Werner Topp

Microorganisms and Cellulose Digestion in the Gut of the Woodlouse Porcellio scaber

In the common woodlouse Porcellio scaber different parts of the gut were observed with respect to microbial counts, cellulose activity, and degradation of cellulose. Cellulose is mainly digested in the anterior part of the hindgut, as was indicated by the distribution of cellulolytic activity and the decrease of cellulose content inside the gut. The cellulases woodlice utilize for the degradation of litter are mainly produced by endosymbiotic bacteria in the hepatopancreas rather than by microorganisms ingested with the food. Microorganisms ingested with the litter are digested in the anterior part of the hindgut and may provide an important food source. In the posterior hindgut, bacterial proliferation ensures microbial colonization of feces.

Response of ground-dwelling beetle (Coleoptera) assemblages to giant knotweed (Reynoutria spp.) invasion

Giant knotweeds (Reynoutria spp.) are highly productive and aggressive invaders in riparian wetlands of Europe and North America. We sampled ground-dwelling beetles by pitfall traps from six sites comparing monotypic Reynoutria stands with the invaded native Urtica-dominated stands. Three sites were located in a semi-natural softwood forest and three sites were on a ruderal embankment. The analyses are based on a total of 13,244 individuals from 218 species. Location and site significantly influenced beetle assemblages. Moreover, there were pronounced differences between vegetation stands. The monotypic Reynoutria stands exhibited lower beetle abundance, species richness and rarefaction diversity irrespective of location. However, the negative effect on species richness, abundance and assemblage similarities were stronger on the transformed ruderal embankment than in the semi-natural softwood forest. Reynoutria invasion seems to influence microclimatic conditions. We found a higher abundance of silvicolous and a lower abundance of xerophilous ground beetles in the Reyountria stands than in the Urtica-dominated stands. Feeding guilds reacted differently to Reynoutria invasion that reduced the abundance of predators and herbivores but enhanced that of detritivores. Detritivores assumingly profit from the perennial presence of the large quantities of Reynoutria litter. We conclude that highly productive invaders pauperise the arthropod fauna and alter link strengths in trophic cascades shifting primary producer-based food webs to detritus-based food webs.

Emergence of Coleoptera from deadwood in a managed broadleaved forest in central Europe

We studied Coleoptera emerging from deadwood in a broadleaved forest that has been managed with nature-oriented forestry since 1990 and in which an accumulation of 10 m3 deadwood/ha has been achieved. We sampled a total of 11 m3 of deadwood from oak and beech trees and yielded 32,477 individuals pertaining to 342 species. The number of species emerging from oak deadwood was significantly higher than that from beech. Significantly more species emerged from deadwood with medium size (15–21 cm) diameter than from smaller (5–7 cm) or larger (40–60 cm) diameters. The stage of decay did not influence the number of species during the first 6 years of decomposition. Species richness strongly increased with the amount of deadwood sampled. Species–area regressions yielded z-values of 0.81 for oak and 0.87 for beech deadwood. The beetle assemblage was characterized by a low number of xylophagous species and a high number of mobile zoophagous species. However, two-thirds of the individuals sampled pertained to nine species of Scolytidae. This is why Shannon–Wiener diversity (H) and evenness-indices (E) greatly decreased with increasing number of scolytids. The species and individuals yielded from the sun-exposed deadwood outnumbered those from shaded areas. Namely the scolytid Taphrorychus bicolor reached remarkably high densities in the sun-exposed beech deadwood (>800 individuals/m2). In contrast, oak deadwood never harboured such high numbers of scolytids. Felling of moribund trees had decreased the number of scolytids but it had also considerably reduced the number of rare and endangered species.

Soil fauna of a reclaimed lignite open-cast mine of the Rhineland: improvement of soil quality by surface pattern

Abstract Reclaimed lignite open-cast mine areas in the Rhineland are covered by a mixture of loess and sand deposits containing organic material that originates from the upper quartary soil which has been taken from the front of the mining path. Consequently, the soil fauna that has established itself on the reclaimed open-cast mine areas may result from the primary succession and also from species that are carried to the dumping mines and are able to survive the dumping process. The reclaimed landscape consists of a regular structural pattern of crests and troughs. The troughs provide appropriate habitats for establishing a rich and diverse fauna with higher densities of almost all animal groups investigated, with enhanced microbial activity and higher values of available macronutrients. In terms of plant growth, the physical and chemical conditions found in the troughs exceeded the conditions found on the crests. From laboratory studies we made the following conclusions: (1) environmental conditions in the troughs were improved not only by erosion, but additionally by the soil fauna that directly enhanced microbial activity and indirectly increased the availability of macronutrients; (2) soil animals improved soil quality by increasing the pH-values, increasing the ammonium–nitrogen content and decreasing the content of aluminium ions; and (3) a multiple-species system is able to improve soil quality more effectively than a single-species system.

The role of coprophagy in nutrient release from feces of phytophagous insects

Abstract In microcosms containing soil from a mixed deciduous forest, we examined the nutrient release from feces of phytophagous insects through coprophagous behavior of saprophagous soil animals during 12 weeks of decomposition. The decomposition of feces of Operophthera fagata (Lepidoptera: Geometridae) fed on beech ( Fagus sylvatica ) released more cations (Ca 2+ , Mg 2+ , K + ) into the soil than the decomposition of beech litter, whether or not woodlice, Porcellio scaber and Oniscus asellus (Isopoda: Oniscidea), were present. Similarly, the C/N ratio of the soil was lower in assays with feces than in those with leaf litter. Coprophagy by isopods resulted in decreased C/N ratio of the soil. Respiratory activity of soil microbiota was greater when woodlice degraded Operophthera feces than when they degraded beech litter for 12 weeks. The present study provides evidence for nutrient release from the feces of phytophagous insects into the soil through the feeding activity of coprophagous soil animals.

Responses of the parthenogenetic isopod, Trichoniscus pusillus (Isopoda: Oniscidea), to changes in food quality

Summary Long-term observations of Trichoniscus pusillus revealed that chemical composition and microbial activity of the leaf litter serving as food influenced the reproductive success of females and the mortality rates of juveniles as well. Of the food sources investigated, only alder litter, exhibiting high microbial activity, allowed the maintenance of a stable population with frequently reproducing females. This study concludes that the food type is a significant factor for population parameters of this parthenogenetic isopod. Our results on T. pusillus, belonging to the taxon Synocheta, are compared with data on terrestrial isopod species of the taxon Crinocheta.

Does Porcellio scaber (Isopoda: Oniscidea) gain from coprophagy?

Abstract In feeding experiments, leaf litter of different tree species and isopod feces derived from these leaf litter materials were offered to the common woodlouse, Porcellio scaber . Consumption indices were used to elucidate the nutritional significance of coprophagy. Consumption rates of P. scaber clearly differed between feeding assays with alder ( Alnus glutinosa ) litter and those with isopod feces derived from alder. Differences between feeding assays depended on microbial activity of the food sources when oak ( Quercus robur ) litter or isopod feces derived from oak were offered. Further, microbiota increased the digestibility of oak material, but did not change digestibility of alder litter and reduced digestibility of feces derived from alder. Thus, the significance of litter- or feces-colonizing microbiota decreased with increasing nutritive value of the leaf litter. Inoculated feces derived from oak provided better growth than any other oak-derived food. In contrast, isopods grew better on alder litter than on alder-derived feces. In sum, we found little evidence to support the notion that P. scaber gains from coprophagy. We reject the hypothesis that coprophagy meets a need for nutrients that, due to digestive incapabilities, cannot be satisfied by feeding on leaf litter alone. The hypothesis that microbial colonizers render feces attractive as a source of microbial enzymes or nutrients is only partly corroborated. P. scaber gains from coprophagy through microbial activity or biomass only if leaf litter quality is low.

Correspondence analytical evaluation of factors that influence soil macro-arthropod distribution in abandoned grassland

Summary We analysed field data on the occurrence of woodlice and millipedes in abandoned grassland in southwestern Germany using multivariate ordination statistics to extract information on single environmental factors influencing the distribution of particular species in the field. Different methods (DECORANA, CANOCO) revealed slightly different patterns of ordination, but led to similar conclusions. These conclusions coincide with previously observed ecophysiological requirements of isopods, and confirm the significance of the soil pH for their distribution. Howewer soil pH did not appear to be significant for diplopods. The distribution of diplopod species mainly corresponds with mean annual air temperature. Besides assigning particular species to single study sites that are characterised with respect to environmental factors, we statistically associate a group of three isopod species having similar ecological requirements.

Litter-dwelling beetles in primeval forests of Central Europe: Does deadwood matter?

We investigated the distribution pattern of litter dwelling beetles in four primeval forests of the Western Carpathians. The forests are situated in two mountain ranges and are either southerly exposed oak forests or northerly exposed beech forests. Beetles were extracted from leaf litter of plots close to coarse woody debris (c-CWD) and distant from coarse woody debris (d-CWD). We collected 2946 individuals of 172 species. Plots close to CWD usually were hot spots of species richness and beetle density, which could be increased two-fold and five-fold, respectively, when compared to d-CWD sites. The influence of CWD within each forest type was stronger than that of any other environmental factor. The c-CWD plots were characterised by both a higher presence of common species and a higher number of rare species. Especially, zoophagous and mycetophagous beetles were enhanced. The assemblage wide carrying capacity at c-CWD sites varied in respect to the gradients of temperature and moisture within a forest. A longer gradient provided a higher carrying capacity. We assume that the influence of downed deadwood on litter dwelling beetles will also be effective in commercial forests and stop the downward spiral with continuing loss of species.

The distribution pattern of centipedes in four primeval forests of central Slovakia

We investigated the distribution pattern of centipedes (Chilopoda) in four primeval forests of the western Carpathians, central Slovakia. The forests are located in two different mountain ranges (Kremnické vrchy and Pol’ana Mountains), which are exposed on either the southern (Boky, Rohy) or northern slopes (Pol’ana, Badín). In these forests, the influence of coarse woody debris (CWD) on centipede distribution was studied, by distinguishing sampling sites on the forest floor, close to CWD (c-CWD) and distant from CWD (d-CWD). In total, we collected 2,706 individuals from 20 species of centipedes. Average species richness and number of individuals per forest ranged from 8 to 12 species/m2 and from 244 to 486 individuals/m2. The oak forests on south facing slopes harboured several species, which did not occur in the more northern exposed fir-beech forests. Number of species as well as individuals, however, varied more within than between individual forests. Increase of species number and density was mainly caused by CWD and was more pronounced on the southern slopes (P<0.001), characterized by high temperatures and low precipitation, than on the northern slopes (n.s. to P<0.01), characterized by low temperatures and high precipitation. It was found that CWD did not generally increase (species) diversity.