Browsing by Autor "Diederik Strubbe"

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Bird species richness in High-Andean forest fragments: habitat quality and topography matter
(2020) Constance Fastré; Diederik Strubbe; José Antonio Balderrama; Jennifer R. A. Cahill; Hannes Ledegen; Mauricio Torrico Orellana; Erik Matthysen
Montane forests worldwide are known centers of endemism and biodiversity but are highly threatened by fragmentation processes. Using data collected in 15 Polylepis forest remnants covering 2000 hectares, we investigated how bird species richness and bird community composition, particularly for species of conservation concern, are influenced by habitat quality and topography in the Tunari National Park in the High Andes of Bolivia. Bird species richness was highest in topographically complex, low-elevation Polylepis patches located in areas with a high potential to retain rainwater. Bird communities differed strongly between Polylepis lanata and P. subtusalbida remnants, each supporting different threatened and endemic species. Within the P. subtusalbida forest, high-elevation fragments characterized by high amounts of sunlight and low anthropogenic disturbance were more likely to contain threatened species. Surprisingly, we found no effect of fragment size on the diversity or composition of bird communities or the presence of bird species of conservation concern. The presence of exotic plantations (Pinus and/or Eucalyptus spp.) in or outside forest remnants was negatively associated with the number of bird species as well as with occurrence of the endangered Cochabamba-mountain finch (Compsospiza garleppi). To support the different communities found in Polylepis forests, these results suggest that conservation efforts should be directed towards both forest types (P. subtusalbida and P. lanata) present in the area. For an efficient management of avian diversity, exotic plantations should be established away from native remnants while existing patches should be managed to maintain or increase habitat quality. Finally, the importance of local topography in determining avian species richness and community composition in forest fragments, mainly through topographic controls on moisture distribution and the amount of sunlight received by the fragments, should be considered when planning conservation and reforestation schemes.
Effects of variable selection on modelling habitat and potential distribution of the Andean bear in Bolivia
(2013) Ximena Velez–Liendo; Diederik Strubbe; Erik Matthysen
Species distribution models are used in ecology and conservation biology to draw inferences about the drivers of species' ranges. However, poor conceptual background, environmental variable selection, and algorithm selection can contribute to misleading model predictions. We assessed the effects of environment variable selection and compared statistical performance and output maps of correlative resource- and biotope-based models for estimating the habitat and potential distribution of the Andean bear (Tremarctos ornatus) in Bolivia's Tropical Andes. The resource-based approach estimated bear habitat using 7 resources associated with 3 ecological functions: feeding, shelter, and access to water. In contrast, the biotope model described the habitat by applying 11 environmental predictors related to topography, vegetation, and human activities. Both models performed equally well overall and better than random, with shelter as the most influential variable for the resource model and Yunga forest for the biotope model. However, discrepancies in the extent and arrangement of predicted bear distribution between models differed and emphasized the effect of variable selection, which could influence the delineation of conservation areas for this species. We suggest using a resource-based approach when modelling species distribution because of the more direct relationship to the species investigated and greater ease of interpreting results.