Abstract. In the Wet Chaco region of Argentina, increasing shrub encroachment in savannas over the last few decades has led to important changes in the structure and functioning of the landscape. Some sectors of this territory are characterized by the appearance of circular clusters of woody patches, dispersed throughout the grassland matrix. The increasing size of these patches leads to a gradual change from grassland to dense shrubland. We studied these circular woody patches in the eastern region of the Argentine province of Formosa and characterized the variation in terms of floristic composition, diversity and predominant seed dispersal mode in different size patches. We observed an increase in species richness, diversity and compositional heterogeneity among patches with increasing patch size. Seed dispersal by animals, especially birds, is an important factor in the expansion of these woody vegetation patches within the grassland matrix.

In the Wet Chaco region of Argentina, increasing shrub encroachment in savannas over the last few decades has led to important changes in the structure and functioning of the landscape. Some sectors of this territory are characterized by the appearance of circular clusters of woody patches, dispersed throughout the grassland matrix. The increasing size of these patches leads to a gradual change from grassland to dense shrubland. We studied these circular woody patches in the eastern region of the Argentine province of Formosa and characterized the variation in terms of floristic composition, diversity and predominant seed dispersal mode in different size patches. We observed an increase in species richness, diversity and compositional heterogeneity among patches with increasing patch size. Seed dispersal by animals, especially birds, is an important factor in the expansion of these woody vegetation patches within the grassland matrix.

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A B S T R A C TDifferent substrates of varying composition, color, texture and orientation may selectively influence recruitment of sessile invertebrates and thereby influence the resultant community. Thus substrates may act as a barrier to the establishment of non-indigenous species (NIS). In southern Brazil, granite is the main rock forming natural rocky walls that are available for encrusting organisms. In this study we tested whether granite selectively influences recruitment and impedes colonization by introduced and cryptogenic species that are already established on artificial substrates within the region. Plates of rough cut granite and of polyethylene were made available each month under a pier at a yacht club in Paranaguá Bay. A community is already established on concrete columns and fiber glass floats on the piers. After one, two and twelve months, the faunal composition of the plates was compared between the two treatments and other artificial substrates. Granite was recruited by all the seven introduced species found in the Bay and by 18 of 26 cryptogenic species and therefore is ineffective as a barrier to NIS colonization. R E S U M OSubstratos de diferentes materiais, cores, texturas e orientação podem influenciar seletivamente no recrutamento de invertebrados sésseis e, assim, influenciar a comunidade resultante. Deste modo, o substrato pode funcionar como barreira contra o estabelecimento de espécies não nativas (NIS, na sigla em inglês). No sul do Brasil, o granito é a principal rocha formadora de costões rochosos naturais disponíveis para organismos incrustantes. Nesta investigação, nós testamos se o granito seleciona o recrutamento de espécies e se poderia, assim, impedir a colonização de espécies introduzidas ou criptogênicas já estabelecidas em substratos artificiais na região. Placas não polidas de granito e de polietileno foram submersas a cada mês em um píer de um iate clube na Baía de Paranaguá. Há uma comunidade já estabelecida sobre colunas de concreto e sobre flutuadores de fibra de vidro presentes no iate clube. Depois de um, dois e doze meses, as espécies presentes nas placas de diferentes materiais foram comparadas entre si e também com outros substratos. O granito foi colonizado por todas as sete espécies introduzidas encontradas na região, e por 18 das 26 espécies criptogênicas, sendo então ineficaz como barreira contra a colonização de NIS.

The study of biological invasions can be roughly divided into three parts: detection, monitoring, mitigation. Here, our objectives were to describe the marine fauna of the area of the port of São Sebastião (on the northern coast of the state of São Paulo, in the São Sebastião Channel, SSC) to detect introduced species. Descriptions of the faunal community of the SSC with respect to native and allochthonous (invasive or potentially so) diversity are lacking for all invertebrate groups. Sampling was carried out by specialists within each taxonomic group, in December 2009, following the protocol of the Rapid Assessment Survey (RAS) in three areas with artificial structures as substrates. A total of 142 species were identified (61 native, 15 introduced, 62 cryptogenic, 4 not classified), of which 17 were Polychaeta (12, 1, 1, 3), 24 Ascidiacea (3, 6, 15, 0), 36 Bryozoa (17, 0, 18, 1), 27 Cnidaria (2, 1, 24, 0), 20 Crustacea (11, 4, 5, 0), 2 Entoprocta (native), 16 Mollusca (13, 3, 0, 0). Twelve species are new occurrences for the SSC. Among the introduced taxa, two are new for coastal Brazil. Estimates of introduced taxa are conservative as the results of molecular studies suggest that some species previously considered cryptogenic are indeed introduced. We emphasize that the large number of cryptogenic species illustrates the need for a long-term monitoring program, especially in areas most susceptible to bioinvasion. We conclude that rapid assessment studies, even in relatively wellknown regions, can be very useful for the detection of introduced species and we recommend that they be carried out on a larger scale in all ports with heavy ship traffic.