ABSTRACT The island rule suggests that, when mainland animals are isolated on islands, large animals tend to become smaller, while small animals tend to become larger. A small frog in eastern Brazil, Phyllodytes luteolus (Wied-Neuwied, 1824), is widely distributed in association with bromeliads. At the end of the last glaciation, parts of the mainland became islands due to rising sea levels, thereby isolating frog populations on these islands. If the island rule holds, we predicted that frogs on islands would tend to be larger than frogs on the mainland. We compared sizes (weight and length) of 30 randomly selected male frogs from the mainland with 30 from an island in the state of Espírito Santo, Brazil. We also sampled population density on the island and mainland because concurrent with changing sizes, depending on the causal relationship, density may also change. As predicted, island frogs tended to be larger (both in snout-vent length and weight) and were much more abundant. While not specifically addressed in this study, the absence of predators and interspecific competitors may explain both of these trends.

Populations of Asterina stellifera Möbius, 1859 are declining in southern Brazil and today the species is on the Brazilian list of endangered species. Here we experimentally investigate the ecological role played by A. stellifera as a predator on the rocky substrate community by increasing densities of this species. Starfish taken from other, nearby, locations were added to three replicate plots and their density was maintained every 15 days. None of the total of 32 species that were identified in the encrusting community appeared to be influenced by the experiment. Two species, the barnacle Chthamalus bisinuatus Pilsbry, 1916 and the algae Gracilaria verrucosa (Hudson), showed small apparent responses to predation. We found that A. stellifera only exerts weak predation pressure on the community, even at high densities. This result is strikingly different from that observed for similar species in the northern hemisphere and in Australia.

Reprodução sexuada e assexuada, mortalidade e a dinâmica de fusões e fissões de colônias de Didemnum rodriguesi Rocha & Monniot, 1993 foram investigados e comparados no sul do Brasil, no inverno e verão. Tais eventos foram analisados por fotografias de áreas permanentemente demarcadas e coletas mensais de colônias. Os resultados indicam que esta espécie alterna sazonalmente a reprodução sexuada (verão) e assexuada (inverno). Durante o verão as colônias são mais abundantes e menores, com ovos e larvas incubados e taxas de recrutamento maiores. No inverno há um menor número de colônias, porém de maior tamanho e inférteis. Existe uma relação entre fecundidade e tamanho da colônia. Não foram encontradas diferenças estatísticas no número de eventos de fragmentação e fusão entre o verão e inverno, bem como para mortalidade. Conclui-se que esta espécie tem um ciclo de vida típico de espécies de maiores latitudes, com tempo limitado para a reprodução sexuada e alternância no investimento entre reprodução sexuada e assexuada.

Sexual and asexual reproduction and associated population dynamics were investigated in the colonial ascidian Didemnum rodriguesi Rocha & Monniot, 1993 (Didemnidae) in southern Brazil. Investment in sexual (production of new individuals) and asexual (colony growth) reproduction was compared between seasons. Permanently marked quadrats were repeatedly photographed to measure changes in colonies. Eggs and larvae were counted monthly in collected colonies. This species alternates seasonally between sexual (summer) and asexual (winter) reproduction. In summer, colonies were smaller, brooded eggs and larvae and recruitment rates were greater, while in winter, colony size was larger and eggs and larvae were absent. There is a relationship between fecundity and colony area. Fragmentation and fusion of colonies were similar in summer and winter, as well as mortality. In conclusion, D. rodriguesi has a lifecycle usual for high latitude ascidians with a limited time length for sexual reproduction and alternate investment in sexual and asexual reproduction along the year.

Senna multijuga (Rich.) H. S. Irwin & Barneby (Caesalpinaceae) é uma planta ornamental comum no sudeste do Brasil, suscetível ao dano por bruquíneos predadores de sementes. Com o objetivo de identificar os predadores de suas sementes e determinar seus ciclos populacionais, frutos de cinco árvores foram coletados em 2000 e 2001 e acondicionados em casa de vegetação até a emergência de adultos. Os bruquíneos foram identificados como Sennius crudelis Ribeiro-Costa & Reynaud, 1998, S. puncticollis (Fåhraeus, 1839) e S. nappi Ribeiro-Costa & Reynaud, 1998. Sennius crudelis foi a espécie mais abundante em 2000, seguida por S. puncticollis e S. nappi. Em 2001, Sennius crudelis foi seguida por S. nappi e S. puncticollis. Diferenças foram observadas entre as árvores com relação ao período de frutificação, refletindo na oviposição. O período de emergência dos adultos se inicia em julho tanto em casa de vegetação quan-to no campo. Os resultados demonstraram que as dinâmicas populacionais dos bruquíneos são complexas e a compreensão desses processos contribui para responder a muitas outras questões ecológicas do grupo.

Senna multijuga (Rich.) H. S. Irwin & Barneby (Caesalpinaceae) is a native ornamental tree common in southeastern Brazil and susceptible to seed damage due to bruchines. To identify seed predators and determine their population cycles, fruits from five trees were collected in 2000 and 2001 and stored in a green house until adult emerged. Seed beetles were then identified as Sennius crudelis Ribeiro-Costa & Reynaud, 1998, S. puncticollis (Fåhraeus, 1839) and S. nappi Ribeiro-Costa & Reynaud, 1998. Sennius crudelis was the most abundant species in 2000 followed by S. puncticollis and S. nappi. In 2001, Sennius crudelis was followed by S. nappi and S. puncticollis. Differences were observed among trees relating to fruiting period which reflected in the oviposition. Adult emergence begins in July in the green house and in the field. These results show that bruchine beetles have complex population dynamics, and understanding those dynamics is important to answer other ecological questions of the group.