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Search Results: 1 - 10 of 6102 matches for " Renato Cintra "
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Ecological Gradients Influencing Waterbird Communities in Black Water Lakes in the Anavilhanas Archipelago, Central Amazonia
Renato Cintra
International Journal of Ecology , 2012, DOI: 10.1155/2012/801683
Abstract: For the first time, and in a large spatial scale, the influence of ecological properties on the aquatic bird community of black water lakes in Brazilian Amazonia is evaluated. Bird surveys were conducted in 45 lakes. A total of 3626 individuals in 48 bird species were recorded; of these, 31 are aquatic, and 18 of these are primarily piscivorous. Bird richness and abundance were not significantly related to lake shape and productivity but were influenced by hydrological period (low versus high), water depth, transparency, lake isolation, and habitat richness. Matrices of bird species by lake were subjected to multivariate analyses (NMDS) to evaluate how these parameters influence bird community. The variation in bird species composition was positively correlated to lake depth and isolation and negatively correlated to water transparency and habitat richness. The results indicate that period, lake physical characteristics (depth, water transparency), isolation, and habitat richness are determinants of aquatic bird community composition in the black water lake systems of Amazonia.
Ecological Gradients Influencing Waterbird Communities in Black Water Lakes in the Anavilhanas Archipelago, Central Amazonia
Renato Cintra
International Journal of Ecology , 2012, DOI: 10.1155/2012/801683
Abstract: For the first time, and in a large spatial scale, the influence of ecological properties on the aquatic bird community of black water lakes in Brazilian Amazonia is evaluated. Bird surveys were conducted in 45 lakes. A total of 3626 individuals in 48 bird species were recorded; of these, 31 are aquatic, and 18 of these are primarily piscivorous. Bird richness and abundance were not significantly related to lake shape and productivity but were influenced by hydrological period (low versus high), water depth, transparency, lake isolation, and habitat richness. Matrices of bird species by lake were subjected to multivariate analyses (NMDS) to evaluate how these parameters influence bird community. The variation in bird species composition was positively correlated to lake depth and isolation and negatively correlated to water transparency and habitat richness. The results indicate that period, lake physical characteristics (depth, water transparency), isolation, and habitat richness are determinants of aquatic bird community composition in the black water lake systems of Amazonia. 1. Introduction Ecological studies on the composition and structure of biological communities are critical to understanding the interactions between the species and populations that comprise them, to explain local and regional biodiversity [1, 2], and are essential to guiding management actions and conservation policies. Tropical wetlands provide habitats for a wide variety of plants, fishes, birds, and mammals. Aquatic environments (rivers, lakes, and wetlands) represent 6% of Brazilian Amazonia, and over 100,000?km2 of lakes and swamps [3]. Aquatic birds are ubiquitous components of Amazonian freshwater systems. However, their role in the ecological dynamics of these systems has often been overlooked, as in other rainforest areas in the Neotropics (but see [4–6]). In order to evaluate the impacts of human activities on freshwater systems and improve their conservation value, the status and trends of freshwater biodiversity need to be monitored [7]. Because many aquatic birds are top predators in the aquatic environments, they can affect the distribution and abundance of fish [8], and presumably other biota. Both in tropical and temperate wetlands, aquatic bird communities have been demonstrated to be influenced by their environment (lake features such as their degree of isolation, depth, physical-chemical properties, and habitat availability) or/and by their own interaction and population dynamics (see below). For instance, in southern Brazil in fragmented wetlands, it has been
Effects of forest heterogeneity on occurrence and abundance of the scale-backed antbird, Hylophylax poecilinotus (Aves: Thamnophilidae), in the Amazon forest
Cintra, Renato;Cancelli, Jessica;
Revista Brasileira de Zoologia , 2008, DOI: 10.1590/S0101-81752008000400008
Abstract: recently, a significant number of studies on neotropical forest bird communities have focused on factors influencing their richness, abundance, and habitat selection. however, few of them have considered populations or individual species, and how habitat structure affects their distribution and abundance. in this study, we investigated how the combined effects of some forest structure components affect the occurrence and abundance of a resident bird species, the scale-backed antbird hylophylax poecilinotus (cabanis, 1847). we tested the null hypothesis of no difference between the variation in forest structure components at locations where birds occurred and at locations where they did not. in a pristine terra firme forest at the ducke reserve, manaus, we recorded bird occurrence and abundance using mist nets in 56 transects (1 km long each) within a 9 x 9 km trail grid covering 6400 ha. also in the same 56 transects, we set 50 x 50 m plots and recorded the following seven components of forest structure and landscape: 1) canopy opening, 2) leaf litter, 3) tree abundance, 4) logs, 5) snags, 6) streams, and 7) elevation. we evaluated their effects on avian occurrence and abundance by using models of multiple logistic regression (for bird occurrence) and multiple linear regression (for bird abundance). the results suggested that h. poecilinotus occurred significantly more often in lowland areas, in areas located farther away from streams, and in areas bearing thicker leaf litter. hylophylax poecilinotus was also more abundant in lowland areas and in areas located further away from streams. overall, the results indicated that environmental heterogeneity produced by variation in forest structure components affects habitat use by this bird species in the amazon forest.
Spatial Variation in Bird Community Composition in Relation to Topographic Gradient and Forest Heterogeneity in a Central Amazonian Rainforest
Renato Cintra,Luciano N. Naka
International Journal of Ecology , 2012, DOI: 10.1155/2012/435671
Abstract: We investigated the effects of landscape features and forest structure on the avian community at the Reserva Florestal Adolpho Ducke near Manaus, in the Brazilian Amazon. We sampled the landscape and forest in 72 50 × 50 m plots systematically distributed in the reserve, covering an area of 6,400 ha. The avifauna was sampled using mist nets and acoustic surveys near the plots. We found no significant relationships between landscape features and forest components in the plots and the number of bird species and individuals sampled. Results of Principal Coordinate Analyses, however, showed that bird species composition changes along a topographic gradient (plateau-slope-valley), and also in relation to leaf litter depth and distance to forest streams. We also found compositional differences in the avian community on the eastern and western water basins that compose the reserve. Our results suggest that although most bird species occur throughout the reserve, many species track differences in the landscape and the forest structure.
Effects of forest structure components on the occurence, group size and density of groups of bare-face tamarin (Saguinus bicolor - primates: Callitrichinae) in Central Amazonia
Vidal, Marcelo Derzi;Cintra, Renato;
Acta Amazonica , 2006, DOI: 10.1590/S0044-59672006000200014
Abstract: this study analyzed the influence of forest structural components on the occurence, size and density of groups of bare-face tamarin (saguinus bicolor) - the most threatened species in the amazon - and produced the first map of distribution of groups in large-scale spatial within the area of continuous forest. population censuses were conducted between november 2002 and july 2003, covering 6400 hectares in the ducke reserve, manaus-am, brazil. groups of s. bicolor were recorded 41 times accordingly distributed in the environments: plateau (20); slopes (12); and lowlands (09). the mean group size was 4.8 indiv./group, and ranged from 2 to 11 individuals. in the sites where the groups were recorded, and in an equivalent number of sites where no tamarins were found located at least 500 m from those where they had been recorded, we placed 50 m x 50 m plots to record the following forest structural components: abundance of trees; abundance of lianas; abundance of fruiting trees and lianas; abundance of snags; abundance of logs; percentage of canopy opening; leaf litter depth; and altitude. bare-face tamarin more often uses areas with lower abundance of forest logs, smaller canopy opening and with higher abundance of snags, areas in the forest with smaller canopy opening present higher density of s. bicolor groups. apparently this species does not use the forest in a random way, and may select areas for its daily activities depending on the micro-environmental heterogeneity produced by the forest structural components.
The effects of forest structure on occurrence and abundance of three owl species (Aves: Strigidae) in the Central Amazon forest
Barros, Obed G.;Cintra, Renato;
Zoologia (Curitiba) , 2009, DOI: 10.1590/S1984-46702009000100014
Abstract: we investigated how forest structure affects the occurrence and abundance of three owl species: the crested owl lophostrix cristata daudin, 1800, the amazon pygmy owl glaucidium hardyi vielliard, 1990, and the tawny-bellied screech owl megascops watsonii cassin, 1849. we surveyed the owls mostly between 07:00 and 11:00 pm from july 2001 to april 2002, in eighteen 8 km transects along trails at the ducke reserve, manaus, central amazon, brazil. we staked out 50 x 50 m plots where the presence and absence of the owls were recorded. we compared some components of the forest structure between plots where owls were present and plots where they were absent. the spatial variation in these components were related to the occurrence and abundance of the owls using models of multiple logistic and multiple linear regressions analysis, respectively. lophostrix cristata is rare in many other areas of the amazon forest, but it was the most abundant in our study area. lophostrix cristata and g. hardyi were more concentrated along the uplands (central plateau), which divide the reserve into two drainage water-basins. megascops watsonii was distributed mainly in the southeastern part of the reserve. glaucidium hardyi was more often found in areas with larger canopy openness. in areas with higher abundance of snags, there was significantly higher occurrence of l. cristata and m. watsonii. megascops watsonii was also more abundant in areas with higher abundance of forest trees and in areas bearing shallower leaf litter on the forest floor. this study is the first to analyze at large spatial scale the effects of forest structure on neotropical forest top predator nocturnal birds. the results indicate that forest structure can affect the occurrence and abundance of owls in the amazon forest.
Spatial Variation in Bird Community Composition in Relation to Topographic Gradient and Forest Heterogeneity in a Central Amazonian Rainforest
Renato Cintra,Luciano N. Naka
International Journal of Ecology , 2012, DOI: 10.1155/2012/435671
Abstract: We investigated the effects of landscape features and forest structure on the avian community at the Reserva Florestal Adolpho Ducke near Manaus, in the Brazilian Amazon. We sampled the landscape and forest in 72 50 × 50?m plots systematically distributed in the reserve, covering an area of 6,400?ha. The avifauna was sampled using mist nets and acoustic surveys near the plots. We found no significant relationships between landscape features and forest components in the plots and the number of bird species and individuals sampled. Results of Principal Coordinate Analyses, however, showed that bird species composition changes along a topographic gradient (plateau-slope-valley), and also in relation to leaf litter depth and distance to forest streams. We also found compositional differences in the avian community on the eastern and western water basins that compose the reserve. Our results suggest that although most bird species occur throughout the reserve, many species track differences in the landscape and the forest structure. 1. Introduction Understanding how the structure of the habitat influences avian populations and communities is a key factor to link habitat and niche selection with species diversity [1, 2]. Although the mechanisms that determine habitat use in tropical forests remain poorly understood [3, 4], it is clear that different species use their surrounding environment differently. This use can change over space and time due to individual movements, but also as a result of differences in habitat structure [5–9]. Several studies have focused on the factors affecting avian species richness and abundance in tropical forests, investigating the relationship between vegetation structure and bird communities [2, 8–10], but few have investigated how natural variations in the structure of the forest may affect entire species assemblages (but see [4, 7, 11]). When available, such studies are often done at small spatial scales [9, 12, 13], and the effects of habitat structure are rarely considered. Most bird species in Amazonia are resident and sedentary [12, 14, 15], and are relatively long-lived compared to those in temperate regions [16]. Longevity can result in a more specialized use of the environment, and birds may adjust their microhabitat use according to local variation in the forest structure [7, 11, 17]. Avian community composition, microhabitat selection, and guild assemblages can be affected by landscape features such as elevation, topography (valleys, slopes, and plateaus), and proximity to water. Furthermore, the natural
Abundance of two Dendrocincla woodcreepers (aves: Dendrocolaptidae) in relation to forest structure in Central Amazonia
Cintra, Renato;Maruoka, Adrianny Erika;Naka, Luciano Nicolas;
Acta Amazonica , 2006, DOI: 10.1590/S0044-59672006000200011
Abstract: few studies have been conducted to verify how the structure of the forest affects the occurence and abundance of neotropical birds. our research was undertaken between january 2002 and july 2004 at the reserva ducke, near manaus (02o55',03o01's; 59o53',59o59'w) in central amazonia, to verify how the forest structure affects the occurrence and abundance of two bird species: the plain-brown woodcreeper dendrocincla fuliginosa and the white-chinned woodcreeper dendrocincla merula. bird species occurrence was recorded using lines of 20 mist-nets (one sample unit), along 51 1-km transects distributed along 9 pararel 8 km trails covering an area of 6400 ha. along these transects, we placed 50 x 50m plots where we recorded forest structure components (tree abundance, canopy openness, leaf litter, standing dead trees, logs, proximity to streams, and altitude). we then related these variables to bird occurence and abundance using multiple logistic and multiple linear regression models, respectively. we found that d. fuliginosa frequently used plateau areas; being more abundant in areas with more trees. on the other hand, d. merula occurred more frequently and was more abundant in areas with low tree abundance. our results suggest that although both species overlap in the reserve (both were recorded in at least 68% of the sampled sites), they differ in the way they use the forest microhabitats. therefore, local variation in the forest structure may contribute to the coexistence of congeneric species and may help to maintain local alpha diversity.
Asynchronous Realization of Algebraic Integer-Based 2D DCT Using Achronix Speedster SPD60 FPGA
Nilanka Rajapaksha,Amila Edirisuriya,Arjuna Madanayake,Renato J. Cintra
Journal of Electrical and Computer Engineering , 2013, DOI: 10.1155/2013/834793
Abstract:
VLSI Architecture for 8-Point AI-based Arai DCT having Low Area-Time Complexity and Power at Improved Accuracy
Amila Edirisuriya,Arjuna Madanayake,Vassil S. Dimitrov,Renato J. Cintra,Jithra Adikari
Journal of Low Power Electronics and Applications , 2012, DOI: 10.3390/jlpea2020127
Abstract: A low complexity digital VLSI architecture for the computation of an algebraic integer (AI) based 8-point Arai DCT algorithm is proposed. AI encoding schemes for exact representation of the Arai DCT transform based on a particularly sparse 2-D AI representation is reviewed, leading to the proposed novel architecture based on a new final reconstruction step (FRS) having lower complexity and higher accuracy compared to the state-of-the-art. This FRS is based on an optimization derived from expansion factors that leads to small integer constant-coefficient multiplications, which are realized with common sub-expression elimination (CSE) and Booth encoding. The reference circuit [1] as well as the proposed architectures for two expansion factors α? = 4.5958 and α′ = 167.2309 are implemented. The proposed circuits show 150% and 300% improvements in the number of DCT coefficients having error ≤ 0:1% compared to [1]. The three designs were realized using both 40 nm CMOS Xilinx Virtex-6 FPGAs and synthesized using 65 nm CMOS general purpose standard cells from TSMC. Post synthesis timing analysis of 65 nm CMOS realizations at 900 mV for all three designs of the 8-point DCT core for 8-bit inputs show potential real-time operation at 2.083 GHz clock frequency leading to a combined throughput of 2.083 billion 8-point Arai DCTs per second. The expansion-factor designs show a 43% reduction in area (A) and 29% reduction in dynamic power (PD) for FPGA realizations. An 11% reduction in area is observed for the ASIC design for α? = 4.5958 for an 8% reduction in total power ( PT ). Our second ASIC design having α′ = 167.2309 shows marginal improvements in area and power compared to our reference design but at significantly better accuracy.
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