Summary1. Priority effects have been hypothesized to have long-lasting impact on community structure in natural ecosystems. Long-term studies of priority effects in natural ecosystems are however sparse, especially in terrestrial ecosystems. 2. Wood decay is a slow process involving a high diversity of insect and fungus species. Species interactions that drive change in communities of insects and fungi during wood decay are poorly understood because of a lack of sufficient long-term studies. 3. In this paper, we followed the colonization and succession of wood-living insects and fungi on cut trees during 15 years, from tree death and onwards, in a boreal forest landscape. We test the long-term priority effects hypothesis that the identity and abundance of species that colonize first affect the colonization success of later-arriving species. We also hypothesize that species interact in both facilitative and inhibitory ways, which ultimately affect habitat quality for a red-listed late-succession beetle species. 4. Possible causal associations between species were explored by path analysis. The results indicate that one bark beetle species, Hylurgops palliatus, and one wood-borer species, Monochamus sutor, which colonized the wood during the first year after cutting, influenced the occurrence of a rare, wood-living beetle, Peltis grossa, that started to emerge from the stumps about 10 years later. The positive effects of Hylurgops palliatus and negative effects of M. sutor were largely mediated through the wood-decaying fungus species Fomitopsis pinicola. 5. The study shows that variable priority effects may have long-lasting impact on community assembly in decaying wood. The study also exemplifies new possibilities for managing populations of threatened species by exploring links between early, well-understood species guilds and late, more poorly understood species guilds.
1. Life history traits of solitary nest provisioning bees and wasps (Aculeata) are characterised by low fecundity and extensive parental care. Therefore, it can be expected that egg-laying females are demanding in their nest choice.2. Dead wood in young boreal forest stands in mid-Sweden were surveyed for holes made by different insect species and the occupancy of solitary bees or wasps in those holes was analysed. Artificial nests consisting of wooden poles with pre-drilled holes were used for comparison.3. In 1634 wood objects, 5793 potential nesting holes of 16 types were labelled to insect species or genera that had made the hole. Only 1.8% of these were occupied by any bee or wasp species. In contrast to the natural wood objects, artificial nests had high occupancy (c. 30%).4. Hole diameter, rather than tree species, hole type or stand age, was the most important factor explaining occupancy of a certain aculeate species. Holes in standing dead wood (SDW) had higher occupancy than holes in stumps and logs.5. The results are discussed in the context of aculeate life history traits. It is argued that the reason for the low occupancy in the natural dead wood, especially in the stumps, was that most holes were situated in moist and decayed wood, and offered inferior conditions for offspring during the development from egg to adult.6. Retention and creation of SDW objects of different tree species at final felling is recommended.
Abstract. Contarinia comprises one of the largest genera among gall forming midges of Cecidomyiidae, where identification and species relationships are uncertain. Using data on phenological development, morphometric relationships and mitochondrial DNA, the status of two isomorphic species, C. vincetoxici and C. asclepiadis, which attack the perennial herb Vincetoxicum hirundinaria, were investigated. Data show that they are two distinct species. In rearing experiments, the two gall midges were shown to have different times of adult emergence. Small differences in wing morphology were revealed that separate the two species from each other, as well as from C. loti, the type species of Contarinia. Sequence differences in the mitochondrial cytochrome b gene corroborate the specific status of C. vincetoxici and C. asclepiadis. Furthermore, a phylogenetic analysis, also including three other Contarinia species, showed that the two gall midges on V. hirundinaria are not even the most closely related species, suggesting two separate evolutionary colonizations of the host plant.
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