Morphological modifications among oribatid mites (Acari: Oribatida) in relation to habitat differentiation in mangrove forests

We examined morphological modifications among oribatid species in five microhabitats in mangrove forests in the Ryukyu Islands of Japan. A total of 89 oribatid species were recorded from canopy (leaves and branches), bark of flooded trunks (trunks of 0–50 cm high and knee roots), bark of other trunks higher than 50 cm, and littoral algae in mangrove forests, and the forest-floor soil in an adjacent bank forest. There were no significant differences in the body length, body width, and notogastral length among oribatid species from the five microhabitats. The mean sensillus length of the oribatid species from the forest-floor soil was about twice as long as that from the other microhabitats. Claw morphology was characterized by two attributes: number (monodactyly and tridactyly) and length. In the canopy and trunks, the proportion of tridactyl species was higher than that of monodactyl species. On the other hand, the proportion of tridactyl species in the forest-floor soil accounted for only about 20%, and that in the flooded trunks and littoral algae approximated to zero. The mean claw length was larger in the oribatid species from the flooded trunks and littoral algae than in both monodactyl and tridactyl species from every other microhabitat. Trydactyl species with short claws in the arboreal environments might have been selected by a compromise between grip and mobility for unpredictable environmental changes such as wind and rain. The dominance of monodactyl species with a longer claw in the littoral environments implies a consequence of selection for regular tidal flooding, which requires oribatids to grip tighter on the substrate. The modifications in claw morphology of oribatid mites in mangrove forest might be interpreted as adaptations to a difference in the predictability of the environmental conditions of microhabitats.     

Little effect of forest age on oribatid mites on the bark of trees

This study investigates the effect of forest age (20-, 50-, 160-year-old, and primeval forest) on oribatid mite communities on the bark of oak trees in the National Park Pusza Białowieża in eastern Poland. We hypothesized that oribatid mite diversity on bark peaks at forests of intermediate age and that the number of parthenogenetic species of oribatid mites is highest in young stands. In contrast to these hypotheses, the diversity, density, number of juveniles, community structure and the mode of reproduction of oribatid mite species were not significantly affected by forest age. None of the oribatid mite species occurred exclusively on trees of a specific age. The results suggest that oribatid mite communities on the bark of trees are minimally affected by tree harvesting regimes. In contrast to oribatid mites in soil, communities on bark appear to be less sensitive to disturbances.     

Microhabitats of Collembola (Insecta: Entognatha) in beech and spruce forests and their influence on biodiversity

Collembolan communities were studied in 41 microhabitats in beech and spruce forests of south ( ofín and umava) and central (Jevany) Bohemia. The communities of Collembola were analysed using TWINSPAN and CANOCO programs. The aim of this study was to establish differences between patch (microhatitat) communities and the main forest community in spruce and beech forests, the differences between both types of forests and among different regions of Bohemia. Further questions were: is there a difference in microhabitat communities during secondary forest succession? do some species live exclusively in one or few microhabitats? and does microhabitat diversity influence the biodiversity in forest soils? Material comprising  25 590 specimens of Collembola belonging to 142 species was analysed. Highly significant differences were determined between microhabitat communities in beech and spruce forests, as well as among forests in different regions of Bohemia. Significant differences were also found among microhabitats in forests of different ages. Also, some microhabitat communities of Collembola, e.g. moss on boulders, were significantly different from their main forest community. Certain collembolan species existed exclusively in one or two microhabitats. Patches therefore influenced substantially biodiversity in these forest soils.     

Oribatid mite and collembolan diversity, density and community structure in a moder beech forest (Fagus sylvatica): effects of mechanical perturbations

The effects of mechanical perturbations on two soil microarthropod communities (oribatid mites and collembolans) were investigated in a moder beech forest on sandstone. We disturbed the soil matrix by sieving and mixing the litter and soil of the moder profile. The top litter layer (L material) and the deep mineral soil (Bv) remained intact. Three amounts of disturbance were established: a single perturbation, perturbations once every 2 months (60 d) and once every 2 weeks (14 d). Densities of most groups of oribatid mites and all groups of collembolans declined in the disturbance treatments. In most cases, densities were lowest in the strong perturbation treatment (14 d). Desmonomata were the only group of oribatid mites that benefited from intermediate amounts of disturbance but not from the strongest disturbance. Also, disturbances reduced diversity of oribatid mites and collembolans. According to their sensitivity to disturbances oribatid mites ranked Poronota=Enarthronota=Suctobelbidae (the most sensitive)>Oppiidae>Tectocepheus>Desmonomata. The ranking of collembolans was Folsomia (the most sensitive)>Hypogastruridae/Neanuridae>Onychiuridae=Isotomidae>Entomobryidae. Generally, tolerance of disturbance was wider for oribatid mites than for collembolans. The results indicate that disturbances such as mixing of litter and soil and comminution of litter material strongly affect the density and diversity of soil microarthropods. However, they also indicate that the soil microarthropod community is resistant to weaker disturbances. In the field, mechanical disturbances are often caused by burrowing of earthworms. Our results suggest that the high density of microarthropods in moder soils may be due to the low intensities of mechanical disturbances by earthworms.     

Wind dispersal of oribatid mites as a mode of migration

Oribatid mites are important colonizers of young soils, but little is known about their immigration pathways. In this study, one often-stated hypothesis was tested quantitatively: that wind is an important dispersal pathway. The aim was (1) to detect wind dispersal in oribatid mites (using sticky traps at different heights above ground level) and to determine factors influencing wind dispersal, (2) to investigate whether oribatids can survive wind dispersal and immigrate by wind into young soils (using mini-pitfall traps in test plots with oribatid-free substrate, active immigration being prohibited) and (3) to find out whether those oribatids are able to colonize young soils (using soil cores from the test plots). The results demonstrate (1) that mainly arboreal oribatid species were dispersed by wind - even at 160 m height - and can therefore be spread over large distances. Nevertheless, about 10% of the wind-dispersed oribatid mites belonged to species able to live in the soil and may therefore be potential colonizers of young soils. The number of specimen and species transported by wind was the highest close to the soil surface and the number of dispersed individuals was mainly influenced by seasonality and humidity. The results also suggest that the probability of a soil oribatid being dispersed by wind depends on its original microhabitat (tree habitats > soil surface > deeper soil layers) and its body weight. It was also shown that soil-dwelling oribatid mites survived wind dispersal and immigrated by wind into the test plots and that colonization of the test plots took at least 2 months longer than immigration. However, colonization success was low during the first 2 years of investigation and only Trichoribates incisellus was found several times in the nutrient-poor substrate. Therefore, wind dispersal is an important migration pathway, especially for arboreal oribatids. We suggest that immigration into young soils most likely occurs by repeated short-distance dispersal. Only some species are able to survive the hostile conditions of wind dispersal as well as of pioneer soils, but those that do are potentially the founders of new populations.     

Variation between mite communities in Irish forest types – Importance of bark and moss cover in canopy

Extensive afforestation took place in Ireland during the twentieth century and the forest cover currently represents about 10% of the land area. However, approximately 50% of this forest is Sitka spruce, a non-native species introduced from the North Western United States of America. Little is known about the microarthopods of these forests and the current study examined the mites (Oribatida and Gamasina) occurring in the canopy, moss (both on the soil surface and in the canopy) and soil of oak, ash, Scots pine and Sitka spruce forests in Ireland to compare the mite assemblages in each and to determine the associations between forest type and the form of constituent microhabitats in determining the structure of this fauna. There were significant differences between the diversity and species composition of the assemblages in the different forest types with the largest species richness occurring in oak forest and the smallest in first rotation Sitka spruce forest. Analysis of our data, together with the results from other studies, suggest that the differences arise because the variation between the architecture of the tree species is reflected in the structure of microhabitats such as the form of the bark and the extent of moss cover. Thus while the ultimate factors affecting the variation in the mite fauna may be the form of the microhabitats, these are intrinsic properties of the forests associated directly with the species of tree. Finally, our results do not support the view that exotic species will necessarily have low biodiversity of mites than native forests.     

Spatial patterns of variation in the composition and structure of nematode communities in relation to different microhabitats: a case study of Quercus dalechampii Ten. forest

Variability in the spatial distribution of nematode communities in relation to the structural heterogeneity of the environment was studied in nine different microhabitats within a relatively small area of a natural oak forest in Bulgaria. Maturity and diversity indices, trophic structure and the distribution of colonizer-persister groups were applied to analyze the quality of substrate and ecological processes involved from a functional point of view. Two main groups of nematode communities, below- and above-ground, were distinguished in terms of the location of the microhabitats. Our results indicated a higher percentage similarity between nematode communities inhabiting microhabitats with a higher resemblance in substrate structure, and abiotic and biotic conditions than between microhabitats with more dissimilar microenvironmental conditions. The application of Detrended Correspondence Analysis helped to reveal two ecological gradients. The first one was from microhabitats characterized by smaller fluctuations in microclimatic conditions and nutrient supply to microhabitats with more adverse abiotic conditions and dynamics of food resources. Along this gradient from below- to above-ground microhabitats, the proportion of general opportunists (cp 2 taxa) increased, whereas the diversity, MI and the proportions of persisters (cp (3-5) taxa), decreased. Along the second gradient a gradual decrease in the decomposition rate within above-ground microhabitats was revealed, which was indicated by the proportion of enrichment opportunists (cp 1 taxa). The nematode communities of decaying wood had the most specific cp groups' distribution characterized by a high proportion of enrichment opportunists (colonizers). Each microhabitat has developed nematode communities with a characteristic trophic structure that was related to the relative importance of primary production and decomposition processes occurring within the microhabitat. The nematode communities of mosses growing on soil, stones and tree trunks had similar trophic structure dominated by bacterial-feeding nematode taxa. Our results supported the role of nematode communities as potential indicators of environmental conditions.     

Changes in the community composition and trophic structure of microarthropods in sporocarps of the wood decaying fungus Fomitopsis pinicola along an altitudinal gradient

Soil microarthropods colonize a wide range of habitats including microhabitats such as earthworm burrows, ant nests, tree trunks, moss mats and wood decaying fungi. While many of these microhabitats have been investigated intensively, the role of wood decaying fungi as a habitat and food resource for microarthropods found little attention. We investigated the density, community structure, reproductive mode and trophic structure of microarthropods, in particular oribatid mites, in the wood decaying fungus Fomitopsis pinicola (Schwarts: Fr) Karst. along an altitudinal gradient in Germany spanning from 350 m to 1160 m. Microarthropods were extracted from sporocarps, and stable isotope ratios (¹⁵N/¹⁴N; ¹³C/¹²C) of the fungus and the microarthropods were measured. Densities of most microarthropod taxa were highest at lower altitudes and decreased with increasing altitude. Oribatid mites were the dominant animal taxon. Their community structure gradually changed with altitude. Stable isotope ratios indicated that oribatid mite and other arthropod species occupy distinct trophic niches but most do not feed on F. pinicola. Notably, species of the same genus, e.g. Carabodes, occupied different trophic niches. Most oribatid mite species in F. pinicola reproduced sexually which is similar to the bark of trees but in contrast to the soil where most species reproduce via parthenogenesis. The findings indicate that (1) at high altitudes microarthropod density in fungal fruiting bodies is limited by low temperatures reducing animal metabolism and reproduction, and this also affects oribatid mite community structure, (2) despite the uniform habitat trophic niches of oribatid mite species differ and this also applies to morphologically similar species of the same genus, and (3) feeding on F. pinicola or associated resources facilitates the dominance of sexual reproducing species.     

Canopy Oribatida: Tree specific or microhabitat specific?

A diverse assemblage of oribatid mites inhabits the canopy of coniferous trees in western North America. We tested the hypothesis that oribatid mites are microhabitat specific in old-growth Douglas fir, Western hemlock and western redcedar at the Wind River Crane Canopy Research Facility, Washington, USA. The upper 3 m of canopy of the three tree species were accessed using the canopy crane. Oribatida were extracted from 4 to 12 g dwt samples of alecterioid and foliose lichens using the twig-washing technique. Overall species richness was low, 16 species representing 11 families, with no species unique to this site. Species were absent from samples taken contemporaneously from the forest floor. All oribatid species were found in foliose lichens, whereas only nine species, in seven families, were recovered from alecterioid lichens. Oribatid species richness was lichen specific depending on the tree species. On Western hemlock both lichens supported similarly rich communities, but on Douglas fir and western redcedar foliose lichens supported the richer community.     

Small-scale plant species richness and evenness in semi-natural grasslands respond differently to habitat fragmentation

The study explores whether small-scale species diversity, species evenness and species richness in semi-natural grassland communities are similarly associated with present management regime and/or present and historical landscape context (percentage of different land-cover types in the surroundings). Species diversity, evenness and richness were recorded within 441 50 × 50 cm grassland plots in 4.5 × 4.5 km agricultural landscape on Öland, Sweden. Recent and historical land-cover maps (years 2004, 1959, 1938, 1835, and 1800) were used to characterize the present and past landscape context of the sampled vegetation plots. Partial regression and simultaneous autoregressive models were used to explore the relationships between species diversity measures (Shannon diversity, richness and evenness) and different explanatory variables while accounting for spatial autocorrelation in the data. The results indicated that species richness was relatively sensitive to grassland isolation, while the response of species evenness to isolation was characterized by a degree of inertia. Because the richness and evenness components of species diversity may respond differently to habitat fragmentation, we suggest that monitoring projects and empirical studies that focus on changes in biodiversity in semi-natural grasslands should include the assessment of species evenness - as a complement to the assessment of species richness. In addition, our results indicated that the development and persistence of a species-rich and even grassland vegetation was favoured in areas that have historically (in the 19th century) been surrounded by grasslands. Information on landscape history should, whenever possible, be incorporated into the planning of strategies for grassland conservation.     

Influence of tree characteristics and forest management on tree microhabitats

Higher densities of tree microhabitats in unmanaged forests may explain biodiversity differences with managed forests. To better understand the determinants of this potential biodiversity indicator, we studied the influence of tree characteristics on a set of tree microhabitats (e.g. cavities, cracks, bark features) on 75 plots in managed and unmanaged French forests. We hypothesized that the number of different microhabitat types per tree and the occurrence of a given microhabitat type on a tree would be higher in unmanaged than in managed forests, and that this difference could be linked to individual tree characteristics: diameter, vitality and species. We show that unmanaged forests contained more trees likely to host microhabitats (i.e. large trees, snags) at the stand level. However, at the tree level, forest management did not influence microhabitats; only tree characteristics did: large trees and snags contained more microhabitats. The number and occurrence of microhabitats also varied with tree species: oaks and beech generally hosted more microhabitats, but occurrence of certain types of microhabitats was higher on fir and spruce. We conclude that, even though microhabitats are not equally distributed between managed and unmanaged forests, two trees with similar characteristics in similar site conditions have the same number and probability of occurrence of microhabitats, whatever the management type. In order to preserve biodiversity, foresters could reproduce unmanaged forest features in managed forests through the conservation of specific tree types (e.g. veteran trees, snags). Tree microhabitats could also be more often targeted in sustainable forest management monitoring.     

Tree identity surpasses tree diversity in affecting the community structure of oribatid mites (Oribatida) of deciduous temperate forests

The role of tree diversity and identity as determinants of soil animal community structure is little understood. In a mature deciduous forest dominated by beech we identified clusters of one, two and three tree species of beech, ash and lime allowing to investigate the role of tree species diversity and identity on the density and community structure of oribatid mites. To relate oribatid mite community structure to environmental factors we measured leaf litter input, fine root biomass, mass of organic layers, topsoil pH and C and N content. We expected oribatid mite density to increase with increasing tree diversity, but we expected the effects of tree species identity to override effects of tree diversity. Further, we hypothesized the density of oribatid mites to be reduced by the presence of beech but increased by the presence of lime and ash. As expected tree diversity little affected oribatid mite communities, whereas tree species identity strongly altered density and community structure of oribatid mites. However, in contrast to our expectations the density of oribatid mites was highest in presence of beech indicating that many oribatid mite species benefit from the presence of recalcitrant litter forming thick organic layers. Especially Oppioidea benefited from the presence of beech presumably due to an increased availability of food resources such as fungi and nematodes. Lower density of oribatid mites in monospecific clusters of lime and ash suggests that oribatid mites did not benefit from high quality litter of these species. Notably, large and strongly sclerotized oribatid mite species, such as Steganacarus magnus and Chamobates voigtsi, benefited from the presence of ash and lime. Presumably, these large species better resist harsh microclimatic conditions in shallow organic layers.     

内盖夫荒漠中小型土壤节肢动物群落的时空变化

Desert ecosystems are characterized by sparse vegetation that affects both abiotic parameters and soil biota along the soil profile.This study was conducted in 2010–2011 in a loess plain in the northern Negev Desert highlands, Israel, to test two main hypotheses:1) the abundance and diversity of microarthropods would vary seasonally in the top 30-cm soil layer, but would be relatively stable at soil depths between 30 and 50 cm and 2) soil microarthropods would be more abundant in soils under shrubs with large litter accumulations than under shrubs with less litter or bare soil. Soil samples were collected each season from the 0–50 cm profile at10-cm intervals under the canopies of Hammada scoparia and Zygophyllum dumosum and from the bare interspaces between them.Soil moisture and soil organic carbon in the top 30-cm layers varied seasonally, but there was little variation in the soil layers deeper than 30 cm. Soil mites were most abundant in the top 30-cm soil layer in autumn and winter, with the highest number of families found in winter. There were no differences in soil microarthropod abundance attributable to the presence or absence of shrubs of either species. The microarthropod communities of the microhabitats studied consisted of Acari, Psocoptera, and Collembola. The Acari were mostly identified to the family level and were dominated by Oribatida(55%) and Prostigmata(41%) in all seasons and microhabitats, while the psocopterans were most abundant in summer. These results are opposite to those obtained in other studies in similar xeric environments. Moreover, our findings were not in line with our hypothesis that a better microhabitat played a major role in microarthropod community composition, diversity, and density.     

Effects of forest stand type on oribatid mite (Acari: Oribatida) assemblages in a southwestern Quebec forest

Despite the ubiquity of oribatid mites in soil and litter systems, and their importance in decomposition and nutrient cycling processes, little is known of the factors underlying the composition of their assemblages. Our objective was to address this by determining how oribatid assemblage composition changes by forest stand type. This work was done in and near a hardwood forest in southwestern Quebec, Canada. We sampled mites by collecting 1 L of litter and 170 cm³ of soil from four sites in each of four distinct habitat types: American beech stands, sugar maple stands, mixed deciduous stands and mixed conifer plantations. Samples were collected in July and September 2005, and June 2006, and over 6500 oribatid mites were collected and identified to species. Abundance and species richness differed between forest types: for abundance conifer>beech>maple>mixed deciduous while for species richness beech and conifer>maple>mixed deciduous. Ordination analyses revealed that conifer plantations and beech stands supported distinct assemblages, while there were some overlap in the assemblages found in maple stands and mixed deciduous stands. These data support the importance of aboveground plant communities in affecting the composition of oribatid assemblages even at local scales and provide insight into additional impacts that may be caused by shifts in plant species ranges due to global changes.     

Community structure of oribatid mites in relation to elevation and geology on the slope of Mount Kinabalu,Sabah, Malaysia

The patterns of oribatid communities were investigated in relation to elevations (700, 1700, 2700 and 3100 m a.s.l.) and geological substrates (i.e. non-ultrabasic and ultrabasic rocks) on the slopes of Mt. Kinabalu, Sabah, Malaysia. The density and morphospecies richness of oribatid mites were greater in the non-ultrabasic plot than in the ultrabasic plot at each of the same elevations. The density and richness of Oribatid mites decreased with elevation on both substrates, but the effects of elevation on the density on non-ultrabasic were less significant than on the ultrabasic substrate. Oribatid mite density correlated positively with the concentration of soil organic phosphorus and negatively with that of exchangeable Ca in soil. The richness of morphospecies of oribatid mites positively correlated with phosphorus concentration in litter, above-ground biomass, tree diversity and litterfall amount, and negatively correlated with elevation and Ca in soil. Morphospecies from families Galumnidae, Otocepheidae, Haplozetidae and Scheloribatidae were dominant in each plot. Canonical correspondence analysis (CCA) showed the importance of elevation for the community structure of oribatid mite. In conclusion, total density or morphospecies richness of oribatid communities was influenced by both geology and elevation, and morphospecies composition was strongly influenced by elevation.     

Connectivity of litter islands remaining after a fire and unburnt forest determines the recovery of soil fauna

Forest wildfires can dramatically affect soil communities and reduce abundance and diversity of soil fauna. The recovery of soil animals after a fire depends both on immigration from the unburnt forest and on local survival in less-burnt spots, but the relative importance of these mechanisms is poorly known. Therefore, these factors were studied with regard to soil macrofauna and soil mites seven years after a wildfire occurring in a pine forest area with shallow soil in 2001 in central Sweden. Three replicate transects, each consisting of four plots were studied. The plots were located in (i) the unburnt forest close to the fire edge; (ii) slightly burnt patches directly attached to the unburnt forest; (iii) slightly burnt patches surrounded by bare rock but connected to the unburnt forest edge by a corridor with mostly unburnt litter and vegetation; and (iv) island patches not connected with a corridor to the unburnt forest edge. The hypothesis was that that soil animals would particularly disperse from the unburnt forest to moderately burnt plots inside a burnt area via the network of less-burnt corridors. Poor dispersers would be especially few in the island patches lacking connection to the “mainland”, whereas good dispersers would be independent of gaps in connectivity. As expected, the highest abundance of both macrofauna and oribatid mites was found in the unburnt forest. Resident soil macro- and mesofauna representatives had half the abundance in the edge and corridor plots as compared to the control, but their abundance was not lower in the island plots than in the corridor plots indicating on-site survival and recovery. Mobile mesostigmatid mites did not show any significant reduction of abundance in any of the plots. The abundance of soil-dwelling oribatid mites did not differ between islands and unburnt forest, but mobile aboveground oribatids had significantly lower abundance on the islands than in the unburnt forest. The opposite was observed for aboveground and belowground oribatid mite species richness. In conclusion, belowground animals showed mainly local survival and seemed to be independent of corridors presence, whereas most aboveground and mobile macro- and mesofauna seemed to be more responsive to isolation induced by forest fires. Soil and litter corridors connecting unburnt patches inside the burnt forests with the unburnt edges were important mainly for less mobile groups of soil macrofauna. This supports the idea that there is a relatively slow process of soil ecosystem recovery and that external colonization of the burnt areas dominates over the local survival and recovery from refuges.     

Rot holes create key microhabitats for epiphytic lichens and bryophytes on beech (Fagus sylvatica)

Identification of trees with key microhabitats as well as knowledge of their ecological formation is important for the conservation of epiphytic bryophytes and lichens on beech. Based on the hypothesis that certain types of stem damage are crucial for the occurrence of epiphytes of conservation concern, we surveyed 145 beech trees (57-280 years) for different types of stem damage and analysed their relationship to other tree characteristics, epiphyte species and wood-inhabiting fungi in a forest landscape on acid soils.Three main types of stem damage were identified; canker, rot hole and surface rot. The incidence of rot holes was highest on trees with a low growth rate during the last 50 years, but was unrelated to tree size or age per se. Bark pH was significantly higher below than above rot holes, whereas no such relationship was found for cankers. Wood mould from rot holes had a very high pH, explaining the higher bark pH below this type of damage. The number of epiphyte species of conservation concern was strongly positively related to rot holes and high bark pH. Cankers had a weaker, yet significant positive effect. The fungus Psathyrella cernua was associated with the rot holes and is suggested to be a key species involved in creating this microhabitat.We conclude that slow-growing trees with rot holes are important for the conservation of epiphytes and should be selected as retention trees in managed forests. The study also highlights a potential for habitat restoration by inducing artificial damage and inoculation of decay fungi in beech trees.     

Forest fragment size and microhabitat effects on palm seed predation

The establishment of plant species depends crucially on where the seeds are deposited. However, since most studies have been conducted in continuous forests, not much is known about the effects of forest fragmentation on the maintenance of abiotic and biotic characteristics in microhabitats and their effects on seed survival. In this study, we evaluated the effects of forest fragmentation on the predation upon the seeds of the palm Syagrus romanzoffiana in three microhabitats (interior forest, forest edge and gaps) in eight fragments of semi-deciduous Atlantic forest ranging in size from 9.5 ha to 33,845 ha in southeastern Brazil. Specifically, we examined the influence of the microhabitat structure, fauna and fragment size on the pattern of seed predation. Fragments <100 ha showed similar abiotic and biotic characteristics to those of the forest edge, with no seed predation in these areas. Forest fragments 230-380 ha in size did not present “safe sites” for S. romanzoffiana seed survival and showed high seed predation intensity in all microhabitats evaluated. In fragments larger than 1000 ha, the seed predation was lower, with abiotic and biotic differences among gaps, interior forests and forest edges. In these fragments, the survival of S. romanzoffiana seeds was related to squirrel abundance and interior forest maintenance. Based on these results, we concluded that there are no safe sites for S. romanzoffiana seed establishment in medium- and small-sized fragments as result of the biotic and abiotic pressure, respectively. We suggest that on these forest fragments, management plans are needed for the establishment of S. romanzoffiana, such as interior forest improvement and development in small-sized sites in order to minimize the edge effects, and on medium-sized fragments, we suggest post-dispersal seed protection in order to avoid seed predation by vertebrates. Our findings also stress the importance of assessing the influence of forest fragmentation on angiosperm reproductive biology as part of the effective planning for the management of fragmented areas.     

Molecular detection of nematode predation and scavenging in oribatid mites: Laboratory and field experiments

Recent stable isotope analyses indicate that a number of putative detritivorous soil microarthropods is not typical detritivores but rather live as predators or scavengers. Using molecular gut content analyses the present study investigates if nematodes indeed form part of the diet of oribatid mites. First, in a no-choice laboratory feeding experiment two nematode species (Phasmarhabditis hermaphrodita and Steinernema feltiae) were offered to eight species of oribatid mites and one gamasid mite. Second, after feeding for 4 and 48 h on each nematode species the detection time of prey DNA in the oribatid mite species Steganacarus magnus was investigated. Third, in a field experiment nematode prey (P. hermaphrodita and S. feltiae) in the diet of microarthropods was investigated distinguishing between scavenging and predation. In the no-choice laboratory experiment not only the gamasid mite but also several of the studied oribatid mite species consumed nematodes. After feeding on nematodes for 4 h prey DNA was detectable in S. magnus for only 4 h, but after feeding for 48 h prey DNA was detectable for 128 h, indicating that the duration of feeding on prey is an important determinant for prey DNA detection. The field experiment confirmed that oribatid mite species including Liacarus subterraneus, Platynothrus peltifer and S. magnus intensively prey on nematodes. Interestingly, DNA of dead P. hermaphrodita was detectable to a similar degree as that of living individuals indicating that scavenging is of significant importance in decomposer food webs. Results of our study indicate that predation and scavenging on nematodes by “detritivorous” microarthropods in soil food webs need to be reconsidered.     

Trophic stability of soil oribatid mites in the face of environmental change

A key issue in ecology is the degree to which trophic structure within communities responds to environmental change. Organisms with generalist diets are more flexible in their feeding habits than are specialists, and may be affected less in a changing environment. Soil fauna fulfill crucial ecosystem functions in terrestrial ecosystems and many are thought to have generalized diets. They may therefore be buffered from negative effects of environmental change. Here, we used ¹⁵N isotope analysis to study trophic differentiation among 91 species of oribatid mites and their responses to chronic atmospheric N deposition. Combining our own measurements with published data, we established that the trophic positions of mite species were remarkably stable within and among forests, as well as between ambient and experimental N deposition. Trophic stability indicates a higher than expected level of feeding specialization, which may foster diversity, but limit the ability to switch food resources in a changing environment.