Contrasting Responses of Saproxylic Insects to Focal Habitat Resources: The Example of Longhorn Beetles and Hoverflies in Belgian Deciduous Forests |
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Authors: | Philippe Fayt Marc Dufrêne Etienne Branquart Pierre Hastir Christophe Pontégnie Jean-Marc Henin Veerle Versteirt |
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Institution: | (1) Research Centre of Nature, Forests and Wood (CRNFB), Av. Maréchal Juin 23, B-5030 Gembloux, Belgium;(2) Biodiversity Research Centre, Catholic University Louvain (UCL), Croix du sud, 4-5, B-1348 Louvain-La-Neuve, Belgium;(3) Forest and Nature Management Unit, Gembloux Agricultural University (FSAGx), Passage des Déportés 2, B-5030 Gembloux, Belgium;(4) Department of Entomology, Royal Belgian Institute of Natural Sciences (IRSNB), Vautierstraat 29, B-1000 Brussels, Belgium |
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Abstract: | Although both saproxylic longhorn beetles and hoverflies benefit from the presence of woody substrates for reproduction, they
differ in their requirements for floral resources and for microbiotopes of overmature and senescent trees. This led us to
expect contrasting responses between the two species groups in relation to these essential resources. We examined this prediction
in 22 mature oak- and beech-dominated stands of southern Belgium by relating their species assemblages to local vegetation
structure and composition, altitude and landscape composition. Stands were organised in pairs as a function of their overall
dead wood supply. Free-hanging window traps, stump emergence traps and Malaise traps produced 30 longhorn beetle species (1637
individuals) and 106 hoverfly species (3020 individuals). Paired-comparisons controlling for annual variation in captures
showed that, unlike saproxylic hoverflies, stands with dead wood hosted more species and individuals of longhorn beetles.
Accordingly, the two species groups were found to be independent on ordination axes, responding to different sets of environmental
conditions. While stands dominated by oaks with a high snag volume were highly favoured by longhorn beetles, saproxylic and
threatened syrphids were limited to open-stands with large trees and a well-developed, species rich herb layer providing the
floral resources required for their reproduction. Our results suggest that, when defining criteria to identify or restore
important habitats for saproxylic insect conservation, variables related to different aspects of dead wood supply should not
be the only criteria taken into account. |
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Keywords: | Cerambycidae Flower resources Microhabitat Saproxylic Syrphidae |
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