Niches, rather than neutrality, structure a grassland pioneer guild

Pioneer species are fast-growing, short-lived gap exploiters. They are prime candidates for neutral dynamics because they contain ecologically similar species whose low adult density is likely to cause widespread recruitment limitation, which slows competitive dynamics. However, many pioneer guilds appear to be differentiated according to seed size. In this paper, we compare predictions from a neutral model of community structure with three niche-based models in which trade-offs involving seed size form the basis of niche differentiation. We test these predictions using sowing experiments with a guild of seven pioneer species from chalk grassland. We find strong evidence for niche structure based on seed size: specifically large-seeded species produce fewer seeds but have a greater chance of establishing on a per-seed basis. Their advantage in establishment arises because there are more microsites suitable for their germination and early establishment and not directly through competition with other seedlings. In fact, seedling densities of all species were equally suppressed by the addition of competitors' seeds. By the adult stage, despite using very high sowing densities, there were no detectable effects of interspecific competition on any species. The lack of interspecific effects indicates that niche differentiation, rather than neutrality, prevails

Acrylamide: Increased concentrations in homemade food and first evidence of its variable absorption from food, variable metabolism and placental and breast milk transfer in humans

We have developed a liquid chromatography/mass spectrometry (LC-MS/MS) assay to determine acrylamide in various body fluids. The assay also allows the reliable quantitation of acrylamide in food. In a total of 11 healthy male and female subjects, we were able to show that acrylamide from food given to humans is in fact absorbed from the gut. The half-lives determined in two male subjects were 2.2 and 7 h. Acrylamide was found in human breast milk and penetrated the human placenta (n = 3). The variability of acrylamide concentrations found in this investigation is most likely caused by variable intersubject bioavailability and metabolism. This may be an important indication that the assessment of the risk from acrylamide for the individual may be very difficult without knowing the concentrations of acrylamide in the body. This should be considered in the design of any risk assessment study or post hoc analysis of earlier studies. At this time, we suggest that pregnant women and breast-feeding mothers avoid acrylamide-containing food. Copyright (C) 2002 S. Karger AG, Basel

Real-time multi-image vignetting and exposure correction for image stitching

Seamless image stitching depends not only on the accurate alignments of camera images, but also on the compensation of illumination inconsistencies. Even if two images are aligned perfectly, the seam is still visible if the images have a distinct vignetting or different exposure. Image stitching is used to expand the field of view, but a visible seam can lead to significant errors in subsequent visual perception tasks. As a result, we present a straightforward and accurate method for vignetting and exposure correction for stitched images. Firstly, we estimate the camera response function that maps irradiance to intensity. Then, the vignetting model is determined, which is applied to the irradiance images. After that, the exposure of the stitched images is corrected with the irradiance values at the seam. Finally, the irradiance is converted back into intensity using the camera response function. Our approach is evaluated using data recorded by our experimental vehicle and the public nuScenes dataset. Thereby, we test the performance of our method using the IoU of the histograms as well as the mean absolute error of the intensity values in the overlapping image regions. Further more, we demonstrate the real-time capability of our approach