No abstract

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.

Esta pesquisa teve por objetivo avaliar a in uência da luminosidade e da dist ncia de igarap sobre a densidade de pl ntulas em oresta de terra rme na Amazônia Central. Foram instaladas vinte parcelas, onde medimos a porcentagem de abertura de dossel e a dist ncia do igarap , al m de contar o n mero de pl ntulas. Foi eita uma regressão linear da abertura de dossel com a densidade de pl ntulas e uma AN A da densidade de pl ntulas em un ão da dist ncia do igarap . Foi registrado um total de 229 indivíduos de pl ntulas densidade de pl ntulas 11 plantas m 2 . Dentre as variáveis ambientais a eridas, somente abertura de dossel in uenciou positivamente a densidade de pl ntulas. Uma pequena amplitude no aumento da luminosidade pode ocasionar um acr scimo na densidade de pl ntulas. A densidade de pl ntulas não di eriu em rela ão dist ncia do igarap , devido baixa competitividade e adapta es das esp cies que ocorrem em áreas alagadas. Palavras-chave: Dist ncia de igarapuminosidade Pl ntula n uence o environ ental variables on the density o shrub and tree seedlin s in an pland orest in the Central A a on is researc aimed to evaluate t e in uence o luminosit and distance rom an igarap on seedling densit in an upland orest in t e Central Amazon. ent plots ere installed, ere e measured t e percentage o canop openness, and t e distance rom an igarap , and e also counted t e number o seedlings.e obtained a linear regression o canop openness it t e seedling densit and an AN A o seedling densit according to t e distance rom an igarap . e registered a total o 229 seedling individuals seedling densit 11 plants m 2 . Among t e environmental variables measured, onl canop openness as positivel in uenced on Biotemas, 27 (3): 191-195, setembro de 2014 ISSNe 2175 http://dx

Epiphytes are common in the canopy of temperate and tropical forests, where they substantially contribute to species diversity and to key ecosystem processes. However, little is known about the effects caused by deforestation on this group of species, especially in northeastern Brazil, an area experiencing intense anthropogenic pressure. This study aimed to evaluate the effect of environmental variables on the structure of assemblies of vascular epiphytes in a fragment of open ombrophilous forest, Areia, northeastern Brazil. Sixty 10 × 10 m sampling plots were installed to cover different environments within the fragment. The relationship between environmental variables and species composition was evaluated by means of a generalized linear mixed model. The composition of assemblies of epiphytes differed with respect to distance from the edge and luminosity. In the study area, deforestation led to a change in the composition of epiphytic species both at the edge and the interior of the fragment.Edge eff ect on vascular epiphytic composition in a fragment of Atlantic Forest in northeastern Brazil Acta bot. bras. 29(2): 270-273. 2015.

Aim Distinguishing ecological and evolutionary processes that structure assemblages can provide a comprehensive vision of the variation in species turnover in heterogeneous regions. However, the causes of spatial variation in organism assemblies in most of the Amazon still require further studies. In view of this, our objective was to determine the relative roles of species interactions, categorical and continuous environmental filters and isolation by distance in the taxonomic and functional composition of lizard assemblages. Location Amazonian rainforest. Taxon Lacertilia. Methods We sampled 14 sites along 880 km in the Madeira‐Purus interfluvial region, central‐south‐western Amazonia. We used multiple linear models applied to distance matrices, spatial correlograms and partitioned variance to distinguish the effects of geographical distances from environmental distances on lizard assemblages. Additionally, to better understand the effects of environmental gradients and forest type on species traits, we used a combination of RLQ and fourth‐corner analysis. Results Variance in taxonomic distance was mainly explained by a continuous environmental gradient that selects different species. Although we found no evidence of overdispersion or clustering of traits, functional distance was mainly explained by forest type and precipitation. The weak effect of geographical distance on lizard assemblages suggests that different environmental conditions have selected distinct subsets of species and functional traits. Main Conclusions We showed that the structural heterogeneity along an environmental gradient in Amazonia has a significant impact on the taxonomic and functional composition of lizard assemblages. Environmental filtering along the interfluvial region has caused species turnover and determined differences in the functional characteristics found between assemblages in dense and open forests. These results are relevant for conservation since local species or trait subsets change across the landscape and are therefore irreplaceable in the case of local extinction.