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Direct and indirect bottom-up and top-down forces shape the abundance of the orb-web spider <i>Argiope bruennichi</i>
Auteur(s)
Bruggisser, Odile T
Sandau, Nadine
Blandenier, Gilles
Fabian, Yvonne
Kehrli, Patrik
Aebi, Alex
Naisbit, Russell E
Bersier, Louis-Félix
Date de parution
2012
In
Basic and Applied Ecology, Elsevier, 2012/13/8/706-714
Résumé
Species abundance in local communities is determined by bottom-up and top-down processes, which can act directly and indirectly on the focal species. Studies examining these effects simultaneously are rare. Here we explore the direct top-down and direct and indirect bottom-up forces regulating the abundance and predation success of an intermediate predator, the web-building spider <i>Argiope bruennichi</i> (Araneae: Araneidae). We manipulated plant diversity (2, 6, 12 or 20 sown species) in 9 wildflower strips in a region of intensive farmland. To identify the major factors regulating the distribution and abundance of<i> A. bruennichi</i>, we quantified three characteristics of vegetation (species diversity, composition and vegetation structure) as well as the spider's prey community and natural enemies. The distribution and abundance of<i> A. bruennichi</i> was regulated by combined bottom-up and top-down processes as well as by direct and indirect interactions between trophic levels. Four main factors were identified: (1) the strong direct effect of vegetation structure, (2) the positive effect of plant species diversity, which affected spider abundance directly and indirectly through increased densities and size of flower-visiting prey species, (3) the positive or negative direct effects of different plant species, and (4) the strongly negative direct effect of predacious hornets. The advantage of taking a global approach to understand the regulation of species abundance is highlighted first by the quantification of the relative importance of factors, with a surprisingly strong effect of hornet predators, and second by the discovery of a direct effect of plant diversity, which raises intriguing questions about habitat selection by this spider.
Identifiants
Type de publication
journal article
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