2 research outputs found
Cavity occurrence and use by hole-nesting birds in Pyrenean managed oak forests
Tese de mestrado, Biologia (Biologia da Conservação), 2009, Universidade de Lisboa, Faculdade de CiênciasResumo alargado em português disponível no documentoThis study examines cavity occurrence and use by hole-nesting birds in managed Pyrenean oak (Quercus pyrenaica) forests in the southern Cantabrian Mountains (NW Spain). In 2007, cavity occurrence and use were assessed in 12 plots (6 in old forests, 6 in young forests), covering a total area of 97ha. Overall, 720 cavities from 466 trees were assessed. Generalized Linear Mixed Models (GLMMs) results showed that cavity trees were significantly larger than non-cavity-trees. Besides, cavity-trees were decayed in a significantly higher proportion than non-cavity-trees. Large decayed trees provided woodpeckers with suitable substrate for excavation, and were also a source of nonexcavated natural cavities. For nesting, birds preferred living trees, longer cavity depths, cavities with narrower entrances, woodpecker-created cavities and smaller diameter trees. The smaller holes may be preferred to avoid the access of medium and large sized predators. Similarly, deeper cavities may prevent predators from reaching them to remove chicks. Even if woodpecker-created cavities were preferred by birds, most of the cavities were not created by woodpeckers and only a small proportion of woodpecker-created cavities were used by birds (12%), so the role of woodpecker as keystone species in this area could not be confirmed. The preference for living trees may be related to cavity microclimate stability, as living trees heat and cool more slowly than decayed trees, leading to more stable temperatures. The preference for cavity-trees with smaller diameter may be due to the presence of large decayed trees unable to hold a nest. Taking into account that cavity-trees had larger diameters than non-cavity-trees, and that trees occupied by birds were smaller than non-occupied cavity-trees, many birds occupied medium-size trees. Nest-entrance tended to be oriented to East-Southeast, perhaps because such sunny orientations help to warm young and keep the cavity dry. Cavity and nest densities were higher in old forests in relation to young forests, perhaps because old forests provide higher availability of large decayed trees, which are important sources of cavities. Overall, occupation was low (19%), which may be due to the presence of a high proportion of low quality cavities which were unsuitable for nesting. Alternatively, intra- and interspecific territoriality may lead to low occupation rates of cavitie
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The effects of climate and land abandonment on Iberian bees
The emerging threat of pollinator declines has motivated research on bee ecology to understand the causes of declines and to develop appropriate conservation strategies. The main drivers of decline are anthropogenic and include: loss of habitat to agricultural intensification; use of pesticides; climate change; and alien species. However, in many parts of the world, knowledge of bee ecology and spatial distributions is scarce and the impacts of these stressors on bee populations are poorly understood. The Iberian Peninsula, located in the south-western part of Europe is one of the regions in Europe where there is large knowledge gap in relation to bee distribution and their conservation status. Additionally, the region has experienced the expansion of farmland abandonment in remote areas due to poor soils and rural depopulation. This thesis investigates how bee distributions in the Iberia Peninsula are shaped by climate using innovative tools such as Species Distribution Modelling (SDMs). It also evaluates how farmland abandonment shapes bee communities and their ecological interactions along an environmental gradient. The main findings reveal a) the climatic distributions of bumblebees, highlighting under-sampled areas in Iberia where rare species are likely to occur; b) the negative effect of land abandonment on bees in the intermediate successional stages such as shrublands; c) great beta diversity, with higher differences in species composition between sites (ßRepl) in early-successional stages such as grasslands d) plant-bee interactions become more specialized along a secondary succession triggered by land abandonment. Overall, this thesis provides novel information on the ecology of bees and proposes the best management practices for Iberian bee conservation including the need to control the proliferation of intermediate successional stages in the landscape while preserving grasslands and forests