High within‐ and between‐trunk variation in the nematoceran (Diptera) community and its physical environment in decaying aspen trunks

Abstract

Dead wood is a primary habitat for a large number of insects, including species from many nematoceran (Diptera) groups. The species living in dead wood must be adapted to the ephemeral and ever‐changing nature of their substrate. There is a growing body of knowledge about the effects of dead wood quality and the surrounding landscape on the saproxylic beetle community, but we know very little about the other saproxylic insects. Moreover, we know only very little about the variation in the insect community between different parts of decaying wood pieces. Using emergence traps, we studied the saproxylic nematoceran communities occupying different parts of decaying fallen aspen trunks in a boreal forest. To explain the variation in the detected assemblages, we also studied the variation in the physical environment in different parts of one of the studied trunks during the season. We found out that the overall variation in assemblages was very high and also the similarity between the base and top of the same trunk was usually low. Dissimilarity arose more from differences in species richness than from species turnover. The greatest contrasts in the physical conditions of the study trunk were between the inside and the upper and lower surface of the trunk base. Due to high variation within the trunks and especially between the trunks, the sampling effort in studies on the ecology of saproxylic insects should be high to have a reliable estimate of the local community.

Eleven remarkable Diptera species, emerged from fallen aspens in Kivach Nature Reserve, Russian Karelia

“…Trunk emergence traps have some benefits in comparison with other methods traditionally used for collection of wood-living Coleoptera and Diptera (Alinvi et al 2006, Halme et al 2012). They, however fail in some cases (e.g.…”

“…In Finland and Karelia, so far collected exclusively on aspen (Hancock 2008, Halme et al 2012). According to the authors' data, this species prefers huge wind-broken aspens with a diameter over 70 cm, fallen 7 years ago (Table 1).…”

Resource use of wood-inhabiting fungi in different boreal forest types

“…However, we did not find any species strictly specialized on one particular diameter class. The size of dead wood unit affects the variation of physical conditions, for example temperature (Halme et al 2013) within the wood. Moreover, it is likely that the chemical conditions also vary depending on dead wood size, and those conditions have an effect on how different species are able to utilize the wood (Venugopal et al 2016).…”

Recent noteworthy findings of fungus gnats from Finland and northwestern Russia (Diptera: Ditomyiidae, Keroplatidae, Bolitophilidae and Mycetophilidae)

“…Collected from a decaying aspen tree by using an eclector trap in Finland (as Boletina jamalensis , Halme et al 2013)…”

“…At present the north European fungus gnat fauna is the subject of several intensive taxonomical and ecological investigations (see e.g. Kjaerandsen et al 2007 , Kjaerandsen et al 2009 , Jakovlev 2011a , Søli and Rindal 2012 , Halme et al 2013 , Polevoi 2013a ). Currently, the Checklist of North European (Fennoscandia, NW Russia, Denmark, Iceland) fungus gnats includes 898 species ( Kjaerandsen 2012 ).…”