PERFIL DOS FRAGMENTOS DE MATA ATLÂNTICA COM REGISTROS DO MUTUM-DO-SUDESTE

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Abstract

RESUMO Avaliar os efeitos das mudanças no uso da terra sobre a biodiversidade se tornou uma questão-chave para conservação das espécies. Para isso, é necessário analisar a configuração e composição da paisagem em que determinada espécie ocorre. O objetivo foi traçar um perfil dos remanescentes florestais de Mata Atlântica localizados no sul da Bahia que apresentam registros atuais e históricos de Crax blumenbachii. Analisaram-se quatorze áreas utilizando diferentes escalas espaciais (escala de mancha, 500 m, 1 e 2 km) para calcular a quilometragem total e a distância mais próxima de estradas e rios até a borda da mancha, porcentagem de área ocupada por: floresta, floresta com cabrucas, pastagem e agricultura; densidade de fragmentos e a proximidade desses fragmentos até a borda de cada mancha, a área ocupada por casas e a distância dessas até a borda da mancha. Selecionou-se a escala de 2 km por melhor descrever a configuração e composição da paisagem. Há dois perfis de áreas com registros de mutum: (1) áreas com paisagens mais florestadas, com mais rios e estradas, pouca pastagem/agricultura e casas próximas, e (2) áreas distantes de casas, com estradas e fragmentos florestais próximos. Estas são caracteristicas de áreas com registros recentes ou históricos de mutum, e não necessariamente refletem qualidade de habitat para a espécie.

Translated abstract

ABSTRACT Assessing the effects of land use change on biodiversity has become a key issue for species conservation. Thus, it is necessary to analyze the configuration and composition of the landscape where a species occurs. The objective was to draw a profile of the forest remnants of the Atlantic Forest located in the south of Bahia state that present current and historical records of Crax blumenbachii. We analyzed fourteen areas using different spatial scales (patch scale, 500 m, 1 and 2 km) to calculate the total distance and distance from roads and rivers to the edge of the patch, percentage of area occupied by: forest, forest with cabrucas, cabrucas, pasture and agriculture; density of fragments and the proximity of these fragments to the edge of each patch, the area occupied by houses and their distance to the edge of the patch. We selected the 2 km scale to best describe the configuration and composition of the landscape. There are two profiles of areas with records of red-billed curassows: (1) areas with more forested landscapes, rivers and roads, low pasture/agriculture, and near human settlements, and (2) areas distant from houses, near roads and forest fragments. These features are related to areas with recent or historic records of red-billed curassows, and do not necessarily reflect habitat quality for the species.

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Beyond the Fragmentation Threshold Hypothesis: Regime Shifts in Biodiversity Across Fragmented Landscapes

Renata Pardini, Adriana de Arruda Bueno, Toby A. Gardner … (2010)

Ecological systems are vulnerable to irreversible change when key system properties are pushed over thresholds, resulting in the loss of resilience and the precipitation of a regime shift. Perhaps the most important of such properties in human-modified landscapes is the total amount of remnant native vegetation. In a seminal study Andrén proposed the existence of a fragmentation threshold in the total amount of remnant vegetation, below which landscape-scale connectivity is eroded and local species richness and abundance become dependent on patch size. Despite the fact that species patch-area effects have been a mainstay of conservation science there has yet to be a robust empirical evaluation of this hypothesis. Here we present and test a new conceptual model describing the mechanisms and consequences of biodiversity change in fragmented landscapes, identifying the fragmentation threshold as a first step in a positive feedback mechanism that has the capacity to impair ecological resilience, and drive a regime shift in biodiversity. The model considers that local extinction risk is defined by patch size, and immigration rates by landscape vegetation cover, and that the recovery from local species losses depends upon the landscape species pool. Using a unique dataset on the distribution of non-volant small mammals across replicate landscapes in the Atlantic forest of Brazil, we found strong evidence for our model predictions - that patch-area effects are evident only at intermediate levels of total forest cover, where landscape diversity is still high and opportunities for enhancing biodiversity through local management are greatest. Furthermore, high levels of forest loss can push native biota through an extinction filter, and result in the abrupt, landscape-wide loss of forest-specialist taxa, ecological resilience and management effectiveness. The proposed model links hitherto distinct theoretical approaches within a single framework, providing a powerful tool for analysing the potential effectiveness of management interventions.