Ronei Baldissera

Predação de sementes ao longo de uma borda de Floresta Ombrófila Mista e pastagem

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 Sao 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.

Metacommunity Composition of Web-Spiders in a Fragmented Neotropical Forest: Relative Importance of Environmental and Spatial Effects

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.

Effects of understory structure on the abundance, richness and diversity of Collembola (Arthropoda) in southern Brazil

The purpose of this study was to investigate the effects of different landscape structures on the understory Collembola community. Four different forest physiognomies were compared: Pinus spp. plantation, Eucalyptus spp. plantation, Araucaria angustifolia plantation, and a remaining native Araucaria forest. Three areas containing two sampling units (25 mx2 m each) were selected in each forest physiognomy. Understory Collembola collection was done with a 1x1 m canvas sheet held horizontally below the vegetation, which was beaten with a 1 m long stick, seasonally from September 2003 to August 2004. We evaluated the influence of forest physiognomies on the abundance, richness and diversity of Collembola communities. It was also verified if the habitat structure of each physiognomy was associated with the composition of the Collembola community. A total number of 4,111 individuals were collected belonging to the families Entomobrydae and Tomocerida (Entomobryomorpha), and Sminthuridae (Symphypleona), and divided in 12 morphospecies. Pinus plantation presented the highest richness, abundance and diversity of Collembola and it was associated to diverse understory vegetation. The abundance of Entomobrydae and Sminthuridae was associated to the presence of bushes, while Tomoceridae abundance was associated to the presence of trees. The habitat structure, measured through understory vegetation density and composition, plays an important role on the determination of the structure and composition of the Collembola community.

Assessment of the probability of colonization of local spider communities in an experimental landscape

Abstract Establishment of communities is a dynamic process initiated by immigration. Therefore, movements of individuals within a metacommunity are important for maintaining and increasing species distribution. We present results of a small landscape-level experiment that manipulated habitat size and diversity. We examined the rates of colonization of spider species, and the richness, abundance and composition of foliage-dwelling spiders. Estimation of colonization rates was based on maximum likelihood. The experimental landscape was composed of five blocks with four patches (two large, 1 m2; two small, 0.25 m2). Less diverse patches had seedlings of one plant species, whereas more diverse patches had four species with diverse structures. Eight periodic censuses of spiders arriving in the patches were performed (average interval between censuses, 28 days). The initial composition of colonizers was significantly different from the final composition, but rates of colonization did not differ between sizes and diversities, or their interaction. Abundances of spiders were positively influenced by patch size. Compositions in each temporal sample were determined by differences in the species pool migrating and arriving at an experimental landscape irrespective of habitat size or diversity. Larger patches were more likely to receive more colonists representing a wider array of species than small patches. The probability of colonization was independent of patch size and diversity, which contradicts theoretical predictions. The results highlight the high colonization capacity of spiders on spatial and temporal scales.

Distribution of Understorey Web Building Spiders Along an Interface Area of Araucaria Forest and Pinus Plantation in Southern Brazil

A floresta de Araucaria tem sido intensivamente impactada, o que possibilitou a criacao de mosaicos da paisagem com manchas da floresta original e outros usos da terra. A Floresta Nacional de Sao Francisco de Paula, RS, abriga um mosaico composto da floresta de Araucaria e plantacoes de Araucaria, Pinus e Eucalyptus. Este estudo visou avaliar a riqueza e abundância das assembleias de aranhas de teia de sub-bosque ao longo de uma area de contato entre uma mancha de Araucaria e outra de Pinus. Aranhas e outros artropodes foram coletados com guarda-chuva entomologico em cinco parcelas ao longo de cinco transectos paralelos a borda das manchas: uma na borda, duas outras a 10 m e a 30 m em cada mancha. Diferencas na riqueza e na abundância ao longo das distâncias foram analisadas por um teste de aleatorizacao. Foram realizadas regressoes lineares para avaliar a influencia da abundância de presas potenciais sobre a abundância e riqueza de aranhas de teia. Um total de 161 aranhas foi coletado (35 morfoespecies e 7 familias). Quatro morfoespecies representaram em torno de 42% da abundância. A familia mais rica foi Theridiidae (17 especies), seguida de Araneidae (11). A riqueza e a abundância de aranhas nao variaram entre as distâncias, mostrando que ha conectividade entre as vegetacoes dos sub-bosques. A abundância de presas potenciais influenciou positivamente a abundância e a riqueza de aranhas de teia. Presume-se que o manejo executado na reserva, com corte seletivo e longo tempo de rotacao, possibilite o crescimento do sub-bosque de Pinus, proporcionando recursos adequados para a manutencao da diversidade de aranhas. Palavras-chave: efeito de borda, ecotono, Mata Atlântica, manejo de florestas.

Diversity and composition of arbustive spiders in an Atlantic Forest fragment and two adjacent areas

O presente estudo investigou preliminarmente a diversidade e composicao de aranhas arbustivas em uma area de inicio de sucessao (arbustiva), uma area em estagio intermediario de sucessao (floresta secundaria) e um fragmento de Mata Atlântica em Torres, Rio Grande do Sul. Aranhas e outros artropodes (presas potenciais de aranhas) foram coletados com guarda-chuva entomologico, entre 50 e 200 cm de altura, em 10 parcelas em cada area no ano de 2008. A riqueza de especies foi acessada atraves de rarefacoes baseadas no numero de individuos, a composicao de especies foi analisada atraves de uma MANOVA por teste de aleatorizacao e a correlacao entre a composicao de especies de aranhas e as ordens de presas potenciais foi analisada atraves de um teste de Mantel. A abundância de aranhas nao variou entre as areas. A riqueza estimada foi maior no fragmento de Mata Atlântica, enquanto a composicao de aranhas foi diferente nas tres areas. Nao houve correlacao entre a composicao das assembleias de aranhas e a composicao de presas potenciais. A maior riqueza de aranhas arbustivas no fragmento de Mata Atlântica provavelmente se deve a presenca de uma comunidade vegetal mais diversa. As diferencas nas composicoes indicam que parte das especies desse fragmento podem nao ser capazes de utilizar ambientes da matriz, pois houve pouca sobreposicao de especies entre as areas com maior similaridade vegetal (madura e intermediaria). Os resultados indicam que as especies desse fragmento de Mata Atlântica sao seletivas no uso do habitat, mostrando a importância da protecao desse e de outros fragmentos para a conservacao das assembleias de aranhas arbustivas. Adicionalmente, areas em estagio intermediario de sucessao, contiguas a esse e outros fragmentos, podem ser importantes para algumas especies da floresta e tambem necessitam de atencao para sua conservacao. Palavras-chave: fragmentacao, especies matriz-tolerantes, sucessao florestal, estrutura de floresta.

Comparison between grassland communities with and without disturbances

Grassland management with fire and grazing is considered one of the main factors determining plant physiognomy and composition in grassland ecosystem. In that sense, it is thought that intermediate disturbances, neither high frequent and/or intense, nor absent, could enhance grasslands diversity by diminishing the competitive exclusion. Therefore, the present study evaluated the effect of disturbance exclusion over grassland plant communities in Plateau region of Southern Brazil. Two grasslands were sampled: one excluded of disturbances over the past 16 years, and other with fire and grazing disturbances. Six plots (1m2) were sorted inside each area. Inside each plot, plant species composition was described, while plant richness and evenness were assessed based on cover proportion of each species. The data analysis showed that the grassland without disturbances presented higher richness and evenness. Furthermore, there were differences in the species composition between the grasslands, with less tussock dominance in the disturbed grassland. In addition, plots’ compositions were more homogeneous in areas submitted to disturbances, despite of the high richness. It is concluded that dominant tussock grasses in the grassland without disturbances suppressed many forbs, leading to reducing the species richness and evenness. On the other hand, the presence of disturbances limits the tussocks growth allowing the development of other forbs species. Key words: grassland management, fire, cattle grazing, intermediate disturbance.