Colonisation of ephemeral forest habitats by specialised species: beetles and bugs associated with recently dead aspen wood |
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Authors: | Thomas Ranius Petri Martikainen Jari Kouki |
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Institution: | (1) Department of Ecology, Swedish University of Agricultural Sciences (SLU), Box 7044, 750 07 Uppsala, Sweden;(2) School of Forest Sciences, University of Eastern Finland, Joensuu, Finland |
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Abstract: | The most appropriate strategy for preserving fragmented populations depends on a species’ ability to colonise distant habitat
patches. Insects associated with early decay stages of dead wood are expected to have a high capacity to colonise new habitat
patches. To study the dispersal ranges of beetles (Coleoptera) and flat bugs (Hemiptera: Aradidae) dependent on recently dead
aspen (Populus tremula) wood in Finland, we set out 58 piles of recently cut aspen logs at various distances up to 1.6 km from forests that contained
a high density of old aspen trees. We captured insects by trunk window-traps, and counted beetles’ exit holes. Habitat connectivity
was measured in terms of the amount of suitable aspen-wood in the surrounding environment, with the closest dead wood items
up-weighted by a negative-exponential function. The log-piles attracted many saproxylic insects including four red-listed
aspen-specialist species. The exposure of log-piles to the sun, and high levels of habitat connectivity increased the species
richness of aspen-specialists, whereas bark peeling by moose decreased richness. The spatial scale at which species richness
had its strongest response to habitat was 93 m. Among individual species there was a wide variability in spatial scale of
response. This study supports the view that conservation efforts in boreal forests should be concentrated on sites where colonisation
by target species is most likely. Restoration of habitat by re-locating logs may be useful at localities with a rich and specialised
fauna but which have too low rate of formation of dead wood by natural processes. |
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