Browsing by Author "Gaese, Katrin B."

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    Bats are Not Birds – Different Responses to Human Land-use on a Tropical Mountain
    (2015-05) Bonitz, Maria H. B.; Ferger, Stefan W.; Gaese, Katrin B.; Tschapka, Marco; Howell, Kim; Kalko, Elisabeth K. V.
    Land-use intensification has consequences for biodiversity and ecosystem functioning, with various taxonomic groups differing widely in their sensitivity. As land-use intensification alters habitat structure and resource availability, both factors may contribute to explaining differences in animal species diversity. Within the local animal assemblages the flying vertebrates, bats and birds, provide important and partly complementary ecosystem functions. We tested how bats and birds respond to land-use intensification and compared abundance, species richness, and community composition across a land-use gradient including forest, traditional agroforests (home garden), coffee plantations and grasslands on Mount Kilimanjaro, Tanzania. Furthermore, we asked how sensitive different habitat and feeding guilds of bats and birds react to land-use intensification and the associated alterations in vegetation structure and food resource availability. In contrast to our expectations, land-use intensification had no negative effect on species richness and abundance of all birds and bats. However, some habitat and feeding guilds, in particular forest specialist and frugivorous birds, were highly sensitive to land-use intensification. Although the habitat guilds of both, birds and bats, depended on a certain degree of vegetation structure, total bat and bird abundance was mediated primarily by the availability of the respective food resources. Even though the highly structured southern slopes of Mount Kilimanjaro are able to maintain diverse bat and bird assemblages, the sensitivity of avian forest specialists against land-use intensification and the dependence of the bat and bird habitat guilds on a certain vegetation structure demonstrate that conservation plans should place special emphasis on these guilds.
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    Food resources and vegetation structure mediate climatic effects on species richness of birds
    (2014-04) Ferger, Stefan W.; Schleuning, Matthias; Andreas, Hemp; Howell, Kim; Gaese, Katrin B.
    Aim Climate is widely recognized as a major predictor of species richness patterns along large-scale environmental gradients. Nevertheless, the mechanisms by which climate influences species richness are still a matter of debate. We disentangle whether climate influences species richness of birds directly via physiological limi-tations or indirectly via vegetation structure or the availability of food resources. Location Mount Kilimanjaro, Tanzania. Methods We recorded bird species richness along an elevational gradient from 870 to 4550 m a.s.l. We quantified local climatic conditions, vegetation structure and the availability of food resources, and applied path analysis to disentangle their direct and indirect effects on species richness of all birds, frugivores and insectivores. Results Overall, we recorded 2945 individuals from 114 bird species. Species richness of all birds was closely correlated with temperature, vegetation structure and invertebrate biomass and both direct and indirect (via vegetation structure and availability of food resources) climatic effects were important for the diversity of the whole, trophically heterogeneous bird community. The species richness of insectivorous birds was linked to vegetation structure and invertebrate biomass, while the richness of frugivores was strongly associated with fruit abundance. Climatic factors influenced bird species richness of both avian feeding guilds exclu-sively indirectly via vegetation structure and availability of food resources. Main conclusions We reveal the importance of trophic interactions for gener-ating species richness patterns along large-scale environmental gradients. Our results challenge the general assumption that temperature and water availability influence species richness mostly directly, and underscore the importance of veg-etation structure and the availability of food resources as principal mediators of climatic effects on species