Do species interactions prevent Limoniscus violaceus from living in suitable basal hollow trees?

The violet click beetle (Limoniscus violaceus) is an endangered beetle that is protected in Europe. Its conservation required better knowledge on its biology. Recently, a study revealed that the probability of occurrence of L. violaceus in hollows increases with increasing tree circumference at 30 cm above ground and with increasing hollow decay stage (Gouix et al., submitted). However, the model showed that it was easier to identify unoccupied hollows than to identify the occupied ones. As tree hollows harbour a ränge of associated and facultative species living within a relatively small habitat, we may suspect some species interactions (competition and/or predation) that prevent Limoniscus violaceus from occupying suitable basal hollow trees. We studied beetle and Spider assemblages emerging from 73 basal hollow trees located within a Single forest site of 3500 ha (in France). All trees were considered to be suitable for Limoniscus violaceus (i.e. trees with a circumference at 30 cm above ground greater than 235 cm and cavity at an advanced stage of decay). We used the probabilistic approach to test for statistically significant pair-wise patterns of species co-occurrence. In total, 4805 species pairs were analyzed and 9.6 % had non-random patterns. We detected very few negative co-occurrence patterns (19) compared with positive ones (444). Regarding Limoniscus violaceus, we highly linked to the presence of tree hollows in mature trees. Moreover, the interaction between saproxylic insects and hollows shows specialised interacting patterns that model the structure and stability of these saproxylic assemblages. The objective of this work is to evaluate how interacting patterns of saproxylic insect networks vary according to woodland sites. We selected three representative Mediterranean woodlands in the Park: one sclerophyllous oak woodland of Quercus rotundifolia; one mixed deciduous oak woodland of Quercus pyrenaica and Quercus faginea; and one ash riparian woodland of Fraxinus angustifolia. We considered 30, 30 and 27 tree hollows, respectively, which were covered with emergence traps. Our study lasted one year, during which traps were emptied monthly and pots were replaced. We selected Coleoptera and Syrphidae (Diptera) as study groups. They were sorted according to trophic guilds: xylophagous, saproxylophagous, saprophagous, xylomycetophagous and predators. We used Aninhado and Modular programmes to evaluate the network architecture, and bipartite for R programme to study interacting attributes in the hollow-saproxylic insect interaction in each woodland site. Saproxylic insect-hollow networks presented a significant nested pattern, which means that most of the interactions are established with the most generalist nodes/species at both trophic levels (in this case, the lower trophic level is composed of hollows and the higher trophic level is composed of insects). Not all studied forests showed the same level of connectance (proportion of possible links between trees and species), the deciduous oak woodland being the forest with the most densely interconnected network

Data from: Suppression of overlearning in independent component analysis used for removal of muscular artifacts from electroencephalographic records

This paper addresses the overlearning problem in the independent component analysis (ICA) used for the removal of muscular artifacts from electroencephalographic (EEG) records. We note that for short EEG records with high number of channels the ICA fails to separate artifact-free EEG and muscular artifacts, which has been previously attributed to the phenomenon called overlearning. We address this problem by projecting an EEG record into several subspaces with a lower dimension, and perform the ICA on each subspace separately. Due to a reduced dimension of the subspaces, the overlearning is suppressed, and muscular artifacts are better separated. Once the muscular artifacts are removed, the signals in the individual subspaces are combined to provide an artifact free EEG record. We show that for short signals and high number of EEG channels our approach outperforms the currently available ICA based algorithms for muscular artifact removal. The proposed technique can efficiently suppress ICA overlearning for short signal segments of high density EEG signals

Is active management the key to the conservation of saproxylic biodiversity? Pollarding promotes the formation of tree hollows.

Trees with hollows are key features sustaining biodiversity in wooded landscapes. They host rich assemblages of often highly specialised organisms. Hollow trees, however, have become rare and localised in Europe. Many of the associated biota is thus declining or endangered. The challenge of its conservation, therefore, is to safeguard the presence of hollow trees in sufficient numbers. Populations of numerous species associated with tree hollows and dead wood are often found in habitats that were formed by formerly common traditional silvicultural practices such as coppicing, pollarding or pasture. Although it has been occasionally mentioned that such practices increase the formation of hollows and the availability of often sun-exposed dead wood, their effect has never been quantified. Our study examined the hollow incidence in pollard and non-pollard (unmanaged) willows and the effect of pollarding on incremental growth rate by tree ring analysis. The probability of hollow occurrence was substantially higher in pollard than in non-pollard trees. Young pollards, especially, form hollows much more often than non-pollards; for instance, in trees of 50 cm DBH, the probability of hollow ocurrence was ∼0.75 in pollards, but only ∼0.3 in non-pollards. No difference in growth rate was found. Pollarding thus leads to the rapid formation of tree hollows, a habitat usually associated with old trees. It is therefore potentially a very important tool in the restoration of saproxylic habitats and conservation of hollow-dependent fauna. If applied along e.g. roads and watercourses, pollarding could also be used to increase landscape connectivity for saproxylic organisms. In reserves where pollarding was formerly practiced, its restoration would be necessary to prevent loss of saproxylic biodiversity. Our results point to the importance of active management measures for maintaining availability, and spatial and temporal continuity of deadwood microhabitats

Data from: Is active management the key to the conservation of saproxylic biodiversity? Pollarding promotes the formation of tree hollows

Trees with hollows are key features sustaining biodiversity in wooded landscapes. They host rich assemblages of often highly specialised organisms. Hollow trees, however, have become rare and localised in Europe. Many of the associated biota is thus declining or endangered. The challenge of its conservation, therefore, is to safeguard the presence of hollow trees in sufficient numbers. Populations of numerous species associated with tree hollows and dead wood are often found in habitats that were formed by formerly common traditional silvicultural practices such as coppicing, pollarding or pasture. Although it has been occasionally mentioned that such practices increase the formation of hollows and the availability of often sun-exposed dead wood, their effect has never been quantified. Our study examined the hollow incidence in pollard and non-pollard (unmanaged) willows and the effect of pollarding on incremental growth rate by tree ring analysis. The probability of hollow occurrence was substantially higher in pollard than in non-pollard trees. Young pollards, especially, form hollows much more often than non-pollards; for instance, in trees of 50 cm DBH, the probability of hollow ocurrence was ~0.75 in pollards, but only ~0.3 in non-pollards. No difference in growth rate was found. Pollarding thus leads to the rapid formation of tree hollows, a habitat usually associated with old trees. It is therefore potentially a very important tool in the restoration of saproxylic habitats and conservation of hollow-dependent fauna. If applied along e.g. roads and watercourses, pollarding could also be used to increase landscape connectivity for saproxylic organisms. In reserves where pollarding was formerly practiced, its restoration would be necessary to prevent loss of saproxylic biodiversity. Our results point to the importance of active management measures for maintaining availability, and spatial and temporal continuity of deadwood microhabitats

Sebek_et_al_Pollarding

Comparison of hollow formation between pollard and unmanaged trees. The worksheet "Hollow incidence" gives information on presence/absence (1/0)of hollows (cavities) in trees. The worksheet "Incremental growth" contains measurements of tree rings from 8 pollard and 10 unmanaged trees. See the article for more information on study design

Forms of pollard and unmanaged trees.

<p>A pollard (A) and an unmanaged tree (B), shown with their most common type of tree hollows (grey colored): hollows formed in the upper parts of the trunk as a result of bared heartwood after pruning are common in pollards, whereas hollows formed after a branch fall are the most common hollow type in unmanaged trees.</p

Radial growth of willows.

<p>Mean radial growth of pollards (solid line; n = 8) and unmanaged willows (dashed line; n = 10) at the Pastvisko site, Czech Republic. Although pollard willows show increased growth rates after the pollarding event of 2003 (vertical dashed line), the pattern was not significant in our study.</p