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This study investigates how abundance, diversity and composition of understorey spiders were influenced by four different forest habitats in a southern Brazilian Araucaria forest. The study area encompasses a landscape mosaic comprised of Araucaria forest, Araucaria plantation, Pinus plantation, and Eucalyptus plantation. Understorey spiders were collected by beating the vegetation inside three patches of each forest habitat. To assess possible predictors of spider assemblage structure, several patch features were analysed: potential prey abundances, estimation of vegetation cover, diversity index of vegetation types, patch ages, patch areas, and geographical distance between patches.To assess the influence of high-level taxa approaches on spider assemblage patterns, analyses were carried out individually for family, genera and species levels. Additionally, Mantel tests were carried out in underlying similarity matrices between each taxon. Significant differences in spider abundances among forest habitats were found. Pinus plantations showed the highest abundance of spiders and Eucalyptus plantations showed the lowest abundance. Spider abundance was significantly influenced by patch ages, geographical distance and vegetation cover. Expected numbers of families, genera and species did not vary among forest habitats. Spider composition of two Eucalyptus patches differed from the other forest patches, probably due to their low vegetation cover and isolation. Genera composition was the best correlate of species composition, showing that a higher-level surrogate can be an alternative to the species approach.The understorey spider diversity in this managed area could be maintained when suitable habitat structures are provided, thus ensuring the connectivity between different habitat types. Further studies should focus on individual species responses to the conversion of native forest to monocultures.

RESUMO -(Predação de sementes ao longo de uma borda de Floresta Ombrófila Mista e pastagem). Este estudo teve como objetivo avaliar o processo de predação de sementes em três árvores nativas (Mimosa scabrella Bentham, Prunus sellowii Koehne e Myrsine laetevirens Mez.) ao longo de uma borda de Floresta Ombrófila Mista e pastagem, na Floresta Nacional de São Francisco de Paula, RS, Brasil. Grupos de sementes foram distribuídos em dez pontos aleatórios nas distâncias: 0m, 25m, 50m, 100m e 250m da borda para dentro da floresta e 5m e 50m da borda para dentro da pastagem. As sementes foram monitoradas até a predação total ou até esgotado o tempo para germinação. Houve redução nas taxas de predação de sementes até 50m da borda para dentro da floresta em relação ao interior da floresta e da pastagem. M. scabrella e M. laetevirens apresentaram redução nas taxas de predação de sementes na pastagem próxima à borda da floresta. Os resultados indicam que houve decréscimo na atividade de predadores de sementes nas proximidades da borda florestal estudada, podendo ocorrer maior regeneração de plantas próximo à borda e um avanço da floresta na pastagem adjacente.Palavras-chave: predadores de sementes, efeito de borda, recrutamento de plântulas, floresta com Araucária ABSTRACT -(Seed predation along an edge gradient between Araucaria forest and pasture). This study aims to evaluate how seed predation of three native tree species (Mimosa scabrella Bentham, Prunus sellowii Koehne, and Myrsine laetevirens Mez.) could be altered along an edge between Araucaria forest and pasture at the National Forest of São Francisco de Paula, Rio Grande do Sul, Brazil. Groups of seeds were placed at ten random points in each of the following distances from the forest edge: 0m, 25m, 50m, 100m, and 250m from the edge into the forest, and 5m and 50m from the edge into the pasture. Seeds were monitored until total predation or until their time for germination was over. Seed predation rates decreased from the edge up to 50m inside the forest in relation to the forest interior and open pasture. M. scabrella and M. laetevirens showed a reduction in seed predation rates in pasture points that were located at the vicinities of the forest. The results indicated a decrease in the activity of seed predators near the forest edge, which could enhance plant community regeneration at the edge, and promote the expansion of the forest towards the adjacent pasture.

The distribution of beta diversity is shaped by factors linked to environmental and spatial control. The relative importance of both processes in structuring spider metacommunities has not yet been investigated in the Atlantic Forest. The variance explained by purely environmental, spatially structured environmental, and purely spatial components was compared for a metacommunity of web spiders. The study was carried out in 16 patches of Atlantic Forest in southern Brazil. Field work was done in one landscape mosaic representing a slight gradient of urbanization. Environmental variables encompassed plot- and patch-level measurements and a climatic matrix, while principal coordinates of neighbor matrices (PCNMs) acted as spatial variables. A forward selection procedure was carried out to select environmental and spatial variables influencing web-spider beta diversity. Variation partitioning was used to estimate the contribution of pure environmental and pure spatial effects and their shared influence on beta-diversity patterns, and to estimate the relative importance of selected environmental variables. Three environmental variables (bush density, land use in the surroundings of patches, and shape of patches) and two spatial variables were selected by forward selection procedures. Variation partitioning revealed that 15% of the variation of beta diversity was explained by a combination of environmental and PCNM variables. Most of this variation (12%) corresponded to pure environmental and spatially environmental structure. The data indicated that (1) spatial legacy was not important in explaining the web-spider beta diversity; (2) environmental predictors explained a significant portion of the variation in web-spider composition; (3) one-third of environmental variation was due to a spatial structure that jointly explains variation in species distributions. We were able to detect important factors related to matrix management influencing the web-spider beta-diversity patterns, which are probably linked to historical deforestation events.

O manejo do campo com pastejo e fogo é considerado um dos principais fatores determinantes da fi sionomia e composição de ecossistemas campestres. Nesse sentido, pode-se esperar que distúrbios intermediários, não frequentes e/ou intensos, nem ausentes, contribuam para aumentar a diversidade das comunidades campestres pelo relaxamento da exclusão competitiva. O presente estudo analisou o efeito da exclusão de distúrbios em campos do Planalto Sul Brasileiro, no Rio Grande do Sul. Dois campos foram amostrados: um excluído de distúrbios há 16 anos e outro com ocorrência de distúrbios (fogo e pastejo). Em cada área foram utilizadas seis parcelas de 1m2. Dentro de cada parcela foi analisada a composição, a riqueza e a equabilidade da vegetação com base em medidas de cobertura das espécies. A análise dos dados revelou que o campo com distúrbios apresentou maior riqueza e maior equabilidade. Verifi cou-se diferença na composição das espécies que ocorreram nos dois tipos de campo, com diminuição da dominância de plantas cespitosas no campo com distúrbios. Além disso, as parcelas foram mais homogêneas na área com distúrbios, mostrando baixa substituição das espécies, apesar de elevada riqueza. Conclui-se que a dominância de plantas cespitosas no campo excluído tende a suprimir outras plantas herbáceas, diminuindo a riqueza e a equabilidade. A presença de distúrbios, contudo, mantém as cespitosas com menor tamanho, o que propicia condições para o desenvolvimento de outras espécies herbáceas. Palavras-chave: manejo de campo, fogo, pastejo, distúrbio intermediário.

Habitat loss is one of the main consequences of landscape transformation by humans. Monitoring biodiversity changes in areas under different management strategies is fundamental for species conservation. Our study is the first to assess the role of forest disturbance history on spider (Araneae) biodiversity in the westernmost portion of the Atlantic Forest. We analyzed taxonomic and functional aspects of spider assemblages in understories in a large forest fragment in southwestern Brazil. Spiders were sampled in five 30 m × 5 m plots over three seasons in three areas with different management histories: clear-cutting, selective logging, or native plots. We also characterized tree basal area, tree density, and canopy openness. The clear-cut plots showed more canopy openness and low habitat heterogeneity due to the high density of one pioneer native tree species. Forest structure in selective logging and native plots was similar. Spider richness, abundance, and functional richness were affected only by the season. Species composition also differed among the areas depending on the season. The abundance of web-building species was mainly associated with clear-cut areas in winter and spring. These results highlight the importance of natural regeneration in the Atlantic Forest after disturbance for the conservation of regional spider biodiversity.

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