RESUMO -A criação de unidades de conservação nem sempre é determinada por critérios técnicos e/ou socioambientais, comprometendo, assim, sua efetividade na proteção da biodiversidade local. Este estudo analisou a potencialidade do Monumento Natural Grota do Angico, localizado no Alto Sertão do Estado de Sergipe, em relação aos aspectos de paisagem, além de analisar possíveis ameaças, de forma a subsidiar estratégias de conservação para a manutenção da biodiversidade local. Para o estudo foi adaptado um protocolo de avaliação de fragmentos prioritários para a conservação do Cerrado. Os indicadores foram obtidos a partir de estudos feitos no local e de um levantamento das espécies vegetais exóticas invasoras, realizado em uma área de 251 ha, sendo adicionalmente calculado o índice de circularidade para o Monumento. Os valores obtidos pelo protocolo foram considerados típicos de áreas com baixos riscos à conservação. As características do MONA Grota do Angico são pouco satisfatórias para manutenção da diversidade de espécies, apresentando área total pequena em relação a outras áreas, formato alongado e índice de circularidade de apenas 0,17 (de uma escala de 0 a 1). Entretanto, a reserva protege a calha do Baixo São Francisco e na região há mais duas unidades de conservação que fazem parte de um corredor ecológico. As ameaças encontradas, como queimadas, desmatamento, espécies exóticas invasoras e gado, requerem monitoramento. Conclui-se que, de forma geral, o MONA Grota do Angico possui condições de abrigar uma biodiversidade considerável, desde que as ameaças sejam monitoradas e geridas.Palavras-chave: Áreas protegidas; Impactos antrópicos; Planejamento. ASPECTS OF LANDSCAPE ECOLOGY AND THREATS TO BIODIVERSITY IN
Fire and herbivory are known to modify plant community structure. Many studies have suggested that fire ashes may increase soil nutrients in dystrophic soils. Herbivores may also change plant community structure through direct effects of herbivory and affecting nutrient cycling. Leaf-cutting ants were traditionally viewed as herbivores, although their role may be more complex, because their nests affect both chemical and physical soil properties, thus affecting plants indirectly. We investigated the effects of frequent burning and of leaf-cutting ants on the nutrient status of an herbaceous and a shrub species occurring in the Brazilian Cerrado, a habitat that is characterized by natural burnings. The proximity of ant nests resulted in an increase of nutrients in the leaves of both vegetation strata, whereas burning sometimes resulted in a decrease of nutrients. Our results do not lead to a possible positive effect of fire on plant nutrient content. On the other hand, ant nests may represent an important source of nutrients for plants on the nutrient-depleted Cerrado soils and may accelerate vegetation recovery after burning.
Several species of arthropods inhabiting forest fragments interact with managed areas. The importance of such areas to biodiversity conservation, however, is not well established. Communities of solitary wasps and bees (Insecta: Hymenoptera) play a key role in agroecosystem functioning and they have been used in studies of biodiversity assessment in different land-use types. We aimed to assess patterns of species richness and composition of solitary wasps and bees over a 1-yr period in a gradient of decreasing land-use intensity formed by pastures, alley croppings, young fallows, and old fallows using trap nests. Old fallows had the highest species richness of wasps and bees, harboring all bee species and 86 percent of wasp species occurring in the region, while the remaining land-uses had similar species richness. Vegetation structure (tree richness) and relative humidity explained most of the variance for the species richness of wasps. For bees, however, there was no influence of environmental factors on the community among land-use types, indicating better adaptability of this group to environmental variations related to land-use. The composition of solitary wasp communities (but not those of bees) differed among land-use types, and the occurrence of rare species in most cases was restricted to old fallow sites. In conclusion, the community of solitary wasps and bees is contingent on land-use, with solitary wasps more sensitive to anthropized areas. For both groups, less anthropized areas harbor a greater richness and number of rare species while more intensively managed land-use types harbor higher abundances.Abstract in Portuguese is available in the online version of this article.
-Edge effects are considered a key factor in regulating the structure of plant communities in different ecosystems. However, regardless to few studies, edge influence does not seem to be decisive in semiarid regions such as the Brazilian tropical dry forest known as Caatinga but this issue remains inconclusive. The present study tests the null hypothesis that the plant community of shrubs and trees does not change in its structure due to edge effects. Twenty-four plots (20 x 20 m) were set up in a fragment of Caatinga, in which 12 plots were in the forest edges and 12 plots were inside the fragment. Tree richness, abundance and species composition did not differ between edge and interior plots. The results of this study are in agreement with the pattern previously found for semiarid environments and contrasts with previous results obtained in different environments such as Rainforests, Savanna and Forest of Araucaria, which indicate abrupt differences between the border and interior of the plant communities in these ecosystems, and suggest that the community of woody plants of the Caatinga is not ecologically affected by the presence of edges.
Ecological succession is a complex processes involving changes in the structure of plant community and it is an important factor determining the structure of arboreal ants assemblages, but little is known about the effects of succession on ant assemblages in regions of Tropical Dry Forests (TDFs), such as the Brazilian Caatinga. The aim of this study was to investigate the effects of ecological succession on the richness and species composition of arboreal ants in fragments of Caatinga, testing the following hypothesis: i) the richness of arboreal ants increases along a gradient of forest succession, in response to tree richness and/or density; ii) species composition of arboreal ants differs among stages of forest succession due to differences in vegetation structure in theses stages. This study was conducted in 15 plots distributed in three areas with different stages of secondary succession (early, intermediate and late). Tree density and richness were used as surrogate of vegetation structure. Ants were sampled using the technique of beating the foliage and baited pitfall traps, where five trees were sampled per plot, totaling 75 individual trees sampled. We sampled 37 species of ants, distributed in 16 genera and five subfamilies. Ant richness differed among stages of succession and seasons, with higher number of species in the late succession and rainy period, also increasing with tree richness and density. Besides, there was a distinct composition of ant species among stages of succession and seasons. Results obtained in this study reinforce the importance of using ants as environmental bioindicators, since the sensitivity to environmental variations of this group enables us to differentiate early and late successional stages of forest succession in Caatinga environment.
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