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.

Although both niche‐based and neutral processes are involved in community assembly, most models on the effects of habitat loss are stochastic, assuming neutral communities mainly affected by ecological drift and random extinction. Given that habitat loss is considered the most important driver of the current biodiversity crisis, unraveling the processes underlying the effects of habitat loss is critical from both a theoretical and an applied perspective. Here we unveil the importance of niche‐based and neutral processes to species extinction and community assembly across a gradient of habitat loss, challenging the predictions of neutral models. We draw on a large dataset containing the distribution of 3653 individuals of 42 species, representing 35% of the small mammal species of the Atlantic Forest hotspot, obtained in 68 sites across three continuously‐forested landscapes and three adjacent 10 000‐ha fragmented landscapes differing in the amount of remaining forest (50%, 30% and 10%). By applying a null‐model approach, we investigated β‐diversity patterns by detecting deviations of observed community similarity from the similarity between randomly assembled communities. Species extinction following habitat loss was decidedly non‐random, in contrast to the notion that fragmented communities are mainly driven by ecological drift. Instead, habitat loss led to a strong biotic homogenization. Moreover, species composition changed abruptly at the same level of landscape‐scale habitat loss that has already been associated with a drastic decline in species richness. Habitat loss, as other anthropogenic disturbances, can thus be seen as a strong ecological filter that increases (rather than decreases) the importance of deterministic processes in community assembly. As such, critical advances for the development of conservation science lie on the incorporation of the relevant niche traits associated with extinction proneness into models of habitat loss. The results also underscore the fundamental importance of pro‐active measures to prevent human‐modified landscapes surpassing critical ecological thresholds.

-The feeding ecology of the maned wolf (Chrysocyon brachyurus) was studied from 1998 to 2002 in the Ecological Station of Itirapina, São Paulo State, southeastern Brazil, including estimates of prey number and biomass consumption. A total of 325 faecal samples was collected in the area. The species is omnivorous, with a broad diet including 68 species or morphospecies of fruits and animals. Armadillos (Dasypodidae), wolf's fruit (Solanum lycocarpum) and small mammals (mostly Clyomys bishopi) were the bulk of the diet, comprising 72.8 % of the total estimated biomass consumed (185,323.4 g). In terms of frequency of occurrence, on the other hand, only small mammals and other miscellaneous fruits yielded 43.4 % of the total occurrences (N = 1,054). Animal prey ranging from 0.01 and 0.1 Kg were the most captured category, resulting in 44.2 % of 507 captured animals. The maned wolf seems to be seasonally opportunistic, at least for fruits and insects, as indicated by the variation of the consumption of these items along the year. The higher consumption of fruits and animals characteristic of savannah can be an important factor to consider in future management plans for the species.Key words: Chrysocyon brachyurus, maned wolf, savannah, grassland, feeding ecology, diet, Brazil.Resumo -A dieta do lobo-guará (Chrysocyon brachyurus) foi estudada entre 1998 e 2002 na Estação Ecológica de Itirapina, Estado de São Paulo, incluindo estimativas de número de presas e biomassa ingerida. Um total de 325 amostras fecais foi coletado na área de estudo. A espécie pode ser considerada onívora, com uma dieta variada incluindo 68 espécies ou morfo-espécies de frutos e animais. Os tatus (Dasypodidae), fruta-de-lobo (Solanum lycocarpum) e pequenos mamíferos (principalmente Clyomys bishopi) constituíram a base da dieta, com 72,8% do total de biomassa consumida (185.323,4 g). Por outro lado, em termos de freqüência de ocorrência, apenas os pequenos mamíferos e outros frutos compreenderam 43,4% do total de ocorrências (N = 1.054). Presas animais entre 0,01 e 0,1 Kg foram as mais consumidas, representando 44,2 % do total de 507 indivíduos capturados. O lobo-guará apresenta oportunismo sazonal pelo menos para frutos e insetos, a julgar pela variação no consumo desses itens nas diferentes estações do ano. O alto consumo de frutos e animais provenientes do cerrado deve ser levado em conta em planos futuros de manejo da espécie. Palavras-chave:Chrysocyon brachyurus, lobo-guará, cerrado, campo, ecologia alimentar, dieta, Brasil.

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Avaliação e ações prioritárias para a conservação da biodiversidade da Mata Atlântica e Campos Sulinos. MMA/SBF. Brasília. 40p.