Southwestern Brazilian Amazonia Research Articles

Bat-Associated Pathogenic Leptospira spp. from Forest Fragments in Southwestern Brazilian Amazonia

Bats are known as potential carriers of different pathogens; these animals have been identified worldwide as an important reservoir of different species of Leptospira. Therefore, there has been an increasing interest in studying leptospirosis in neotropical bats in the Amazon. This region is a fertile ground for zoonotic diseases, given the intense process of deforestation, urbanization, opening of new agricultural frontiers, predatory hunting, effects of climate change, and loss of biodiversity. Based on this, the aim of the present study was to investigate the frequency of infection associated with the genetic characterization of pathogenic Leptospira spp. in bats inhabiting diverse landscapes in the southwestern region of the Amazon. To conduct the study, mist nets were installed to capture bats. Kidney samples were submitted to LipL32-polymerase chain reaction and secY gene sequencing. Our results showed that 21% of neotropical evaluated bats in Southwestern Amazon were infected with Leptospira spp. Positive animals were found in rural, urban, periurban, and control areas. Sanguinivores had the highest frequency of positives, followed by insectivores and frugivorous bats. The species of L. interrogans and a potential new Leptospira species were identified. The frequency of Leptospira in bats was not influenced by landscape type, suggesting these pathogens may not be affected by landscape changes. The findings suggest that bats may serve as potential reservoirs of Leptospira in diverse landscapes. The presence of Leptospira in bats appears to be independent of the type of land use, implying that these pathogens may not be affected by small-scale changes in the environment.

A new pale-ventered nurse frog (Aromobatidae: Allobates) from southwestern Brazilian Amazonia

Abstract We use integrative taxonomy to formally describe a candidate species of nurse frog of the genus Allobates from southwestern Brazilian Amazonia. The new species nests within a clade that has been defined historically as A. gasconi, but it has an 8.8–11.0% genetic distance for 16S to samples from the type locality of A. gasconi. The new species differs from congeners mainly by males having a translucent white throat and vocal sac; advertisement calls with a duration of 42–60 ms, two notes separated by an inter-note interval of 8–23 ms, and a dominant frequency of 4,953–6,331 Hz; and exotrophic tadpoles with 2 pyramidal papillae on each end of the upper lip and 10–13 pyramidal and cylindrical papillae surrounding the lower lip. Phylogenetic analyses based on mitochondrial DNA suggest that A. gasconi sensu lato as defined previously represents a complex of as many as seven species, corroborating studies that have shown high levels of cryptic diversity within Allobates.

The advertisement call of Allophryne resplendens (Anura: Allophrynidae) from southwestern Brazilian Amazonia.

The advertisement call of Allophryne resplendens (Anura: Allophrynidae) from southwestern Brazilian Amazonia.

Fossil frogs from the upper Miocene of southwestern Brazilian Amazonia (Solimões Formation, Acre Basin).

ABSTRACT Much of what we know about late Miocene vertebrates from the Brazilian Amazonia is based on the fossil record from several sites in the Solimões Formation. The Talismã site, one of the most important for vertebrate fossils in the formation, has produced an abundant and diverse fauna dominated by crocodylians, mammals, and turtles, but small vertebrates are still underrepresented. We report some isolated bones recovered from this site, providing the first Neogene records of anurans in Brazil. Two taxa are recognized, a distinct species of Pipa, and an unidentified species of the Rhinella clade, both of which are members of the extant Amazonian batrachofauna. These new fossils expand our knowledge of the late Miocene anuran assemblages from the region and contribute to the paleoenvironmental reconstruction of the site.

Habitat Quality, Not Patch Size, Modulates Lizard Responses to Habitat Loss and Fragmentation in the Southwestern Amazon

As deforestation frontiers expand in the tropics, understanding species responses is critical to inform efficient land-use management policies. Here we evaluated lizard responses to changes in landscape, habitat patch, and quality in a deforestation frontier in southwestern Brazilian Amazonia. We first considered overall lizard assemblages and then two species subgroups of contrasting thermoregulation strategies. We sampled lizards at 21 forest patches (42–7,035 ha) subject to moderate habitat disturbance (e.g., cattle intrusion and selective logging). Based on 6,000 pitfall trap-days and 60,000 m of visual surveys, we recorded 215 individuals representing 15 species. Contrary to expectations, species richness and abundance were not explained by any of the variables considered, including matrix quality, proportion of forest cover, forest patch area and shape, age since isolation, arthropod biomass, canopy openness, litter volume, tree density, and fire history. However, the composition of persisting species was determined by the structural complexity of the adjacent matrix. The abundance of species that avoid direct sun exposure to regulate their body temperature increased under more-complex structures of adjacent matrix areas and decreased within patches more intensively affected by past fire events. Disturbance within forest patches likely decreased the patch-matrix contrast, contributing to the absence of forest area effects. Nevertheless, species-specific microhabitat requirements dictated part of the lizard species that were able to persist in the fragmented landscape. Strategies aiming to maximize lizard diversity should embrace retention of the habitat quality within forest patches and forest corridors/high-stature vegetation in at least some sites connecting forest remnants.

A NEW SPECIES OF OSTEOCEPHALUS STEINDACHNER, 1862 (ANURA, HYLIDAE), FROM BRAZILIAN AMAZONIA

Treefrogs of the genus Osteocephalus have been the focus of several taxonomic and phylogenetic studies, especially in the last two decades. These recent studies have shown that the diversity of this charismatic Amazonian genus is still largely underestimated. Through the evidence of morphological and molecular data, we describe a new species of the Osteocephalus alboguttatus species group from the Purus-Madeira Interfluve, southwestern Brazilian Amazonia. The new species differs from other Osteocephalus by having a small body size (snout–vent length 32.1–44.1 mm), skin texture non-sexually dimorphic, dorsum smooth with a few scattered small tubercles, vocal sac single and subgular, frontoparietal ridges not externally visible, and a dark tan brown iris with lighter vermiculation. The rapid increase in the number of new frog species described from the Purus-Madeira Interfluve highlight the importance of sampling poorly explored and remote areas in Amazonia, as well as the value of supporting taxonomic research to accelerate species documentation in face of the biodiversity crisis.

Orchid bees in riparian and terra-firme forest fragments in an urban matrix in southwestern Brazilian Amazonia

ABSTRACT Riparian forests are important ecosystems that support an enormous biodiversity in Brazil. Despite being protected under Brazilian legislation, these forests suffer great impact from the fragmentation of habitats. Orchid bees are a key group of pollinators in the Neotropical region, yet few data are available on the assamblage structure of these bees in riparian forests. We evaluated the role of fragments of riparian and terra-firme forest on the conservation and maintenance of orchid bees in an urban landscape in the southwestern Amazon basin. Specifically, we evaluated whether bee assemblages in riparian and terra-firme forests differed significantly in abundance, species richness and composition. We also evaluated whether species richness and abundance of bees vary with the size of the forest fragment. Male bees were attracted using odoriferous baits and collected with entomological nets in 10 forest fragments. There was no significant difference between riparian and terra-firme fragments in species abundance, richness and composition, but there was a positive correlation between fragment size and species richness and abundance. Our results suggest that, in an urban landscape, the remaining riparian and terra-firme forest fragments still could maintain 62.7% of the orchid bee species known to occur in the region, reinforcing the conservation value of these forest remnants. Our findings indicate that these fragments provide a potentially important habitat for the maintenance of local bee populations in the landscape.

Growth Assessment of Native Tree Species from the Southwestern Brazilian Amazonia by Post-AD 1950 14C Analysis: Implications for Tropical Dendroclimatology Studies and Atmospheric 14C Reconstructions

Tree-ring width chronologies of cedro (Cedrela fissilis Vell.) (1875 to 2018), jatobá (Hymenaea courbaril L.) (1840 to 2018) and roxinho Peltogyne paniculata Benth.) (1910 to 2018) were developed by dendrochronological techniques in the southern Amazon Basin. Acceptable statistics for the tree-ring chronologies were obtained, and annual calendar dates were assigned. Due to the lack of long-term chronologies for use in paleoclimate reconstructions in degraded forest areas, dendrochronological dating was validated by 14C analysis. Tree-rings selected for analysis corresponded to 1957, 1958, 1962, 1963, 1965, 1971, and 1972. Those are critical calendar years in which atmospheric 14C changes were the highest, and therefore their tree-ring cellulose extracts 14C signatures when in alignment with existing post-AD 1950 atmospheric 14C atmospheric curves would indicate annual periodicity. Throughout our correlated calendar years and post-AD 1950 14C signatures, we indicate that H. courbaril shows an erratic sequence of wood ages. The other two tree species, C. fissilis and P. paniculata, are annual in nature and can be used successfully as paleoclimate proxies. Moreover, due to the sampling site’s strategic location in relation to the Tropical Low-Pressure Belt over South America, these trees can be used to enhance the limited amount of observational data in Southern Hemisphere atmospheric 14C calibration curves.

Structure and Home Range Size of Mixed-Species Bird Flocks in a Bamboo Forest in Southwestern Amazonia

Mixed-species flocks of birds are cohesive groups of two or more different species that are kept in formation by systematic behavioral interactions among the members of the flocks. Typically, mixed-species flocks form themselves around a nuclear species, which presents a specific pattern of movement during foraging, and a song that is recognized by the other species. In the understory of Neotropical forests, representatives of the family Thamnophilidae, in particular species of the genus Thamnomanes, have become adapted for the role of nuclear species in mixed-species flocks. In the present study, we describe the mixed-species flocks led by individuals of Bluish-slate Antshrike Thamnomanes schistogynus in a forest dominated by bamboo Guadua sp. in southwestern Brazilian Amazonia. We collected data within a 600 × 600 m grid subdivided into 36 1-ha plots, with a total area of 36 ha. Within this grid, we delimited the home ranges and core areas of the resident mixed-species flocks. We also identified the composition of each flocks, frequency, fidelity of its members and determined the relationship between mixed-species flocks and vegetation structure within the grid. We delimited the home ranges of eight mixed-species flocks. The mean home range, estimated using the Minimum Convex Polygon method, was 3.45 ± 0.17 ha, and estimated using the autocorrelated kernel density estimation method was 3.65 ± 0.15 ha, and the mean core area, 1.14 ± 0.03 ha. The home ranges of the mixed-species flocks led by T. schistogynus in southwestern Amazonia are among the smallest recorded in species of the genus Thamnomanes. We identified 71 different bird species in the mixed-species flocks with a mean of 41.1 ± 2.1. While the geographic distribution of the lead species T. schistogynus coincides almost exactly with that of the bamboo forests of southwestern Amazonia, our results did not indicate any systematic relationship or fidelity between the mixed-species flocks led by this species and the bamboo forest.

Mammal responses to reduced-impact logging in Amazonian forest concessions

Production forests are a dominant feature of most tropical forest landscapes and it is therefore important to understand the effects of timber extraction on the resident fauna. Here we investigate the effects of reduced-impact logging (RIL) on medium- to large-sized terrestrial mammals in two Jamari National Forest logging concessions, south-western Brazilian Amazonia. We used camera traps to survey the terrestrial mammal fauna. Bayesian multi-species occupancy models (MSOMs) were performed to assess the effect of logging intensity and density of logging roads on site-level species richness, occupancy and detection rates. Species richness was negatively affected by logging status and by increasing logging intensity, and positively affected by road density. Occupancy and detection rates of individual species were largely unrelated to model predictors, although responses across species tended to be consistent with that observed for species richness. Despite negative effects of logging on species richness, no individual species were lost at the landscape level, suggesting that concessions managed under RIL techniques may be a reasonable compromise between economic and conservation interests.

Degree of Frugivory Predicts Rates of Food-Related Agonism and Intragroup Proximity in Wild Gray Woolly Monkeys (Lagothrix lagotricha cana).

The main factors influencing feeding competition among members of diurnal primate groups are the distribution, availability, and quality of food resources. Socioecological models predict that temporal availability of preferred resources, such as fruit, can influence intragroup feeding competition, which is expected to affect rates of agonism and intragroup spatial patterns. We evaluated the effects of temporal variation in fruit availability on the degree of frugivory (i.e., the proportion of time spent feeding on fruit in relation to total food consumption) and the effects of fruit availability and degree of frugivory on rates of agonistic interactions, and intragroup proximity in two wild groups of gray woolly monkeys (Lagothrix lagotricha cana) in southwestern Brazilian Amazonia. We recorded 227 agonistic interactions via the all occurrences method and 3549 records of spacing via scan sampling during an 8-mo field study from March to October 2017. We found that fruit availability showed a positive relationship with the woolly monkeys’ degree of frugivory, which in turn showed a positive relationship with the rates of agonism. We also found that degree of frugivory positively affected intragroup proximity in periods of lower fruit availability, and that agonistic interactions and proximity covaried positively. Conversely, as the degree of frugivory increased, monkeys exhibited greater interindividual distances and, consequently, lower rates of agonism, consistent with lower levels of feeding competition in periods of higher fruit availability. Therefore, we suggest that intragroup contest competition for fruits is an important cost of group living even for generalized, opportunistic frugivorous primates, such as woolly monkeys.

Burning in southwestern Brazilian Amazonia, 2016–2019

Fire is one of the most powerful modifiers of the Amazonian landscape and knowledge about its drivers is needed for planning control and suppression. A plethora of factors may play a role in the annual dynamics of fire frequency, spanning the biophysical, climatic, socioeconomic and institutional dimensions. To uncover the main forces currently at play, we investigated the area burned in both forested and deforested areas in the outstanding case of Brazil's state of Acre, in southwestern Amazonia. We mapped burn scars in already-deforested areas and intact forest based on satellite images from the Landsat series analyzed between 2016 and 2019. The mapped burnings in already-deforested areas totalled 550,251 ha. In addition, we mapped three forest fires totaling 34,084 ha. Fire and deforestation were highly correlated, and the latter occurred mainly in federal government lands, with protected areas showing unprecedented forest fire levels in 2019. These results indicate that Acre state is under increased fire risk even during average rainfall years. The record fires of 2019 may continue if Brazil's ongoing softening of environmental regulations and enforcement is maintained. Acre and other Amazonian states must act quickly to avoid an upsurge of social and economic losses in the coming years.

Birds associated with treefall gaps in a lowland forest in southwestern Brazilian Amazonia

ABSTRACT Natural communities are dynamic systems in time and space. The spatial distribution of plants and animals tends to coincide with the availability of resources needed for the survival and reproduction of each species. Natural treefall gaps offer a number of resources that influence the distribution of birds within the forest. We compared the understory bird assemblages of natural treefall gaps (15 sampling points) with those found in the adjacent forest (15 points) in the Humaitá Forest Reserve in southwestern Brazilian Amazonia. We used mist-nets to sample birds and obtained 700 captures of 105 species. Species richness, number of individuals, and species composition were all similar between gaps and forest, although six species presented some degree of association with the gaps, and nine with the forest. Nectarivores preferred gaps significantly over forest, whereas insectivores and frugivores were distributed equally between gaps and forest. Vegetation height and density differed between gaps and forest, and influenced the distribution of bird species in the two environments. Fruit availability was positively correlated with frugivore abundance in gaps. Overall, 33.3% of the birds associated with the treefall gaps are from lower forest canopy, while the others are understory species. We showed that the use of natural gaps by birds in a fragmented landscape of the Amazon forest contributes to the environmental heterogeneity and succession dynamics following natural events of habitat disturbance.

Terrestrial gastropods of Humaitá Forest Reserve, southwestern Brazilian Amazon

The molluscan fauna of southwestern Brazilian Amazonia is poorly known due to the lack of focused collection areas in the region since the early 20th century. The present study provides an inventory of the terrestrial gastropods from a forest fragment in the eastern Acre state, Brazil: the Humaitá Forest Reserve (“Reserva Florestal Humaitá”). Live specimens and empty shells were collected between August 2018 and January 2019. A total of 20 species were identified, distributed in 11 families. Most (13) of these species were recorded in Acre for the first time. Furthermore, we confirm the occurrence of Systrophia helicycloides (d’Orbigny, 1835) in Brazil, reiterate the synonymy of Plekocheilus pentadinus (d’Orbigny, 1835) with P. floccosus (Spix in Wagner, 1827), and synonymize Solaropsis peruviana Haas, 1951 with S. juruana Ihering, 1905.

A new nurse frog (Anura: Allobates) from Brazilian Amazonia with a remarkably fast multi-noted advertisement call.

Nurse frogs (Aromobatidae: Allobates) are probably the most extensively studied genus by taxonomists in Brazilian Amazonia. The southwestern portion of Amazonia is the most species-rich: as many as seven species may occur in sympatry at a single locality. In this study, we describe a new species of nurse frog from this region. The description integrates data from larval and adult morphology, advertisement calls and DNA sequences. Allobates velocicantus sp. nov. is distinguished from other Allobates mainly by the absence of hourglass-shaped dark marks on the dorsum and dark transverse bars on the thigh; a throat that is white centrally and yellow marginally; basal webbing on toes II and III; finger I longer than finger II; and an advertisement call composed of 66–138 pulsed notes with a note duration of 5–13 ms, inter-note intervals of 10–18 ms and a dominant frequency of 5,512–6,158 Hz. Tadpoles of the new species have 3–4 short, rounded papillae on the anterior labium, 16–23 papillae on the posterior labium, and a labial keratodont row formula 2(2)/3(1). This is the fifth species of Allobates described from the state of Acre, southwestern Brazilian Amazonia.

Entrelaçado, a rare maize race conserved in Southwestern Amazonia

Maize (Zea mays spp. mays L.) is the major domesticated cereal of the Americas and is of great relevance for global food security. For a long time, Amazonia represented an empty space in the racial distribution maps of this species, due to the lack of collections and the idea that locally developed races became extinct during European colonization. However, a native race had been described in Brazilian Amazonia, the Entrelacado race, and a new study placed Amazonia on the map again, with a proposal for a center of diversification in Southwestern Amazonia. We prospected maize in the Brazilian states of Acre and Rondonia (Southwestern Brazilian Amazonia) and found floury landraces belonging to the Entrelacado race, rare in existing collections and often considered extinct in the field. We collected indigenous and local names, general and specific uses for Entrelacado, and characterized these accessions to compare them with other Brazilian floury maize races, based on data from the literature. Floury maize from the Southwest formed a coherent group in the cluster analysis, which grouped with Entrelacado from the literature, confirming its identification and demonstrating that this race is conserved in Southwestern Amazonia.

Bird-plant interactions on the edge of a forest fragment in southwestern Brazilian Amazonia

Seed dispersal is one of the principal ecological processes that determine the richness and distribution of plants in tropical forests. Birds play an important role in the zoochoric dispersal of seeds in these forests. The present study investigated the bird-plant interactions involving the ingestion and dispersal of seeds by the birds found in the edge habitat of an isolated forest fragment on the Catuaba Experimental Farm in eastern Acre, in southwestern Brazilian Amazonia. The birds were captured using mist nets, and the seeds were collected from fecal samples obtained during the handling of the animals. These seeds were sorted and identified. The bird and the plant species identified during the study were used to calculate the connectivity and nestedness of the bird-plant interactions. We captured 82 species of birds, with a total sampling effort of 203,180 h.m². Fecal samples obtained from 19 of the bird species contained a total of 2,086 seeds, representing 23 plant species. The interaction network had an intermediate connectance, and significant nestedness. Ramphocelus carbo had the highest importance index and was the bird with the largest number of plant interactions, while Cecropia latiloba was the plant with the highest importance index, followed by Schefflera morototoni. Most of the seed-dispersing birds identified in the present study are generalists found in both the forest core and its edge. The results of the study indicated that the community of generalist-frugivore birds interacts extensively with the plant community of the fragment, providing seed dispersal services that include the deforested areas adjacent to the fragment.

Hierarchical effects of historical and environmental factors on lizard assemblages in the upper Madeira River, Brazilian Amazonia.

Investigating the role of historical and ecological factors structuring assemblages is relevant to understand mechanisms and processes affecting biodiversity across heterogeneous habitats. Considering that community assembly often involves scale-dependent processes, different spatial scales may reveal distinct factors structuring assemblages. In this study we use arboreal and leaf-litter lizard abundance data from 83 plots to investigate assemblage spatial structure at two distinct scales in southwestern Brazilian Amazonia. At a regional scale, we test the general hypothesis that the Madeira River acts as a barrier to dispersal of some lizard species, which results in distinct assemblages between river banks. At a local scale, we test the hypothesis that assemblages are not evenly distributed across heterogeneous habitats but respond to a continuum of inadequate-to-optimal portions of environmental predictors. Our results show that regional lizard assemblages are structured by the upper Madeira River acting as a regional barrier to 29.62% of the species sampled. This finding suggests species have been historically isolated at one of the river banks, or that distinct geomorphological features influence species occurrence at each river bank. At a local scale, different sets of environmental predictors affected assemblage composition between river banks or even along a river bank. These findings indicate that environmental filtering is a major cause of lizard assemblage spatial structure in the upper Madeira River, but predictor variables cannot be generalized over the extensive (nearly 500 km) study area. Based on a single study system we demonstrate that lizard assemblages along the forests near the banks of the upper Madeira River are not randomly structured but respond to multiple factors acting at different and hierarchical spatial scales.

Palm distribution patterns in the southwestern Brazilian Amazon: Impact of a large hydroelectric dam

Mega hydroelectric dams cause loss of habitat for many species and lead to local or regional extinction. Despite these dire facts, little is known about the impact of these mega-dams on Amazonia. Using palms as a model, we investigated this question by sampling 26 1-ha plots distributed in the influence areas of the Jirau mega-dam in southwestern Brazilian Amazonia. We examined palm community patterns and species distributions as a function of environmental variables, as well as the effect of this large dam on plant survival. Palm communities on the banks of the Madeira River differ among three main habitats sampled (campinarana, terra-firme and várzea forests), and these differences are associated with the gradient of C, pH, N, P, soil texture, slope, and depth to the water-table. The level of the Madeira River raised after the construction of the Jirau mega-dam, directly affecting the populations of 61.3% of the palm species, particularly those species associated to areas with silty soils, low slope, and low depth to the water-table. Várzea and terra-firme forests near the river, as well as low-lying plots, even those distant from the river, were affected by the filling of the reservoir. Várzea forests and campinaranas had a greater proportion of palm species flooded by the reservoir and the reduction of water-table depth. Várzea forests and campinaranas harbor distinct palm communities from the terra-firme forests and require priority in conservation policies and management to mitigate harmful environmental impacts in the Amazon.

Effects of tropical forest conversion on soil and aquatic systems in southwestern Brazilian Amazonia: A synthesis

Southwestern Brazilian Amazonia has suffered intense forest conversion in a short period of time (~60 years) and deforestation is ongoing. Around 70% of the deforested area has been designated for cattle ranching. This forest clearing and pasture establishment is abruptly disrupting the functioning of the ecosystem. In this paper, we provide an overview of the effects of land conversion from forest to pasture on the soil and aquatic systems. Forest conversion to pasture has two clear effects: a) an on-site effect on the hillslope domain and 2) an off-site effect on the river system. The conversion of forest to pasture affects the soil physical–chemical properties, soil carbon content, water resources, and aquatic system. However, many of these changes are not straightforward or obvious. For example, in some conditions, the soil carbon stock increases in pasture. Despite the advances in our understanding of the effects of land conversion on environmental processes, knowledge gaps persist, and we identify some research needs.