RESUMO
Heathland restoration using topsoil removal requires the re-colonization of above- and belowground communities. Oribatid mites play a key role in the comminution of organic matter and are frequently early colonizers during succession despite their limited mobility. Whereas the assembly of their communities may take decades, passive dispersal likely dominates colonization processes, but especially dispersal via other animals (phoresy) remains poorly studied. Compared to other potential hosts, movement habits and ecology of small rodents may provide dispersal advantages to oribatid communities. We studied dispersal of oribatid mites via small rodents in restored heathland sites of different age. We measured movement patterns of small rodents and extracted mites from their pelts and nests to estimate annual contributions of these rodents to the dispersal of oribatids. We also discussed phoretic estimates reported on other host groups as a reference. Probability estimates of oribatids in pelts and nests showed lower occurrence frequencies compared to other reported phoretic hosts. However, local rodent communities may aid the dispersal of up to 41,000 oribatid mites per year. We highlight the high diversity of oribatid species mounting rodents, unlike strong species-specific filters reported in other passive pathways. We found that over half (58%) of the oribatid species reproduced asexually and over a third (32%) had a soil-dwelling lifestyle. We also observed that rodents often travel short distances below 40 m, but occasionally reach distances of up to 100 m, especially in earlier successional stages. Synthesis and applications. Our results suggest that rodents may contribute to assembly processes of soil-dwelling oribatid communities given the slow turnover rate of this group in heathlands. This is accomplished through short-distance dispersal, and especially in sites at early stages of succession. To our knowledge, we are the first to quantitatively assess the potential dispersal of oribatid mites via rodents.
RESUMO
The Sea Scheldt estuary has been suggested to be a significant pathway for transfer of plastic debris to the North Sea. We have studied 12,801 plastic items that were collected in the Sea Scheldt estuary (Belgium) during 3 sampling campaigns (in spring, summer, and autumn) using a technique called anchor netting. The investigation results indicated that the abundance of plastic debris in the Scheldt River was on average 1.6 × 10-3 items per m3 with an average weight of 0.38 × 10-3 g per m3. Foils were the most abundant form, accounting for >88 % of the samples, followed by fragments for 11 % of the samples and filaments, making up for <1 % of the plastic debris. FTIR spectroscopy of 7 % of the total number of plastic debris items collected in the Sea Scheldt estuary (n = 883) revealed that polypropylene (PP), polyethylene (PE), and polystyrene (PS) originating from disposable packaging materials were the most abundant types of polymers. A limited number of plastic debris items (n = 100) were selected for non-destructive screening of their mineral element composition using micro-X-ray fluorescence spectrometry (µXRF). The corresponding results revealed that S, Ca, Si, P, Al, and Fe were the predominant mineral elements. These elements originate from flame retardants, mineral fillers, and commonly used catalysts for plastic production. Finally, machine learning algorithms were deployed to test a new concept for forensic identification of the different plastic entities based on the most important elements present using a limited subset of PP (n = 36) and PE (n = 35) plastic entities.