NEW METHODS FOR THE STUDY OF VERTICAL STRATIFICATION OF NEOTROPICAL OPOSSUMS.

Novos métodos vêm sendo desenvolvidos para o estudo da estratificação vertical dos pequenos mamíferos neotropicais, como alternativas aos métodos convencionais que usam armadilhas de captura de animais vivos. Nesta revisão descrevemos três métodos alternativos para estudar a estratificação vertical dos marsupiais didelfídeos nas florestas tropicais: testes de desempenho em uma abordagem ecomorfológica, carretel de rastreamento e ninhos artificiais. O histórico de uso de cada um é revisto, discutindo suas vantagens e desvantagens, e apresentando exemplos de resultados inéditos obtidos através de seu uso. Testes de hipóteses mais acurados sobre estruturação de comunidades locais e questões relacionadas à demografia de populações podem ser obtidos com a combinação destes novos métodos com métodos convencionais, que se complementem, minimizando suas deficiências.New methods have been developed for the study of vertical stratification on small neotropical mammals, alternative to traditional methods using live traps. We reviewed three such alternative methods to study vertical stratification of didelphid marsupials in tropical forests: performance tests in an ecomorphological approach, spool-and-line, and artificial nests. The history of each method was reviewed, discussing their advantages and pitfalls, and presenting examples of the unique results reac,hed. More accurate tests of hypothesis about assemblage structure and population demography can be obtained by combination of traditional and alternative methods, which complement each other, minimizing their limitations

Small mammal responses to Amazonian forest islands are modulated by their forest dependence

Hydroelectric dams have induced widespread loss, fragmentation and degradation of terrestrial habitats in lowland tropical forests. Yet their ecological impacts have been widely neglected, particularly in developing countries, which are currently earmarked for exponential hydropower development. Here we assess small mammal assemblage responses to Amazonian forest habitat insularization induced by the 28-year-old Balbina Hydroelectric Dam. We sampled small mammals on 25 forest islands (0.83–1466 ha) and four continuous forest sites in the mainland to assess the overall community structure and species-specific responses to forest insularization. We classified all species according to their degree of forest-dependency using a multi-scale approach, considering landscape, patch and local habitat characteristics. Based on 65,520 trap-nights, we recorded 884 individuals of at least 22 small mammal species. Species richness was best predicted by island area and isolation, with small islands ( 200 ha; 10.8 ± 1.3 species) and continuous forest sites (∞ ha; 12.5 ± 2.5 species) exhibited similarly high species richness. Forest-dependent species showed higher local extinction rates and were often either absent or persisted at low abundances on small islands, where non-forest-dependent species became hyper-abundant. Species capacity to use non-forest habitat matrices appears to dictate small mammal success in small isolated islands. We suggest that ecosystem functioning may be highly disrupted on small islands, which account for 62.7% of all 3546 islands in the Balbina Reservoir

Indirect effects of habitat loss via habitat fragmentation: A cross-taxa analysis of forest-dependent species

Recent studies suggest that habitat amount is the main determinant of species richness, whereas habitat fragmentation has weak and mostly positive effects. Here, we challenge these ideas using a multi-taxa database including 2230 estimates of forest-dependent species richness from 1097 sampling sites across the Brazilian Atlantic Forest biodiversity hotspot. We used a structural equation modeling approach, accounting not only for direct effects of habitat loss, but also for its indirect effects (via habitat fragmentation), on the richness of forest-dependent species. We reveal that in addition to the effects of habitat loss, habitat fragmentation has negative impacts on animal species richness at intermediate (30–60%) levels of habitat amount, and on richness of plants at high (>60%) levels of habitat amount, both of which are mediated by edge effects. Based on these results, we argue that dismissing habitat fragmentation as a powerful force driving species extinction in tropical forest landscapes is premature and unsafe