Our study aimed to understand the function(s) of roars of southern brown howler monkeys (Alouatta guariba clamitans). The study group called almost exclusively on its range borders and preferentially on early mornings, but with no dawn peak. Intergroup encounters were associated with 88% of all sessions. Predation deterrence and regulation of access to mating partners do not seem compatible with our findings, but more work is needed to reject the latter hypothesis. Their roars seem to be related to intergroup spacing, but through an active defence of borders, instead of mutual avoidance or regular advertisement of occupancy, as proposed for other howler monkey species.

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In this study we propose a model that represents the importance of large arborescent palms in the dynamics of seasonally-dry Amazonian forests. Specifically, the model is aimed at guiding the investigation of the role of large arborescent palms on forest regeneration and succession. Following disturbance, the high level of luminosity reaching recently formed forest gaps favors the quick proliferation of shade-intolerant lianas that, by casting shade on the crowns of mature forest trees and increasing tree-fall probability, suppress forest succession. Due to their columnar architecture palm trees are, however, not severely affected by vines. As the palms grow, the canopy at the gaps becomes gradually higher and denser, progressively obstructing the passage of light, thus hindering the growth of shade-intolerant lianas and enabling late-successional tree development and forest regeneration. Owing to the long time associated with forest regeneration, the model cannot be tested directly, but aspects of it were examined with field data collected at an Attalea maripa-rich secondary forest patch within a matrix of well-preserved seasonally-dry forest in the Southeastern Amazon. The results indicate that (1) forest disturbance is important for the recruitment of large arborescent palms species, (2) these palms can grow rapidly after an event of disturbance, restoring forest canopy height and density, and (3) secondary forest dominated by palm trees species may be floristically similar to nearby undisturbed forests, supporting the hypothesis that the former has undergone regeneration, as purported in the model. Key words: Amazon, Attalea maripa, forest dynamics, palm trees, regeneration. ResumoNeste estudo propomos um modelo que representa a importância de palmeiras arborescentes de grande porte na dinâmica das florestas amazônicas sazonalmente secas. Especificamente, o modelo visa guiar a investigação do papel destas palmeiras na regeneração da floresta. Após um evento de perturbação, a alta luminosidade das clareiras recentes favorece a rápida proliferação de lianas dependentes de insolação que, sombreando as copas das árvores e aumentando sua probabilidade de queda, tendem a interromper o processo de sucessão. Devido a sua arquitetura colunar, as palmeiras arborescentes, no entanto, não são severamente afetadas por lianas. À medida que estas palmeiras crescem, o dossel das clareiras se torna gradualmente mais alto e denso, limitando desta forma o crescimento das lianas e permitindo o desenvolvimento das árvores de estádios sucessionais tardios e, consequentemente, a regeneração da floresta. Devido ao longo período associado à regeneração da floresta o modelo não pode ser testado diretamente, mas aspectos deste foram examinados com dados de campo coletados em uma mancha de floresta secundária rica em Attalea maripa em uma matriz de florestas primárias bem preservadas no sudeste da Amazônia. Os resultados revelam que (1) eventos de perturbação florestal são importantes para o recrutamento das palmeiras arboresce...

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