Environmental filters and biotic interactions drive species richness and composition in ecotone forests of the northern Brazilian Amazonia

The structure of tree communities in tropical forests depends on environmental filters and biotic interactions such as competition and facilitation. Many ecotone forests in Northern Amazonia are intriguingly populated by tree assemblages characterized by distinct abundances of a single species, Peltogyne gracilipes (Leguminosae). It is unclear whether this pattern solely reflects environmental filters or also antagonistic interactions among species with similar habitat requirements. The aim of this study was to determine the response of species richness and composition to environmental filters, and analyze the role of P. gracilipes in structuring tree communities in ecotone forest areas of the Northern Brazilian Amazonia. We sampled 129 permanent plots along a hydro-edaphic gradient. All arboreal individuals with stem diameter ≥10 cm were measured and identified. Multiple regressions were performed to test the effects of environmental filters, and abundance of P. gracilipes on the tree species richness and composition. Species richness and composition responded to the same filters which, in turn, affected species composition directly and indirectly, through the abundance of P. gracilipes. Our results indicate that both abiotic filters and biotic interactions shape the studied tree communities. P. gracilipes can be considered an indicator species of hydro-edaphic conditions, but also is itself a driver of tree community structure.

Adaptações estruturais e potencial plástico de Schinus terebinthifolia Raddi. (Anacardiaceae) em diferentes formações de restinga

Plantas da Restinga se desenvolvem sob condições ambientais heterogêneas, principalmente quando se distribuem ao longo de um gradiente. O presente estudo avaliou as adaptações morfoanatômicas foliares de Schinus terebinthifolia Raddi (Anacardiaceae) ocorrente em perfis fitofisionômicos de restinga: arbustiva, arbustivo-arbórea e floresta de transição. Em cada perfil fitofisionômico foram selecionados dez indivíduos dos quais foram coletadas quinze folhas totalmente expandidas para análise de atributos morfoanatômicos funcionais, tais como: massa fresca e seca, área foliar, área específica foliar, densidade foliar e estomática e espessura de tecidos. Variáveis ambientais como nutrição edáfica e radiação luminosa foram mensuradas. As populações foram comparadas por meio de ANOVA e PCA. Os atributos anatômicos mostraram-se menos plásticos que os morfológicos. As populações mostraram-se distintas entre si, sendo tipicamente xeromórfica na formação arbustiva e mesomórfica na fisionomia florestal, em função da oferta nutricional do solo, além da variância de temperatura e umidade. As diferenças encontradas são uma resposta aos fatores ambientais, principalmente ao gradiente edáfico que atua como um filtro ambiental que direcionada as adaptações estruturais da espécie. Structural adaptations and plastic potential of Schinus terebinthifolia Raddi. (Anacardiaceae) in different Restinga formations A B S T R A C TRestinga plants develop under heterogeneous environmental conditions, mainly when are distributed along a gradient. The present study evaluated the foliar morphoanatomy adaptations in Schinus terebinthifolia Raddi. (Anacardiaceae) occurring in three different formations of Restinga: shrubby restinga, shrubby and wooded restinga and transition forest. In each formation were selected ten individuals were selected from which 15 fully expanded leaves were collected for analysis of function morphoanatomic attributes. Environmental variables as edaphic nutrition and light radiation were measured. Populations had been compared by analysis of variance (ANOVA) and PCA. The anatomic attributes were less plastic than the morphologic. The populations were distinct from each other, being typically xeromorphic in the shrubby formation and mesomorphic in transition forest, as a function of a better or worse supply of soil nutrition. The differences found are an answer to the environmental factors, mainly the edaphic gradient which acts as an environmental filter that directs the structural adaptations of the species.Keywords: conservation of biodiversity, leaf morphoanatomy, edaphic gradient, phenotypic plasticity, oligotrophic scleromorphism.

Diferenciación florística en afloramientos calizos del sur de México y el centro de Brasil: un enfoque de diversidad beta

We studied the spatial arrangement of floristic diversity in two systems of limestone outcrops, located in two distant Neotropical sites: the region of Nizanda (S Mexico) and the Paranã Valley (Central Brazil). We addressed the question whether their vegetation could display a similar zonation, and we explored the relative effects of distance and an environmental gradient on α-, β- and γ-diversities. The limestone outcrops at both sites are similar in size and in elevation, but strongly differ in between-outcrop distance by an order of magnitude. At each study site three individual limestone outcrops were selected; in each of them three plant communities along the edaphic gradient were distinguished (a xerophytic scrub and two tropical dry forests types, one of which had a more xeric character than the other), and sampled for structural variables and floristic composition in 100-m2 plots. At both study sites, structural variables responded similarly to the edaphic gradient. Species density was larger in Nizanda for both α- and γ-diversity, but the largest value of β-diversity was obtained in Paranã. The edaphic gradient produced larger mean β-diversity values than the simple distance effect, with the interaction of both factors resulting in an even larger β-diversity. Classification analyses by site showed larger floristic similarities between the two xerophytic communities than those existing between them and the more mesic forests. The spatial arrangement of diversity showed that both α- and γ-diversity were smaller for the xerophytic communities. As hypothesized, the more extreme changes in community physiognomy were associated with larger β-diversity values