No abstract

Riparian habitats are important for the maintenance of regional biodiversity. Many studies have compared bird distributions between riparian and non-riparian habitats but have not established how wide riparian habitats used by birds are, as measured by distance from the nearest stream. We investigated the distribution of understory birds along gradients of distance from streams, soil clay content, and slope in a central Amazonian forest, by mist-netting birds three times in 45 plots. We used nonmetric multidimensional scaling (NMDS) to reduce the dimensionality of species quantitative (abundance) and qualitative (presence-absence) composition to one multivariate axis. Estimates of the width of riparian habitats as indicated by understory birds depended on the community attribute considered, measuring 90 m for species quantitative composition and 140 m for species qualitative composition. Species distributions were correlated with clay content but were independent of slope, while distance from streams was positively correlated with clay content but independent of slope. Clay content affects plant species composition, which in turn, may influence bird species composition. However, distribution patterns of birds in relation to distance from streams are consistent among studies carried out in many different temperate and tropical regions, indicating an effect of distance from streams itself. Protection of riparian habitats is one of the most widely used conservation strategies, and Brazilian environmental legislation mandates the protection of a 30 m wide strip of riparian vegetation on either side of small streams. We show that the protected strip should be much wider and recommend strategies to place other forms of land protection contiguous with riparian areas so that Brazilian environmental legislation better fulfills its role of protecting biodiversity associated with riparian habitats.

Tropical forest mammal assemblages are widely affected by the twin effects of habitat loss and habitat fragmentation. We evaluated the effects of forest patch metrics, habitat structure, age of patch isolation, and landscape metrics on the species richness, abundance and composition of small mammals at 23 forest fragments (ranging in size from 43 to 7,035 ha) in a highly deforested 3,609-km2 landscape of southwestern Brazilian Amazonia. Using pitfall traps and both terrestrial and arboreal traplines of Sherman, Tomahawk and snap traps, we captured a total of 844 individuals over 34,900 trap-nights representing 26 species and 20 genera of small-mammals, including 13 rodent and 13 marsupial species. We also consider the effects of distance from forest edges on species occupancy and abundance. Overall small mammal abundance, species richness and species composition were primarily affected by the quality of the open-habitat matrix of cattle pastures, rather than by patch metrics such as fragment size. Ultimately, small mammal community structure was determined by a combination of both landscape- and patch-scale variables. Knowledge of the anthropogenic factors that govern small mammal community structure is of critical importance for managing the persistence of forest vertebrates in increasingly fragmented neotropical forest landscapes

We investigated the variation of stable (6'3C) soil carbon isotopes in relation to depth in seven of the most important savanna areas to adjacent contiguous forests in the Amazon region. The 6I3C of bulk organic matter in all profiles from forested sites increased with soil depth. In forest profiles from Amapb, Alter do Chso, and Roraima, the enrichment was less than 3.5' 360 between deeper soil and surface layers, suggesting that C3 plants have remained the dominant vegetation cover. On the other hand, in forest soil profiles from Humaitb and Carolina sites, the 6'3C enrichment was greater than 3.5%0, indicating the influence of past C4 vegetation or a mixture of C3/C4 vegetation (woody savanna). The surface 6I3C values in the savanna profiles were 5-13Yw greater than the comparable forest profiles, indicating the influence of C4 vegetation. Two kinds of isotopic distribution were observed in deeper layers. The savanna profiles at Alter do Chso, Chapada dos Parecis, and Redengo had relatively constant 6I3C values throughout the profile, suggesting minor past changes in the vegetation composition. In profiles at Amapb, Roraima, Humaitb, and Carolina, 6% values decreased with depth from the surface and converged with comparable forest values, suggesting more woody savanna in the past than exists currently. RESUMON6s investigamos neste estudo a variago em profundidade dos isbtopos estbveis de carbon0 (6I3C) da matkria orginica do solo (SOM) em sete hreas de savanas e florestas da regiSo Amazhica. 0 s valores de 6I3C da SOM aumentaram corn a profundidade do solo. Nos perfis em floresta do Amapb, Alter do Chso e Roraima o enriquecimento isotbpico com a profundidade foi menor que 3,5%0, sugerindo que plantas do tip0 C3 foram sempre o tip0 de vegetago dominante. Por outro lado, nos perfis em floresta de Humaid e Carolina, o enriquecimento isotbpico foi maior que 3,5%0, indicando a influencia no passado de uma vegetago do tip0 C4, ou uma mistura de vegetago C3/C4 (savana lenhosa). 0 s valores de 6% na superficie do solo em savanas foram cerca de 5 a 13Yw maiores que 0 s perfis em floresta, evidenciando a influencia da vegetago C,. Dois tipos de disuibuiqio isotbpica foram observados em camadas mais profundas. Nas savanas de Alter do Ch5o, Chapada dos Parecis e Redengo 0 s valores 6I3C foram constantes ao longo do perfil do solo, sugerindo que r6o houveram mudanps sigdicativas na vegetago. Nos perfis do Amapb, Roraima, Humaid e Carolina, 0 s valores de 6I3C diminuiram corn a profundidade do solo, aproximando-se aos Vaores encontrados na floresta, sugerindo a existencia no passado de uma savana mais lenhosa que a actual.K?y word: Amazon; Brazil; carbon uotope; radiocarbon; savanna; tropical firest; vegetation change.

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This study describes changes in the numbers of plant species fruiting during six years in I ha of Amazonian savanna on the right bank of the Tapajós River, Brazil. The work was based on fleshy fruits from tree and shrub-layer species eaten by birds. The area was burned in the first two years, protected during the following two years and burned again in the last two years. The number of tree species fruiting did not differ significantly between years with and without fire. The number of shrub-layer species fruiting was markedly reduced in years with fire, but the responses varied between species. Data on changes in shrub cover after two consecutive years of fire indicate that species also respond differently in terms of biomass lost due to fires. The two most abundant genera of shrubs, Miconia and Myrcia, had their cover reduced by up to 95% and 72% respectively. The area made available by the loss of shrubs was occupied mainly by the grass Paspalum carinatum. The fires and the decrease in the availability of fruits occurred during the season in which most species of birds breed. An interval of less than three years between fires is insufficient for shrub-layer species to recover.

We studied the energy flow from C and C plants to higher trophic levels in a central Amazonian savanna by comparing the carbon stable-isotope ratios of potential food plants to the isotope ratios of species of different consumer groups. All C plants encountered in our study area were grasses and all C plants were bushes, shrubs or vines. Differences in δC ratios among bushes (x¯ = -30.8, SD = 1.2), vines (x¯ = -30.7, SD = 0.46) and trees (x¯ = -29.7, SD = 1.5) were small. However the mean δC ratio of dicotyledonous plants (x¯ = -30.4, SD = 1.3) was much more negative than that of the most common grasses (x¯ = -13.4, SD = 0.27). The insect primary consumers had δC ratios which ranged from a mean of -29.5 (SD = 0.47) for the grasshopper Tropidacris collaris to a mean of -14.7 (SD = 0.56) for a termite (Nasutitermes sp.), a range similar to that of the vegetation. However, the common insectivorous and omnivorous vertebrates had intermediate values for δC, indicating that carbon from different autotrophic sources mixes rapidly as it moves up the food chain. Despite this mixing, the frogs and lizards generally had higher values of δC (x¯ = -21.7, SD = 1.6; x¯ = -21.9, SD = 1.8, respectively) than the birds (x¯ = -24.8, SD = 1.8) and the only species of mammal resident in the savanna (x¯ = -25.4), indicating that they are generally more dependent on, or more able to utilise, food chains based on C grasses.

Bolomys lasiurus is the only species of rodent commonly found in the savanna of Alter do Chão, central Amazonia. Peak densities during 42 months were less than have been reported from the cerrado biome of central Brazil. However, the population at Alter do Chão appears to be more stable than those in other areas and we never recorded zero densities. Many animals were captured over periods greater than 7 months, indicating that either mortality or dispersal was less than in previous studies. Mean home-range size of females was inversely related to the proportion of females that were gravid or lactating. Female home ranges were mutually exclusive and averaged 35% (SD = 8.2%) of male home ranges. Male home ranges overlapped extensively. Indices of home-range size varied seasonally and among years.