. The systems encompassed two native pastures located in flood-prone areas, cultivated pastures on upland terrain and a confinement-rearing system. Our findings indicate that, when considering all rearing systems collectively, there were no significant differences in the levels of vitamins and cholesterol in the liver tissues (p > 0.05). However, a marked disparity in cholesterol levels emerged when comparing intensive rearing systems to extensive ones, with the former demonstrating notably higher concentrations (p = 0.01). Additionally, the intensive rearing system was associated with elevated levels of β-carotene (p < 0.01), α-tocopherol (p = 0.01), and β-tocopherol (p = 0.01) relative to the extensive systems. No significant variations were observed amongst the different extensive systems (p > 0.05). These results suggest that, while all rearing systems yielded liver tissues with typical concentrations of vitamins and cholesterol, the intensive rearing system led to a higher accumulation of certain vitamin compounds. This study highlights the substantial nutritional implications of different cattle-rearing systems in the Eastern Amazon and provides valuable insights for developing dietary strategies to optimize the nutritional quality of bovine liver. Therefore, the generated results are groundbreaking in the Eastern Amazon, Brazil, and inspire the development of new research projects to address other demands in this field and achieve additional outcomes.

The Effects of Urbanization and Economic Growth on The Igarapes of the Legal Amazon

This study shows the primary mechanisms causing alteration and degradation of water bodies. Data analysis on the condition of urban streams in the Eastern Amazon (53,8%) shows that Pará state is the most affected (n = 67,8%). The Almas and Mata Fome creeks in the Bengui neighborhood have undergone the most significant and irreversible environmental changes. Similarly, the Paragominas stream is experiencing ongoing harm due to urban and economic expansion. In the Western Amazon (46,1%) and Amazonas state (9.5±4.9), research on 16 streams says a housing shortage and an increase in peripheral development along these water bodies. Urbanization and economic growth are altering the ecosystem functions of urban streams, highlighting the urgent need for water management authorities in the legal Amazon region to focus on this issue.

Impact of rearing systems in the Eastern Amazon on cholesterol, β-carotene and vitamin E homologues in steer.

The quality of meat, with a focus on compounds important for human health, is directly related to the rearing systems in which the animals are produced. The search for a balanced diet, with an emphasis on low cholesterol and adequate levels of vitamins, aligns with society's emphasis on healthy eating, directly correlated with the importance of the offer made by producers for the cattle's diet. The objective was to verify the impact of different rearing systems, in the Eastern Amazon, during the rainy season, on the concentrations of vitamins (A, E) and cholesterol in the muscle (Longissimus lumborum) of crossbred Nelore cattle, castrated, aged between 24 and 36 months, and weighing between 410 and 628 kg. Twelve animals, from each of the three pasture rearing systems: native pasture in flooded areas of Monte Alegre; native pasture in a flooded area of Santa Cruz do Arari; and pasture cultivated on dry land in São Miguel do Guamá, all located in Pará, Brazil-were sampled in commercial slaughterhouses. A notable influence was observed in the concentrations of β-carotene (p < 0.01), α-Tocopherol (p = 0.02), β-Tocopherol (p < 0.01) and the combined sum of β-Tocotrienol and γ-Tocopherol (p < 0.01), as well as δ-Tocopherol (p < 0.01) when contrasting extensive with intensive systems (confinement). However, there was a difference in the content of vitamins and cholesterol between the isolated extensive systems, or between the four rearing systems (p > 0.05). Extensive systems, mainly in Monte Alegre, demonstrated greater amounts of α-Tocopherol and δ-Tocopherol. On the other hand, the intensive system exhibited higher levels of other investigated compounds, clarifying the nutritional variations generated by different livestock rearing practices in the region. Therefore, the results obtained are innovative in the Eastern Amazon, Brazil, in addition to inspiring the development of new research to meet other demands in this field, and achieve additional results, such as determining which meat, coming from cattle in production systems in the country, presents the better compositional quality of vitamins and lipids.

Soil health indicators in oil palm agroforestry systems in the eastern Amazon, Brazil

Agroforestry systems (AFSs) are generally recognized for improving soil health and increasing soil carbon (C) stock. In the Amazon region, oil palm AFSs have been promoted as a productive strategy and may offer an additional benefit of recovering degraded areas. Our objective was to evaluate whether the management practices adopted in oil palm AFSs affect soil health indicators and C stock. We carried out a study in Tomé-Açu, state of Pará, eastern Amazon, through which we evaluated two oil palm AFSs that differed in species diversity: higher diversity (AFShigh) and lower diversity (AFSlow). We used a regenerating forest (FOR) to compare with the oil palm AFSs, as regenerating forests are also a model of environmental recovery in the eastern Amazon. In the 0–10, 10–20 and 20–30 cm soil layers, we evaluated chemical indicators (active acidity (pH), calcium (Ca), magnesium (Mg), potassium (K), phosphorus (P), and aluminum (Al)), (b) physical indicators (density (SD) and stability of aggregates (AGGRE)), and (c) biological indicators (permanganate oxidizable carbon (POXC), particulate organic carbon (POC), total soil carbon (SOC content) and root stock (ROOT)). We also evaluated the total soil carbon stock (SOC stock). The values of the biological indicators in the most superficial layer, especially the C indicators, were higher in the AFSlow (C content: 1.63 ± 0.13%, POXC: 568 ± 17 mg kg−1, POC: 0.63 ± 0.10 g kg−1) and the AFShigh (C content: 1.84 ± 0.04%, POXC: 656 ± 24 mg kg−1, POC: 0.83 ± 0.06 g kg−1) than in FOR (C content: 1.35 ± 0.09%, POXC: 336 ± 10 mg kg−1, POC: 0.44 ± 0.03 g kg−1). In general, the values of chemical indicators were higher in the AFSs than in FOR, except for the Al content, which was higher in FOR than in the AFSs. The physical indicators did not show a specific pattern of variation between the AFSs and FOR; aggregate stability was higher in FOR (range throughout the soil profile: 5.57 ± 0.09 to 5.38 ± 0.24 mm) than in the AFSlow (5.41 ± 0.03 to 3.79 ± 0.07 mm) and the AFShigh (5.07 ± 0.01 to 3.79 ± 0.11 mm) in all the soil layers, and soil density was higher in the AFShigh and FOR than in the AFSlow in most subsurface layers. Therefore, oil palm AFSs improve the chemical and biological health of the soil, especially in the more superficial layers, but it does not improve the physical health of the soil when compared to the forest.

Advances in the individual authentication of cocoa beans: Vis/NIR spectroscopy as a tool to distinguish fermented from unfermented beans and classify genotypes in the eastern Amazonia

Reliable analytical methods to authenticate high-quality and economically valuable cocoa beans are highly desirable, and NIR spectroscopy stands out as a rapid and non-destructive alternative. This study employs NIR for the authentication and differentiation of 19 whole Forastero cocoa beans from Eastern Amazonia (Pará, Brazil), based on their fermentation status and genetic profiles. Partial Least Squares Discriminant Analysis (PLS-DA) models in wavelength ranges of 400–700 nm, 1400–1600 nm, and 1900–2500 nm, demonstrated high sensitivity and specificity in discriminating fermented from unfermented beans, regardless of genotype. Various compounds, including proteins, lipids, carbohydrates, anthocyanins, and theobromine, provide crucial insights into the spectral regions essential for distinction. The variable importance in projection (VIP) score value greater than 1 was used to select relevant variables, and Linear Discriminant Analysis (LDA) was performed in both the visible (472 nm and 636 nm) and infrared ranges (2096 nm and 2278 nm), demonstrating that absorbances at two specific wavelengths are sufficient for discrimination. The t-distributed stochastic neighbor embedding (t-SNE) indicated a segregation trend of the genotypes based on classification by major genetic groups in unfermented beans, suggesting that the biochemical characteristics shared by them are more prominent before fermentation. The PLS-DA models based on complete vis/NIR spectra showed comparable results in discriminating the 19 cocoa genotypes in both fermented (0.14% prediction error) and unfermented beans (0.16% prediction error). The model's classification errors can be attributed to shared genetic ancestry among the samples, primarily in unfermented beans. This research corroborates the effectiveness of vis/NIR spectroscopy as a straightforward tool for whole cocoa bean authentication, providing rapid insights into genetic diversity regardless of their fermentation state.

Integrative Taxonomy of Urocleidoides spp. (Monogenoidea, Dactylogyridae) Parasites of Pseudanos trimaculatus (Characiformes: Anostomidae) from Eastern Amazon, Brazil.

Two new species of Urocleidoides are described from the gills of Pseudanos trimaculatus (Characiformes: Anostomidae) from the coastal drainages of the Eastern Amazon, Brazil. Urocleidoides itabocaensis n. sp. is characterized by having a sclerotized, tubular, sigmoid male copulatory organ (MCO), a circular sclerotized tandem brim associated with the base of the MCO; an accessory piece articulated with the MCO, aV-shaped, divided into two subunits, distal subunit spoon-shaped; and a vaginal pore dextroventral with opening marginal. Urocleidoides omphalocleithrum n. sp. is characterized by presenting a C-shaped or sigmoid MCO; anaccessory piece articulated with the MCO, L-shaped, divided into two subunits, distal subunit gutter-shaped; a vaginal pore dextroventral with opening marginal; and aventral bar broadly V-shaped, with anteromedial projection. Molecular phylogenetic analysis based on partial 28S rDNA and COI mtDNA genes indicate that U. itabocaensis n. sp. and U. omphalocleithrum n. sp. are closely related and appear as a sister group to other Urocleidoides species (U. paradoxus, U. digitabulum and U. sinus) parasitizing anostomid fishes. This study represents the first record of monogenoids from the gills of P. trimaculatus for the Eastern Amazon.

The Gould’s Toucanet Selenidera gouldii (Natterer, 1837) (Aves: Ramphastidae) as a monotypic species

The Gould’s Toucanet Selenidera gouldii (Natterer, 1837) occurs mainly in eastern Amazonia, with a geographically isolated population in the northeast Brazilian state of Ceará. Based on two male specimens from the latter population that appeared to have a smaller body and bill with a relatively large black patch, Pinto &amp; Camargo (1961) described the subspecies S. g. baturitensis. This taxon has long been known in museum collections only by the two male specimens mentioned in its description, but recently obtained specimens have now permitted a test of its validity with larger sample sizes. Here, I examined the largest sample of S. g. baturitensis studied to date to show that S. g. gouldii and S. g. baturitensis are just the east and west ends of a broad geographic pattern of smoothly clinal differences in morphometrics that were categorized as subspecies taxa.

Stable isotopic composition of Bothrops atrox (common lancehead) in four distinct land covers in eastern Amazonia

AbstractSince consumers reflect the isotopic composition of an assimilated diet, stable isotopes can be a useful tool to address the feeding ecology of tropical snakes. This is the first study reporting carbon and nitrogen stable isotopic composition of Bothrops atrox (Linnaeus, 1758) living in different landscapes located in the lower Amazon river, encompassing four main natural landscapes of the Amazon: old‐growth forests, várzeas (flooded forests), savannas, and pastures. Our null hypothesis is that the δ13C of forest specimens of B.atrox is more negative because forests are dominated by C3 plants, while C4 plants are common in the other landscapes. On the other hand, δ15N of forest specimens should be more positive, since the δ15N of old‐growth forests are higher than plants of savanna, várzea, and pastures. Confirming our hypothesis, the δ13C of B. atrox scales of the Tapajós National Forest was approximate −25‰ to −24‰, increased to approximately −23.5‰ to −23.0‰ in the savanna and pasture, and to −21‰ in the várzea, showing an increased contribution of C4‐derived carbon. Some specimens of B. atrox had δ15N as high as 18‰, which is much higher than the average δ15N of the snake's prey (7‰), confirming the apex position of B. atrox in the Amazon region. The δ15N values of the forest specimens were 5‰ higher than the savanna specimens, and this difference decreased to 3‰ between the forest and the pasture, and the várzea specimens. Finally, there were not large differences between δ15N values of livers and scales in any of the landscapes, suggesting a constant diet through time, and reinforcing the possibility of the use of snake's scale as a less invasive and non‐lethal tissue to analyze.Abstract in Portuguese is available with online material.

For Every Love, A Pain: Impacts of Anthropic Use of Amazon Resources and Preservation Proposal

Objective: This work aims to identify how anthropogenic actions have been limiting the natural resources of the region and how the reduction of the availability of these same resources also limit anthropic actions. Theoretical Reference: Topics such as the Amazon biome, climate change and the anthropic use of natural resources were addressed. To understand the social universe of the Amazon, he also delved into traditional communities and peoples and their agrarian trajectories for the use and preservation of the environment. Method: It is a research of a social and applied nature, of a qualitative approach, with exploratory and explanatory objectives, with case study delineation as a technique of investigation, with bibliographic analyzes. Results and discussion: This research identified the anthropic actions that most affected the Brazilian Eastern Amazon and brought as a proposal alternatives of environmental planning in a sustainable way that can reduce the consequences of these activities to sustainable limits and thus bring a balance between the activities of nature and the activities of man. Research Implications: It contributes to the development of future research on the social and environmental impacts that each of the anthropic activities generates (or can still generate) in the Brazilian Eastern Amazon. Originality/value: This is an unprecedented piece of research for the Brazilian Eastern Amazon that, at the moment, is about severe environmental alterations as a result of the anthropic use of its natural resources and brings light, proposals for the preservation of the region's sociobiodiversity.

Schistosoma mansoni infection in residents of a riverside community in Eastern Amazon.

Schistosoma mansoni worms cause a waterborne parasitic disease called schistosomiasis. It commonly affects individuals in lack of sanitation structure. In Brazil, Pará state has Belém as one of the worst sanitation-ranking places in 2023, where schistosomiasis transmission was already documented. This study reports the occurrence of schistosomiasis in residents of Ilha das Onças, an island next to Belém. Stool samples were obtained from participants over 2 years old, all residents from Furo do Rio Grande, one of the rivers on the island. The Kato-Katz technique was performed for parasite investigation in the stool samples. Each participant responded to a sociodemographic and clinical questionnaire. The residences were georeferenced for map designing. Three out of 263 participants were S. mansoni positive, all men, ages ranging from 19 to 41 years old, with low parasitic load. Malacological surveys were carried out, but no Biomphalaria snails were found. Risk factors for schistosomiasis establishment are present on the island, and the lack of sanitation makes it a potential risk area. Malacological surveys are highly encouraged as preventive measures, as well as health surveillance for riverside populations, generating data that will help health authorities in the management and planning of preventive control actions.

Signature of logging in the Brazilian Amazon still detected after 17 years

Selective logging in the Amazon Biome holds significant importance economically and environmentally. Due to its potential for forest degradation, monitoring these areas is of utmost importance. We assessed canopy openness in sustainably logged forest areas in Eastern Amazonia using hemispherical photos taken in areas that were logged in different years (2004, 2007, 2017, 2019, and 2021), along with one unlogged control area to evaluate the time period over which the effects of logging remained detectable. Timeframes of detectability varied across logging features considered (e.g. log landings, logging roads and skid trails). Canopy openness of log landings used to store logs was still greater than that of unlogged forests controls >17 years after logging had ceased while the impacts of logging roads and skid trails were still detectable at least 5 years after cessation of logging. The detection of the impacts of selective tree harvesting on the forest several years after the end of operations provides confidence for larger-scale quantification of historical low-intensity logging over Amazonia through high-resolution imagery. More generally, the study also highlighted the importance of monitoring selective tree extraction areas to understand their influence on forest disturbance and the occurrence of regeneration processes.

Life history of an evolutionary distinct aquatic caecilian amphibian (genus Potomotyphlus) in eastern Amazonia, Brazil

Abstract Basic ecological data for caecilians are relatively lacking. This study presents the first comprehensive ecological investigation of the Amazonian aquatic caecilian Potomotyphlus kaupii, utilizing a large sample size. We collected population data over a 14-month period, and also used data of museum specimens, both from Belém, State of Pará, Brazil. Our analysis focused on sex ratio, sexual size dimorphism (SSD), female fecundity, and ecological observations. No significant differences in adult sex ratio were found. SSD was found in some characters such as circumference at midbody and body mass with females being larger than males, while males had a wider and longer cloacal disc. We provide the first determination of the approximate size at which males diverge from females in the terminal portion of the body, demonstrating an allometric growth pattern of the cloacal region. Female size showed a positive correlation with the number of ovarian eggs, indicating an important reproductive strategy. Furthermore, a novel behaviour in P. kaupii was documented. We expand the understanding of Gymnophiona biology, in particular of a fully aquatic species, and provide support for future ecological and conservation research on caecilians.

Exploring the Diversity of Bryophytes in Different Forests in the Eastern Amazonia

Exploring the Diversity of Bryophytes in Different Forests in the Eastern Amazonia

Whole genomes show contrasting trends of population size changes and genomic diversity for an Amazonian endemic passerine over the late quaternary.

The "Amazon tipping point" is a global change scenario resulting in replacement of upland terra-firme forests by large-scale "savannization" of mostly southern and eastern Amazon. Reduced rainfall accompanying the Last Glacial Maximum (LGM) has been proposed to have acted as such a tipping point in the past, with the prediction that terra-firme inhabiting species should have experienced reductions in population size as drier habitats expanded. Here, we use whole-genomes of an Amazonian endemic organism (Scale-backed antbirds - Willisornis spp.) sampled from nine populations across the region to test this historical demography scenario. Populations from southeastern Amazonia and close to the Amazon-Cerrado ecotone exhibited a wide range of demographic patterns, while most of those from northern and western Amazonia experienced uniform expansions between 400 kya and 80-60 kya, with gradual declines toward 20 kya. Southeastern populations of Willisornis were the last to diversify and showed smaller heterozygosity and higher runs of homozygosity values than western and northern populations. These patterns support historical population declines throughout the Amazon that affected more strongly lineages in the southern and eastern areas, where historical "tipping point" conditions existed due to the widespread replacement of humid forest by drier and open vegetation during the LGM.

Well-spread samples with dynamic sample sizes.

A spatial sampling design determines where sample locations are placed in a study area so that population parameters can be estimated with relatively high precision. If the response variable has spatial trends, spatially balanced or well-spread designs give precise results for commonly used estimators. This article proposes a new method that draws well-spread samples over arbitrary auxiliary spaces and can be used for master sampling applications. All we require is a measure of the distance between population units. Numerical results show that the method generates well-spread samples and compares favorably with existing designs. We provide an example application using several auxiliary variables to estimate total aboveground biomass over a large study area in Eastern Amazonia, Brazil. Multipurpose surveys are also considered, where the totals of aboveground biomass, primary production, and clay content (3 responses) are estimated from a single well-spread sample over the auxiliary space.