Pitfall trap sampling bias depends on body mass, temperature, and trap number: insights from an individual-based model

The diversity and community composition of ground arthropods is routinely analyzed by pitfall trap sampling, which is a cost- and time-effective method to gather large numbers of replicates but also known to generate data that are biased by species-specific differences in locomotory activity. Previous studies have looked at factors that influence the sampling bias. These studies, however, were limited to one or few species and did rarely quantify how the species-specific sampling bias shapes community-level diversity metrics. In this study, we systematically quantify the species-specific and community-level sampling bias with an allometric individual-based model that simulates movement and pitfall sampling of 10 generic ground arthropod species differing in body mass. We perform multiple simulation experiments covering different scenarios of pitfall trap number, spatial trap arrangement, temperature, and population density. We show that the sampling bias decreased strongly with increasing body mass, temperature, and pitfall trap number, while population density had no effect and trap arrangement only had little effect. The average movement speed of a species in the field integrates body mass and temperature effects and could be used to derive reliable estimates of absolute species abundance. We demonstrate how unbiased relative species abundance can be derived using correction factors that need only information on species body mass. We find that community-level diversity metrics are sensitive to the particular community structure, namely the relation between body mass and relative abundance across species. Generally, pitfall trap sampling flattens the rank-abundance distribution and leads to overestimations of ground arthropod Shannon diversity. We conclude that the correction of the species-specific pitfall trap sampling bias is necessary for the reliability of conclusions drawn from ground arthropod field studies. We propose bias correction is a manageable task using either body mass to derive unbiased relative abundance or the average speed to derive reliable estimates of absolute abundance from pitfall trap sampling

Spatial organization and population size of small Cucuteni-Tripolye settlements: Results of geomagnetic surveys in Baia and Adâncata, Suceava County, Bucovina, Eastern Romania

Geomagnetic research and drillings provide new results regarding settlement organisation and population size of three small settlements from the Pre-Cucuteni and Cucuteni AB period in the Suceva County in Romanian Bucovina. In these settlements from different stages of the Pre-Cucuteni complex domestic dwellings can be distinguished from clearly oversized (special?) buildings which are situated in central positions and which contain partly special inventories. Different principles of settlement organisation are visible which show each far-reaching references to the Central Balkans on the one hand and the Bug-Dnieper interfluve on the other hand. Consistently populations with less than 200 inhabitants are reconstructed based on analogies to other Cucuteni-Tripolye sites

Sand mining in the Mekong Delta revisited - current scales of local sediment deficits

The delta of the Mekong River in Vietnam has been heavily impacted by anthropogenic stresses in recent years, such as upstream dam construction and sand mining within the main and distributary channels, leading to riverbank and coastal erosion. Intensive bathymetric surveys, conducted within the Tien River branch during the dry and wet season 2018, reveal a high magnitude of sand mining activities. For the year 2018, an analysis of bathymetric maps and the local refilling processes leads to an estimated sand extraction volume of 4.64 ± 0.31 Mm3/yr in the study area, which covered around 20 km. Reported statistics of sand mining for all of the Mekong’s channels within the delta, which have a cumulative length of several hundred kilometres, are 17.77 Mm3/yr for this period. Results from this study highlight that these statistics are likely too conservative. It is also shown that natural sediment supplies from upper reaches of the Mekong are insufficient to compensate for the loss of extracted bed aggregates, illustrating the non-sustainable nature of the local sand mining practices

Spatial organisation and population size of small Cucuteni-Tripolye settlements: Results of geomagnetic surveys in Baia and Adâncata, Suceava County, Bucovina, Eastern Romania

Geomagnetic research and drillings provide new results regarding settlement organisation and population size of three small settlements from the Pre-Cucuteni and the Cucuteni A-B period of Suceava County in Romanian Bucovina. In these settlements from different stages of the Cucuteni-Tripolye complex, domestic dwellings can be distinguished from clearly oversized (special?) buildings, which are situated in central locations and sometimes contain special inventories. Different principles of settlement organisation are visible, which each show far-reaching references to the Central Balkans, on the one hand, and the Bug-Dnieper interfluve on the other hand. Based on analogies with other Cucuteni-Tripolye sites, consistent populations with less than 200 inhabitants are reconstructed

Pitfall trap sampling bias depends on body mass, temperature, and trap number: insights from an individual-based model

The diversity and community composition of ground arthropods is routinely analyzed by pitfall trap sampling, which is a cost- and time-effective method to gather large numbers of replicates but also known to generate data that are biased by species-specific differences in locomotory activity. Previous studies have looked at factors that influence the sampling bias. These studies, however, were limited to one or few species and did rarely quantify how the species-specific sampling bias shapes community-level diversity metrics. In this study, we systematically quantify the species-specific and community-level sampling bias with an allometric individual-based model that simulates movement and pitfall sampling of 10 generic ground arthropod species differing in body mass. We perform multiple simulation experiments covering different scenarios of pitfall trap number, spatial trap arrangement, temperature, and population density. We show that the sampling bias decreased strongly with increasing body mass, temperature, and pitfall trap number, while population density had no effect and trap arrangement only had little effect. The average movement speed of a species in the field integrates body mass and temperature effects and could be used to derive reliable estimates of absolute species abundance. We demonstrate how unbiased relative species abundance can be derived using correction factors that need only information on species body mass. We find that community-level diversity metrics are sensitive to the particular community structure, namely the relation between body mass and relative abundance across species. Generally, pitfall trap sampling flattens the rank-abundance distribution and leads to overestimations of ground arthropod Shannon diversity. We conclude that the correction of the species-specific pitfall trap sampling bias is necessary for the reliability of conclusions drawn from ground arthropod field studies. We propose bias correction is a manageable task using either body mass to derive unbiased relative abundance or the average speed to derive reliable estimates of absolute abundance from pitfall trap sampling

Digital elevation models showing sand mining activities within the Tien River branch, Vietnamese Mekong Delta

Bathymetric surveys were conducted within the Vietnamese Mekong Delta in April/May 2018 and September/October 2018 during the dry and wet season, respectively. The study area was focused on a 20 km stretch of the Tien River branch, located between the city of Sa Dec and the bifurcation spot of the Tien River with the Co Chien River near Vinh Long. Processed bathymetric data was interpolated onto a grid with a resolution of 1 x 1 m, while the Earth Gravitational Model 2008 was used as vertical reference system. The bathymetric maps were used to estimate annual sand mining activity and bed load transport rates within the study area. For more details on the processing of the data, see the corresponding paper and supplementary information

CD28-dependent Rac1 activation is the molecular target of azathioprine in primary human CD4(+) T lymphocytes

Azathioprine and its metabolite 6-mercaptopurine (6-MP) are immunosuppressive drugs that are used in organ transplantation and autoimmune and chronic inflammatory diseases such as Crohn disease. However, their molecular mechanism of action is unknown. In the present study, we have identified a unique and unexpected role for azathioprine and its metabolites in the control of T cell apoptosis by modulation of Rac1 activation upon CD28 costimulation. We found that azathioprine and its metabolites induced apoptosis of T cells from patients with Crohn disease and control patients. Apoptosis induction required costimulation with CD28 and was mediated by specific blockade of Rac1 activation through binding of azathioprine-generated 6-thioguanine triphosphate (6-Thio-GTP) to Rac1 instead of GTP. The activation of Rac1 target genes such as mitogen-activated protein kinase kinase (MEK), NF-κB, and bcl-x(L) was suppressed by azathioprine, leading to a mitochondrial pathway of apoptosis. Azathioprine thus converts a costimulatory signal into an apoptotic signal by modulating Rac1 activity. These findings explain the immunosuppressive effects of azathioprine and suggest that 6-Thio-GTP derivates may be useful as potent immunosuppressive agents in autoimmune diseases and organ transplantation