Composição florística e cobertura vegetal das savanas na região de Alter do Chão, Santarém - PA

In this study, we determined the floristic composition in 38 plots of 3.75 ha (250 m x 150 m) distributed throughout 30.000 ha of savannas of "Alter do Chão", Santarém Municipality. Our surveys revealed 130 species in 45 families. The only species of dicotoledons that covered 1% or more of the area in the herb-shrub layer were Dioclea bicolor Benth. and Lafoensia pacari A. St.-Hil. Most of the area was covered by the grasses Paspalum carinatum Humb. & Bonpl. ex Flügge (16%) and Trachypogon plumosus (Humb. & Bonpl. ex Willd.) Nees (22%). The grass Axonopus canescens (Nees ex Trin.) Pilg. and the sedge Rhyncospora hirsuta Vahl also covered slightly more than 1% of the area. Only eight species, Anacardium occidentale L., Himatanthus fallax (Müll. Arg.) M. M. Plumel, Lafoensia pacari A. St.-Hil., Byrsonima coccolobifolia Kunth, Byrsonima crassifolia (L.) Kunth, Pouteria ramiflora (Mart.) Radlk., Qualea grandiflora Mart. and Salvertia convallariodora A. St.-Hil. had canopies in the tree layer which projected over more than 1% of the area. Of these, only B. crassifolia (5.7%), S. convallariodora (6.0%) and P. ramiflora (2.1%) projected over more than 2% of the area. Most of the area (mean = 53%) did not have any grass, bush or sedge cover and 45% also had no tree-canopy cover. Grasses and sedges covered a mean of 39.2% of the plots, and shrubs 11.0%. The correlations between similarity matrices based on species in different vegetation strata and taxonomic groups were generally low and there was little correlation between matrices based on quantitative data and matrices based on presence/absence. Therefore, caution should be exercised in comparisons among savanna areas based on only one vegetative stratum or on only one taxonomic group

Modelagem do crescimento do tambaqui (Colossoma macropomum Cuvier, 1816): Seleção de modelos e inferência multimodelos

The tambaqui, Colossoma macropomum, is one of the most commercially valuable Amazonian fish species, and in the floodplains of the region, they are caught in both rivers and lakes. Most growth studies on this species to date have adjusted only one growth model, the von Bertalanffy, without considering its possible uncertainties. In this study, four different models (von Bertalanffy, Logistic, Gompertz and the general model of Schnüte-Richards) were adjusted to a data set of fish caught within lakes from the middle Solimões River. These models were adjusted by non-linear equations, using the sample size of each age class as its weight. The adjustment evaluation of each model was based on the Akaike Information Criterion (AIC), the variation of AIC between the models (Δi) and the evidence weights (wi). Both the Logistic (Δi = 0.0) and Gompertz (Δi = 1.12) models were supported by the data, but neither of them was clearly superior (wi, respectively 52.44 and 29.95%). Thus, we propose the use of an averaged-model to estimate the asymptotic length (L∞). The averaged-model, based on Logistic and Gompertz models, resulted in an estimate of L∞=90.36, indicating that the tambaqui would take approximately 25 years to reach average size

Efeito do isolamento e das variáveis ambientais na estrutura de comunidades de peixes do interflúvio madeira-purus na amazônia Brasileira

Due to the existence of terrestrial barriers to freshwater fish dispersion, it is believed that its distribution is strongly associated with historical factors related to the formation of the habitats they occupy. By the other hand, some studies reveal the influence of abiotic conditions (such as size of water bodies, pH, conductivity) on the composition of fish fauna occurring in small streams. This study aimed to investigate whether drainage basins, because catchment boundaries are potential barriers to fish dispersion, or the physical structure and physico-chemical characteristics of water have a greater influence on fish community structure in small streams. We sampled 22 streams belonging to five drainage basins in the Madeira-Purus interfluve. Fish were caught with dip nets and a small trawl, and data were simultaneously obtained on structural characteristics of the streams and physico-chemical characteristics of the water. Community composition was analyzed using Non-Metric Multidimensional Scaling (NMDS), and variables related to structural and physico-chemical characteristics were summarized by Principal Component Analysis (PCA). Two explanatory models relating faunal composition to environmental factors were constructed: the first using only continuous variables and the second including the drainage basin as a categorical variable. The Akaike Information Criterion (AIC) and AIC weight were used to select the best model. Although structural and physico-chemical variables significantly contributed to explaining faunal composition, the model including the drainage basin was clearly the better of the two models (more than 90% support in the data). The importance of drainage basins in structuring fish communities in streams may have significant consequences for conservation planning in these environments

The fish fauna of streams in the madeira-purus interfluvial region, Brazilian Amazon

Small headwaters streams of the Neotropical region usually have high species richness and diversity. This study aimed to investigate the species composition and abundance of fish fauna in the headwaters streams of the Madeira-Purus interfluvial plain in the Brazilian Amazon. A total of 22 streams of 1st to 3rd order were sampled during two expeditions at two separate locations in April-May and July of 2007. A total of 5508 fishes were captured using hand and small seine nets, belonging to 78 species, 22 families and six orders. Characiformes was the most diverse taxonomic group in the samples, followed by Gymnotiformes and Siluriformes. Our findings indicate that the fish fauna of streams in the Madeira- Purus interfluvial plain is both rich and diverse and should be considered during the implementation of strengthened environmental conservation strategies in this region. © 2011 Check List and Authors

Home-range size of the bare-ear marmoset (Callithrix argentata) at Alter do Chao, Central Amazonia, Brazil

We studied factors affecting variation in home-range size of four groups of bare-ear marmosets (Callithrix argentata) in patches of forest within a central Amazonian savanna. We determined relative use of different parts of the home range by radiotelemetry. We estimated fruit availability monthly in transects through each home range and mapped the habitats within the home range of each group. We determined the densities of gum- and fruit-producing trees in 18 50 x 50-m quadrats and related these data to the frequency of use by marmosets. Home-range size varied by a factor of 6 between groups, even though the study area covered <15 km2 and included only one major biome. Marmoset activity was concentrated in areas with many gum-producing trees. Monthly range size is positively correlated with fruit availability only for the group with the largest home range; the other groups appeared to be responding to other factors. Home-range sizes appeared to be limited by the size of the main patch of contiguous forest available to each group. Our findings suggest that conservation planning that does not consider the possibility of large differences among primate home-range sizes may be unsatisfactory

Diversity and distribution of frogs in an Amazonian savanna in Brazil

We studied the distribution of anurans in savanna, regrowth and mature forest at the mouth of the Tapajos river in Brazilian Amazonia. We sampled 31 sites on the right bank of the Tapajos river and on the shores of lakes nearby, and recorded all acoustic and visual observations of frogs. We found 18 anuran species: Leptodactylidae (8), Hylidae (7), Bufonidae (2) and Pseudidae (1). The distribution of species indicated that some species are generalists and others are restricted to certain habitats. The species at Alter do Chao are a subset of those found in forested sites in Amazonia. Lakes and forested areas had the greatest anuran diversity, but are also the areas most disturbed by tourist development and agriculture. Reduction of anuran diversity in the area could be minimized by concentrating development along the main beaches of the Tapajos river